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I'm putting a C4 front suspension into my trans am!!

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Old 09-15-2017, 06:02 PM   #1
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I'm putting a C4 front suspension into my trans am!!

Yes, you read that right...I finally broke down and couldn't take the factory suspension/steering setup anymore, so I bought an entire front suspension out of a 1990 C4 corvette. It will be making it's way into my trans am and will be fully documented on video from start to finish. This will cure many of the 3rd gen front suspension woes, such as crappy geometry on a lowered/modified car, wandering with wider tires due to the gearbox slop, and as an added bonus, dropping nearly 70 lbs off the nose.

Here's the first few videos in the series so you can see where I'm at right now. I'll be trying to get a new video posted every week or so, so if you like what you see, be sure to subscribe to my youtube channel so you get the updates as I post them! I'll also be doing a J&M caster/camber plate giveaway if I hit 3000 subscribers, so keep your eyes open for a chance to win some free stuff


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Old 09-15-2017, 08:44 PM   #2
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Re: I'm putting a C4 front suspension into my trans am!!

sub'd

Back during the early years of car craft's Real Street Eliminator, a blue thirdgen transam with c4 rear suspension won. Can't remember if it had the c4 front though.
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Old 09-15-2017, 09:57 PM   #3
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Re: I'm putting a C4 front suspension into my trans am!!

Might want to wait until you see what Speedtech comes up with. They are doing a front clip with Ron Sutton for our cars.
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Old 09-15-2017, 11:52 PM   #4
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Re: I'm putting a C4 front suspension into my trans am!!

Wow thats gonna be one hell of a third gen! Gorgeous t/a
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Old 09-16-2017, 02:11 AM   #5
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Re: I'm putting a C4 front suspension into my trans am!!

Quote:
Originally Posted by rgauder View Post
sub'd

Back during the early years of car craft's Real Street Eliminator, a blue thirdgen transam with c4 rear suspension won. Can't remember if it had the c4 front though.
Thanks for the sub! I don't recall seeing that article, but theres no doubt the vette suspension both front and rear has much more engineering into it than the stock 3rd gen setup. I have heard of a few people doing the IRS vette rear, but theres only one other 3rd gen I know of that has done the C4 front, and I have spoken to him a bit about it. The swap is very popular in older cars and I have read dozens of posts where the owner had nothing but praise to say about what the vette setup transformed their car into.

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Originally Posted by QwkTrip View Post
Might want to wait until you see what Speedtech comes up with. They are doing a front clip with Ron Sutton for our cars.
I'm sure it will be a killer setup, but the difference is that I paid $400 for the complete C4 front suspension and should be able to fab it in all said and done for no more than another $500 or so once I fully rebuild it and buy some metal stock. I'm sure the speedtech setup will be very similar to the C4 suspension since it seems to be the industry standard for swapping into older cars, and I'm betting it will have quite the price tag on it as well!

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Wow thats gonna be one hell of a third gen! Gorgeous t/a
Thank you!
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Old 09-16-2017, 06:30 PM   #6
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Re: I'm putting a C4 front suspension into my trans am!!

I'll believe this when I see it.

Don't know a damn thing about Speedtech, but I DO know what a C4 looks like. I also know what "most older cars" look like, which is NOTHING CLOSE TO what our cars are like.

Trust me, I'll be watching your progress. Could be cool, could be ... something else.
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Old 09-16-2017, 09:42 PM   #7
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Re: I'm putting a C4 front suspension into my trans am!!

Looked into this years back and oddly enough the two cars have the same width "frame" in the front, so its probably not as hard to fit a c4 front setup than you might think.
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Old 09-17-2017, 03:21 AM   #8
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Re: I'm putting a C4 front suspension into my trans am!!

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Originally Posted by sofakingdom View Post
I'll believe this when I see it.

Don't know a damn thing about Speedtech, but I DO know what a C4 looks like. I also know what "most older cars" look like, which is NOTHING CLOSE TO what our cars are like.

Trust me, I'll be watching your progress. Could be cool, could be ... something else.
The biggest thing that turns people off is the fact that our cars are unibody and do not have a true front sub frame. But realistically, theres no difference other than one can be removed, and the other is a permanent part of the car. The C4 K-member is unique in that the entire suspension literally bolts to it...so make the K-member fit the car, and you have a vette front suspension. Obviously there are lots of precise measurements and some modifying of the frame rails and vette K-member, but I have it rigged up under my ar at the moment and it truly is a bit scary at how close the fit is. I'll make it work, I promise. This project will be one that gets finished

Quote:
Originally Posted by //<86TA>\\ View Post
Looked into this years back and oddly enough the two cars have the same width "frame" in the front, so its probably not as hard to fit a c4 front setup than you might think.
You are correct. The 3rd gen frame is slightly wider so you have to add about 3/4" of filler metal on the inside of each of the 3rd gens frame rails, but it is a very close fit all things considered. After taking some preliminary measurements, all it looks like I need to do is cut off the vette motor mounts and fab my own, clearance the K-member slightly for the LS oil pan, and drop the rack about an inch which there is room to do. Other than that, basically all just measuring and squaring it all up. I'm very excited for this project to really start taking shape after seeing how good of a fit it actually is!
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Old 09-17-2017, 03:56 AM   #9
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Re: I'm putting a C4 front suspension into my trans am!!

If you drop the track an inch be mindful of posable bump steer issues....
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Old 09-17-2017, 04:20 AM   #10
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Re: I'm putting a C4 front suspension into my trans am!!

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Originally Posted by daferris View Post
If you drop the track an inch be mindful of posable bump steer issues....
Nothing a simple 1" bumpstop kit wouldn't fix. The steering geometry will remain identical if both the rack and where the outer tie rods mount to the knuckle are both dropped 1".
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Old 09-17-2017, 11:08 AM   #11
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Re: I'm putting a C4 front suspension into my trans am!!

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Old 09-17-2017, 05:44 PM   #12
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Re: I'm putting a C4 front suspension into my trans am!!

If I can stop you and discourage you- I'll explain why. Hopefully it is not too late to just bolt things back together.

Corvette ackerman is no better then the 3rd gen ackerman. They are both close to zero which means the inside tire does not increase enough over the outside tire in turning angle.

You have other issues as well....
Note the track width of a 90 vette is 59.6" which is the centerline of front tire tread on a 9.5" wide wheel.

Now compare that to the factory 3rd gen track with of 61.4 considering the 16mm offset on the 8" wheel. You already have a positive scrub radius of about 1" from the ground pivot point of the factory 3rd gen geometry. You now go to the Vette suspension and a 3rd gen body offset offset wheel at aprox 72" overall width instead of a 71" with a factory 9.5 wheel...now you will have a positive scrub radius of about 2 3/4" which will really make the car a handful under hard braking as it wants to yank the steering wheel out of your grip.

I admire you ability to fabricate and to take on such a task, just know you are doing this with really no positive outcome and it is a hell of a lot of work. Scrub radius is the biggest concern since it is over 20% the wheel width is a general no-no. The steering rack will be a big asset for driver control to overcome this in driver comfort but understand regardless of driver comfort it will be hard to keep the car positioned on the track where you want it for corner entry.

Edit to add: as a further note, GM still has their heads up their asses with in reference to Corvette ackerman even in the c5,c6 and the new C7 are still all terrible

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Old 09-17-2017, 05:46 PM   #13
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Re: I'm putting a C4 front suspension into my trans am!!

The SpeedTech was announced last year, but I don't know that they have actually done one, yet.
The promo:
https://www.youtube.com/watch?v=h2S3...ature=youtu.be

And some Ron reply text to 3rd Gen question:
Hey James,

The geometry on this clip is in line with my TA2 race clip, except the Speedtech clip puts the roll center in the optimum spot regardless of how much you travel the front end. This is the first time I've achieved this ... so this clip would work awesome for any setup a person chooses. So if someone runs a stiff spring set-up & only travels the front end around an inch ... the roll center is at 2" above ground, which is optimum for that setup. If they high travel the front end ... say 3" ... with soft springs & a larger sway bar ... the roll center is at ground level ... again, optimum for that setup. in moderate travel ... around 2" ... the RC is at 1" - perfect.

The dual power Sweet rack will handle the load from the high grip suspension & 315 front tires (TW200 or slicks) with ease. No rebuilt $300 OEM racks here. This puppy cost almost $1000, but it is built to take the loads we're creating these days.

I forget if you have my AutoX-Star or Track-Star valved Ridetech shocks on the OLC Camaro. But these clips are available with my Track-Star "secret sauce" digressive valved shocks in single or triple adjustable.

* Quick side note: On Friday May 27th, I went shock testing with a championship GT team that races in the Western Endurance GT car series at Buttonwillow (because it's a bumpy track - perfect for shock testing). They ran a best of 1:49.9 with their Bilstein race shocks. Then ran a best of 1:46.8 ... 3.1 seconds quicker ... my Track-Star valved Ridetech triples. The driver couldn't believe the grip increase. These are the same shocks I make available to the Pro-Touring world, and are optional on this Speedtech clip.

All the geometry on this Speedtech ExtReme front clip is spot on:
* Roll Center location & dynamic migration - Optimum grip
* Bump steer changes only .001" in 3" travel
* Anti-dive is 40% - allowing us to run softer springs & still achieve a low roll angle
* Ackerman is 100% - Creating optimum slip angle on inside front tire
* Dynamic Camber/Caster creates optimum contact patches on BOTH front tires
* Jacking effect is Nil - allowing softer springs & still achieve a low roll angle
* Front Sway bar rate range is from 400# to over 3000#

This would be extremely racy for your new 3rd gen.

I guess if you have the $$ to do this, you might as well opt for the triple adjustable JRI's!!!!
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Old 09-17-2017, 06:12 PM   #14
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Re: I'm putting a C4 front suspension into my trans am!!

Quote:
Originally Posted by TEDSgrad View Post
The SpeedTech was announced last year, but I don't know that they have actually done one, yet.
The promo:
https://www.youtube.com/watch?v=h2S3...ature=youtu.be

And some Ron reply text to 3rd Gen question:
Hey James,

The geometry on this clip is in line with my TA2 race clip, except the Speedtech clip puts the roll center in the optimum spot regardless of how much you travel the front end. This is the first time I've achieved this ... so this clip would work awesome for any setup a person chooses. So if someone runs a stiff spring set-up & only travels the front end around an inch ... the roll center is at 2" above ground, which is optimum for that setup. If they high travel the front end ... say 3" ... with soft springs & a larger sway bar ... the roll center is at ground level ... again, optimum for that setup. in moderate travel ... around 2" ... the RC is at 1" - perfect.

The dual power Sweet rack will handle the load from the high grip suspension & 315 front tires (TW200 or slicks) with ease. No rebuilt $300 OEM racks here. This puppy cost almost $1000, but it is built to take the loads we're creating these days.

I forget if you have my AutoX-Star or Track-Star valved Ridetech shocks on the OLC Camaro. But these clips are available with my Track-Star "secret sauce" digressive valved shocks in single or triple adjustable.

* Quick side note: On Friday May 27th, I went shock testing with a championship GT team that races in the Western Endurance GT car series at Buttonwillow (because it's a bumpy track - perfect for shock testing). They ran a best of 1:49.9 with their Bilstein race shocks. Then ran a best of 1:46.8 ... 3.1 seconds quicker ... my Track-Star valved Ridetech triples. The driver couldn't believe the grip increase. These are the same shocks I make available to the Pro-Touring world, and are optional on this Speedtech clip.

All the geometry on this Speedtech ExtReme front clip is spot on:
* Roll Center location & dynamic migration - Optimum grip
* Bump steer changes only .001" in 3" travel
* Anti-dive is 40% - allowing us to run softer springs & still achieve a low roll angle
* Ackerman is 100% - Creating optimum slip angle on inside front tire
* Dynamic Camber/Caster creates optimum contact patches on BOTH front tires
* Jacking effect is Nil - allowing softer springs & still achieve a low roll angle
* Front Sway bar rate range is from 400# to over 3000#

This would be extremely racy for your new 3rd gen.

I guess if you have the $$ to do this, you might as well opt for the triple adjustable JRI's!!!!
These guys never tell the whole story. It has to be made chassis specific and has to be designed for a specific tires height AND a specific chassis height. HEck, to be sarcastic, my Mercedes bumps perfectly through 4.5 " travel until I got it into a lowered static range and then it went to ****....lol. This guy is just selling expensive parts to people that hear what they want to hear.

Once you buy his stuff and it is not working as he claims, he will tell you the ride height is too low, your caster is too much, your front RC is perfect for a 3000 lb car with a rear RC at such and such height but yours is different, etc etc etc. Snake oil sales.

Last edited by SlickTrackGod; 09-17-2017 at 06:15 PM.
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Old 09-18-2017, 02:35 AM   #15
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Re: I'm putting a C4 front suspension into my trans am!!

Quote:
Originally Posted by SlickTrackGod View Post
If I can stop you and discourage you- I'll explain why. Hopefully it is not too late to just bolt things back together.

Corvette ackerman is no better then the 3rd gen ackerman. They are both close to zero which means the inside tire does not increase enough over the outside tire in turning angle.

You have other issues as well....
Note the track width of a 90 vette is 59.6" which is the centerline of front tire tread on a 9.5" wide wheel.

Now compare that to the factory 3rd gen track with of 61.4 considering the 16mm offset on the 8" wheel. You already have a positive scrub radius of about 1" from the ground pivot point of the factory 3rd gen geometry. You now go to the Vette suspension and a 3rd gen body offset offset wheel at aprox 72" overall width instead of a 71" with a factory 9.5 wheel...now you will have a positive scrub radius of about 2 3/4" which will really make the car a handful under hard braking as it wants to yank the steering wheel out of your grip.

I admire you ability to fabricate and to take on such a task, just know you are doing this with really no positive outcome and it is a hell of a lot of work. Scrub radius is the biggest concern since it is over 20% the wheel width is a general no-no. The steering rack will be a big asset for driver control to overcome this in driver comfort but understand regardless of driver comfort it will be hard to keep the car positioned on the track where you want it for corner entry.

Edit to add: as a further note, GM still has their heads up their asses with in reference to Corvette ackerman even in the c5,c6 and the new C7 are still all terrible
The track width for a 90 vette is actually 61.5 inches...almost identical to a third gen. The earlier suspensions were the ones that were 1.5" or so narrower.

As for the scrub radius, this car is being built purely for street use. Even if it were not the greatest, it will never go on a track, autocross course, etc. Occasionally it will hit a drag strip but it will be a 99% street car. I'm doing this retrofit for the sole reason of getting a more enjoyable driving experience out of the car and having an overall tighter steering feel and a factory designed suspension that I won't have to make any modifications to.

Also, because I will be installing this suspension so that everything is positioned how it's supposed to be at the ride height I want, there will be no off angles on control arms or any other part of it, so the car will sit lower than "stock," yet still retain perfect factory geometry of the vette setup. Theres only one other 3rd gen I've seen that had this swap performed, and it's not running yet. So really, everything will be speculation until I get a legitimate driving example to go off of.

The vette setup has 7-8* of caster built into it which coupled with rack steering should give a nice tight steering feel with wide tires. Once I couple a set of coilovers with it after it's installed, it should ride even better than a factory vette.

Quote:
Originally Posted by TEDSgrad View Post
The SpeedTech was announced last year, but I don't know that they have actually done one, yet.
The promo:
https://www.youtube.com/watch?v=h2S3...ature=youtu.be
To be honest, that looks like an overly fancy and colorful (did I mention much heavier!) redesign of the corvette setup. I can tell you for a fact that the upper ball joint is in fact a C4 vette piece. I think most of these aftermarket companies try to reinvent the wheel when it comes to suspensions, and then they sell it for crazy big bucks. A corvette was designed with an unlimited budget through a major auto manufacturer and in my opinion, you just aren't going to get that sort of R&D in a small suspension company.
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Old 09-18-2017, 11:13 AM   #16
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Re: I'm putting a C4 front suspension into my trans am!!

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Originally Posted by whitedevilTA View Post
The track width for a 90 vette is actually 61.5 inches...almost identical to a third gen. The earlier suspensions were the ones that were 1.5" or so narrower.

As for the scrub radius, this car is being built purely for street use. Even if it were not the greatest, it will never go on a track, autocross course, etc. Occasionally it will hit a drag strip but it will be a 99% street car. I'm doing this retrofit for the sole reason of getting a more enjoyable driving experience out of the car and having an overall tighter steering feel and a factory designed suspension that I won't have to make any modifications to.

Also, because I will be installing this suspension so that everything is positioned how it's supposed to be at the ride height I want, there will be no off angles on control arms or any other part of it, so the car will sit lower than "stock," yet still retain perfect factory geometry of the vette setup. Theres only one other 3rd gen I've seen that had this swap performed, and it's not running yet. So really, everything will be speculation until I get a legitimate driving example to go off of
Here is why you are wrong. You are measuring hub face to hub face to eyour track width comparison from the Vette to the third gen. It is not done that way due to scrub radius (something apparently you obviously do not understand from your comment). THE VETTE PLATFORM RELIES ON HIGH NEGATIVE OFFSET WHEELS. Good luck with this. As for not knowing until it's tried? Wow. You may have fabricating skills, but lack chassis dynamics knowledge.

Why even do this if it is "just a street car? You will go around for the rest of your life boasting...Hey its got a corvette front end"

so?
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Old 09-18-2017, 11:32 AM   #17
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Re: I'm putting a C4 front suspension into my trans am!!

I'm not as skeptical as Dean is. I do think Ron and SpeedTech can do an amazing job.

What I do question is the worth!
I've been able to modify my suspension to the point where the weak link is the driver. What is the purpose and worth of creating something so far beyond my own capabilities? And what would be the benefit-to-cost ratio if someone actually went this far? I still want to see someone do it, though - just not my feeble wallet.

Kyle Tucker is an amazing driver; competes and wins out on the Optimum circuit. For someone like him, it might make sense. I'm waiting to see and hear more results from their Camaro 2.0 build. I want to hear more insight from a quality driver who has taken the McStrut to it's limit; then, I could evaluate the project of eliminating the strut, altogether, from a quality driver who knows both set-ups well.
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Old 09-18-2017, 11:44 AM   #18
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Re: I'm putting a C4 front suspension into my trans am!!

Quote:
Originally Posted by SlickTrackGod View Post
Here is why you are wrong. You are measuring hub face to hub face to eyour track width comparison from the Vette to the third gen. It is not done that way due to scrub radius (something apparently you obviously do not understand from your comment). THE VETTE PLATFORM RELIES ON HIGH NEGATIVE OFFSET WHEELS. Good luck with this. As for not knowing until it's tried? Wow. You may have fabricating skills, but lack chassis dynamics knowledge.

Why even do this if it is "just a street car? You will go around for the rest of your life boasting...Hey its got a corvette front end"

so?
I appreciate the concern, but I have seen you tear into so many people on the forum for wanting to try new things. You seem extremely set in your ways, and thats fine. However, because of people like you, nothing new ever comes out of the third gen community because others constantly get beaten down and discouraged. I'm putting the C4 suspension in my car, period. I can almost 100% guarantee it will feel leagues better than the third gen setup. I may not be a suspension pro, but then again, I could care less to ever throw this car around a track. If it takes an alignment and drives down the street nicely, thats fine with me...that's all I need the car to do. And as for why I'm doing it? Because it's my car and I can do as I please with it. I have not found one single person that did the C4 front suspension on any type of car and had something negative to say about it. I go off of listening to people who have actually "been there, done that." Not just on speculation from people who simply think it's a dumb idea.
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Old 09-18-2017, 12:32 PM   #19
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Re: I'm putting a C4 front suspension into my trans am!!

Quote:
Originally Posted by whitedevilTA View Post
I appreciate the concern, but I have seen you tear into so many people on the forum for wanting to try new things. You seem extremely set in your ways, and thats fine. However, because of people like you, nothing new ever comes out of the third gen community because others constantly get beaten down and discouraged. I'm putting the C4 suspension in my car, period. I can almost 100% guarantee it will feel leagues better than the third gen setup. I may not be a suspension pro, but then again, I could care less to ever throw this car around a track. If it takes an alignment and drives down the street nicely, thats fine with me...that's all I need the car to do. And as for why I'm doing it? Because it's my car and I can do as I please with it. I have not found one single person that did the C4 front suspension on any type of car and had something negative to say about it. I go off of listening to people who have actually "been there, done that." Not just on speculation from people who simply think it's a dumb idea.
You're talking to a guy that...

1) race for Dick Guldstrand in my 68 Corvette with 63 SCCA class wins- I was eeasily the top vette in the nation and never cared to compete at a national level to travel across country. THe one time Brian Hobaugh and his father traveled to my town he got his *** beat- same with the fabled Mark Throton. These high dollar UCAA guys fear me.

You're talking to a guy that...

2) is an accomplished NASCAR crew chief as well as worldly established in mentoring people in chassis dynamics privately- I have also run Nurburgring

You're talking to a guy that...

3) has documented the highest lateral g for a 3rd gen ever on factory 8" wheels

You're talking to a guy that...

4)has designed many parts in the performance world. In fact, I have completely hand built a performance suspenion under my 5000 pound work truck that embarasses most people in their street vettes at autox courses.

My list can go on but I knoiw that covers the point whether I can drive AND engineer, and the fact I know what the heck I am talking about. I encourage, not discourage. I was encouraging you to keep the factory configuration because the platform is not correct. You will find out the hard way. Have a good one and good luck. (As I stated already- but you think Im being an ***...go figure)
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Old 09-18-2017, 03:46 PM   #20
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Re: I'm putting a C4 front suspension into my trans am!!

Non related to the issue with this set up, but is there a thread on thirdgen that shows how to properly build a front suspension for a lowered third gen? What does work if the c4 piece is wrong? I my self was thinking about a 4th gen k member swap a while back, but could not justify it.
Quote:
Originally Posted by SlickTrackGod View Post
You're talking to a guy that...

1) race for Dick Guldstrand in my 68 Corvette with 63 SCCA class wins- I was eeasily the top vette in the nation and never cared to compete at a national level to travel across country. THe one time Brian Hobaugh and his father traveled to my town he got his *** beat- same with the fabled Mark Throton. These high dollar UCAA guys fear me.

You're talking to a guy that...

2) is an accomplished NASCAR crew chief as well as worldly established in mentoring people in chassis dynamics privately- I have also run Nurburgring

You're talking to a guy that...

3) has documented the highest lateral g for a 3rd gen ever on factory 8" wheels

You're talking to a guy that...

4)has designed many parts in the performance world. In fact, I have completely hand built a performance suspenion under my 5000 pound work truck that embarasses most people in their street vettes at autox courses.

My list can go on but I knoiw that covers the point whether I can drive AND engineer, and the fact I know what the heck I am talking about. I encourage, not discourage. I was encouraging you to keep the factory configuration because the platform is not correct. You will find out the hard way. Have a good one and good luck. (As I stated already- but you think Im being an ***...go figure)
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Old 09-18-2017, 05:38 PM   #21
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Re: I'm putting a C4 front suspension into my trans am!!

Quote:
Originally Posted by SlickTrackGod View Post
You're talking to a guy that...

1) race for Dick Guldstrand in my 68 Corvette with 63 SCCA class wins- I was eeasily the top vette in the nation and never cared to compete at a national level to travel across country. THe one time Brian Hobaugh and his father traveled to my town he got his *** beat- same with the fabled Mark Throton. These high dollar UCAA guys fear me.

You're talking to a guy that...

2) is an accomplished NASCAR crew chief as well as worldly established in mentoring people in chassis dynamics privately- I have also run Nurburgring

You're talking to a guy that...

3) has documented the highest lateral g for a 3rd gen ever on factory 8" wheels

You're talking to a guy that...

4)has designed many parts in the performance world. In fact, I have completely hand built a performance suspenion under my 5000 pound work truck that embarasses most people in their street vettes at autox courses.

My list can go on but I knoiw that covers the point whether I can drive AND engineer, and the fact I know what the heck I am talking about. I encourage, not discourage. I was encouraging you to keep the factory configuration because the platform is not correct. You will find out the hard way. Have a good one and good luck. (As I stated already- but you think Im being an ***...go figure)
I'm glad you have the past credentials, however my point still stands that you have never personally done this swap, nor has anybody else. So sure, you can engineer all the details you want on paper, but I have worked for aerospace companies in the past. If theres one thing I do know, it's that when you "engineer" something on a piece of paper, it is quite different than when it actually comes to fruition in the real steel.

But you seem to be missing my main point. This is not a race car and I am not a racer. This swap is for the ONE and only purpose of having tighter and better drivability on the street. Mcpherson suspension in 3rd gens are junk when they are lowered, modified, whatever. You need drop spindles which I don't even believe are made for these cars anymore, and if you want much more than a few degrees of caster, you have to cut the heck out of the strut towers anyways. Lets not forget the fact that they are probably the only vehicle in existence with a gear box mounted to a flimsy unibody instead of a true boxed front frame section. So if you want less flex in the steering system, you're going to have to brace up/gusset the entire front subframe anyways. I have watched the frame rail in these cars flex back and forth 1/8" or more sometimes while sitting still on the ground and just lightly rocking the steering wheel back and forth. The amount of work involved to get the stock mcpherson setup to where I would want it would not be worth it when I can have the SLA setup for the price I paid for it.

Anyways, maybe the way you type just comes across as a bit arrogant, and whether you mean it or not I don't know. But I'm willing to bet that this swap will work very well for what I want it to do.
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Old 09-18-2017, 06:50 PM   #22
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Re: I'm putting a C4 front suspension into my trans am!!

First off let's get this straight. I don't type on here to make best buds with anyone or to be an a****** with anyone. I type facts and I've been known for decades to help people out of my own pocket and my own time for free. I don't sell anything and I shoot from the hip when it comes to people overlooking facts.

now with that said, in my very first post I explain the problem with the swap between the C4 and the factory third gen front suspensions. I even took the time to research the proper numbers and to give you that information. Part of the reason why I was doing this was to help you by double-checking and seeing if what you were doing was feasible and I'd be more than glad to offer advice and help you through this. You chose to come back arrogantly telling me you know what you're doing and it's going in there anyways and that it's not a race car. Well even if it's the most team Streetcar, when you get on the brakes hard in a panic situation on an uneven Road it is going to violently rip the steering wheel out of your hand because of the massive positive scrub radius. The Vets rear platform matches its front platform in track with which means the center with of the front and rear tires as for balance and how things are forced and applied through center of gravity. You're changing that and taking one platform combining it with another one and not understanding how forces are applied especially through scrub radius. Now ask yourself if I was such an a****** why am I taking the time to input all of this into this post in order to help you with information?
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Old 09-18-2017, 06:54 PM   #23
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Re: I'm putting a C4 front suspension into my trans am!!

Also when you talk about your Aerospace fabrication skills and talk about how things done on paper don't always work in the real world? Might you look back up top at my credentials and see where I've been in NASCAR crew chief for over 10 years which means I take other people's designs and tweak them and make them work to that day's environment. I am a specialist at what you just claimed I don't know anything about
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Old 09-18-2017, 06:58 PM   #24
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Re: I'm putting a C4 front suspension into my trans am!!

Man, I am glad you are back living the dreams of most thirdgeners lol.
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Old 09-18-2017, 07:30 PM   #25
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Re: I'm putting a C4 front suspension into my trans am!!

Following....
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Old 09-18-2017, 07:41 PM   #26
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Re: I'm putting a C4 front suspension into my trans am!!

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Man, I am glad you are back living the dreams of most thirdgeners lol.
LOL, I figured it'd been a while since I was on TGO. Wanted to show everyone what I was up to these days.

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First off let's get this straight. I don't type on here to make best buds with anyone or to be an a****** with anyone. I type facts and I've been known for decades to help people out of my own pocket and my own time for free. I don't sell anything and I shoot from the hip when it comes to people overlooking facts.

now with that said, in my very first post I explain the problem with the swap between the C4 and the factory third gen front suspensions. I even took the time to research the proper numbers and to give you that information. Part of the reason why I was doing this was to help you by double-checking and seeing if what you were doing was feasible and I'd be more than glad to offer advice and help you through this. You chose to come back arrogantly telling me you know what you're doing and it's going in there anyways and that it's not a race car. Well even if it's the most team Streetcar, when you get on the brakes hard in a panic situation on an uneven Road it is going to violently rip the steering wheel out of your hand because of the massive positive scrub radius. The Vets rear platform matches its front platform in track with which means the center with of the front and rear tires as for balance and how things are forced and applied through center of gravity. You're changing that and taking one platform combining it with another one and not understanding how forces are applied especially through scrub radius. Now ask yourself if I was such an a****** why am I taking the time to input all of this into this post in order to help you with information?
This front end swap has been done hundreds if not thousands of times into cars with different width rear axles, and like I said, nobody has talked about any ill effects. Just through browsing the pro touring forums, I found many talks about scrub radius. It seems anywhere from 1/2" to 2" is perfect for a RWD car, however there were some saying they had a 3-4" scrub radius and noticed no ill effects on the street. It would appear to me that while a good scrub radius will help the braking performance, it is not an end-all deal breaking measurement. A few people that had closer to 4" of scrub radius said the car drove perfect down the road, during hard cornering, etc. One of the guys was actually an autocross guy who said he had one of the fastest lap times in his group with almost 4" of it.

I am not a suspension pro, nor will I ever claim to be. But I can learn pretty much anything, and I have researched this swap for months. I have not found anybody talking about ill after effects as long as it's installed square and level with the ground.

Quote:
Originally Posted by SlickTrackGod View Post
Also when you talk about your Aerospace fabrication skills and talk about how things done on paper don't always work in the real world? Might you look back up top at my credentials and see where I've been in NASCAR crew chief for over 10 years which means I take other people's designs and tweak them and make them work to that day's environment. I am a specialist at what you just claimed I don't know anything about
I never claimed you didn't know anything about the subject. I simply said you can't know all the details about a swap thats never been done before in a 3rd gen. I'm going to apologize because I think we are both getting off on the wrong foot. I will be 100% going through with this swap though, and if you'd like to offer any other input I will gladly listen.
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Old 09-18-2017, 08:55 PM   #27
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Re: I'm putting a C4 front suspension into my trans am!!

It took me a while to figure out who is SlickTrackGod. Once I did figure it out I began to listen intently. I assume any lack of understanding is my own fault and I need to better listen or ask more questions.

I am an engineering team leader, by the way. One of my skill sets is recognizing experts and utilizing them. You would be surprised how many people cannot do that, even in engineering communities.
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Old 09-19-2017, 12:28 AM   #28
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Re: I'm putting a C4 front suspension into my trans am!!

STiG is a FreakinGoodTimeDuracellBunny.
OR aka Michael Andretti clone (hehehe) - 14 years ago, whew!

Seriously though, I checked the SpeedTech Extreme clip and it starts at $7100 plus you have to add options! w/out install!

WhitedevilTA - Go for it. We're here to learn from each other, even each others' mistakes. Not pre-judging your project as a mistake. If you have the desire, and can live with a mistake if that's the result, prove everyone wrong. IMHO, the benefit is little, and the risk to the car is great (nice paint, by the way). I'm not the pioneer type on something this big, but someone has to be. Go for it.
A little humility goes a long way, until you can say, 'I told you so.'
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Old 09-19-2017, 01:06 AM   #29
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Re: I'm putting a C4 front suspension into my trans am!!

Where the heck did you get that old pic of me from? I had a goatee when I was about 30 (20 years ago.)


Whitedevil, I am always here to help with advice. Trust me the srcub will be about 2 3/4" and will in fact be noticible- that is why I calculated it for you to see if what you are doing will have flaws. As long as you undersd this then is your choice. Just giving info and not trying to discourage if that is what you are set on doing. You can run a little more aggressive camber so the tires run more on the inside edges to help with braking forces.

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Old 09-19-2017, 01:13 AM   #30
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Re: I'm putting a C4 front suspension into my trans am!!

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STiG is a FreakinGoodTimeDuracellBunny.
OR aka Michael Andretti clone (hehehe) - 14 years ago, whew!

Seriously though, I checked the SpeedTech Extreme clip and it starts at $7100 plus you have to add options! w/out install!

WhitedevilTA - Go for it. We're here to learn from each other, even each others' mistakes. Not pre-judging your project as a mistake. If you have the desire, and can live with a mistake if that's the result, prove everyone wrong. IMHO, the benefit is little, and the risk to the car is great (nice paint, by the way). I'm not the pioneer type on something this big, but someone has to be. Go for it.
A little humility goes a long way, until you can say, 'I told you so.'
Holy crap lol, that thing better be gold plated for that price!! I'm honestly not expecting the car to suddenly feel like an F1 car in the handling dept. All I really want out of this swap is tighter turning and the ability to better control a 275 front tire on a wider wheel during every day street driving. If it does that, it will be 100% worth the effort to me. I've come up with a plan to modify my frame rail in a way where there will be box steel welded to it to mount the vette suspension, but I will not be removing any of the lower section with the bolt holes for the factory K-member. If I absolutely had to, I could return the car back to the factory type suspension relatively easily, but I would have to run a coilover setup instead of the factory style coil spring due to the fender well modifications needed. We'll see how it goes. I'm extremely optimistic going into it!
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Old 09-19-2017, 01:19 AM   #31
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Re: I'm putting a C4 front suspension into my trans am!!

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Whitedevil, I am always here to help with advice. Trust me the srcub will be about 2 3/4" and will in fact be noticible- that is why I calculated it for you to see if what you are doing will have flaws. As long as you undersd this then is your choice. Just giving info and not trying to discourage if that is what you are set on doing. You can run a little more aggressive camber so the tires run more on the inside edges to help with braking forces.
I'm curious now about scrub radius details. How exactly did you calculate it, and what wheel size/offset did you use? I do run aftermarket custom size 17x9 front wheels so now I am genuinely curious if my aftermarket wheels will change that factor. I honestly am not even 100% sure I can run my current wheels if the vette suspension is slightly wider, which would mean I'd need to get a new set of front wheels. I'm thinking if that turns out to be the case, I could always size the wheels to minimize the scrub radius issue.
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Old 09-19-2017, 01:39 AM   #32
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Re: I'm putting a C4 front suspension into my trans am!!

Here's a more appropriate pic for the thread(No one wants a half naked guy sitting on his sofa...lol I erased the spontaneous self portrait I posted above). I was in Istanbul Turkey a little over month ago with Berk and Serdar shaking down the Big Block RamJet502 1990 Trans Am. I help people all over the world with free advice and I often get to go play and have fun mentoring people....for free. TI am the tall one on the passenger side, Berk up front, and Serdar on right. This is at an F1 circuit in Istanbul. We had just got back into Turkey from Nurburgring a week prior.
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Old 09-19-2017, 01:52 AM   #33
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Re: I'm putting a C4 front suspension into my trans am!!

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I'm curious now about scrub radius details. How exactly did you calculate it, and what wheel size/offset did you use? I do run aftermarket custom size 17x9 front wheels so now I am genuinely curious if my aftermarket wheels will change that factor. I honestly am not even 100% sure I can run my current wheels if the vette suspension is slightly wider, which would mean I'd need to get a new set of front wheels. I'm thinking if that turns out to be the case, I could always size the wheels to minimize the scrub radius issue.
The Vette suspension is NOT slightly wider. It is narrower. The hub faces are wider, but the track width is measured at the center of the tire contact patch, not the outside edge.

THe Vette overall width is 71 and the 3rd gen overall width is 72 You will be 1 narrower (I am talking 89-96 cars, not the narrower 84-88)

Scrub radius is measured by drawing an imaginary line from the upper ball joint through the lower ball joint onto the ground. Where this hits the ground is the pivot point of the turning setup. Where the center line of the tire contact patch is outside of this is how much distance the positive scrub radius is.

Now there are factors here I will go over again for you (I already addressed them up top this thread) The Vette front end runs a negative offset wheel- meaning the wheel reaches back over the suspension towards the centerline of the car. The Vette also uses a wider factory 9.5" wheel so taking into account for the plus .75" which is half that width increase to center compared to a factory 8" 3rd gen wheel...plus again the narrower track width by almost 2" (half that on one side is 1") you have a combined total of +1.75 more scrub on each side if you are only running an 8" wheel. Run a wider one sitting more outboard like many people do with a thirdgen and you will sit the scrub out another 1/4 to 1/2" more going to 3" scrub range when you add the original 3rd gen scrub of +1" aprox.

Now formula wise it is a long known fact in racing chassis building that you want to keep the scrub within 20% of the tire width. On an 10" wheel that is 2" max on the ground pivot point from the centerline of the contact patch.- but should be less.

I have driven many many many 3 gens in my life both on street and tracking them. Most track cars have massive scrub with wide tires added outboard (since no room inboard) and I have fought the wheel every time driving one set up like this. (Not going to name names- Ive talked to you people in private)

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Old 09-19-2017, 02:07 AM   #34
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Re: I'm putting a C4 front suspension into my trans am!!

I use a 255 tire on my 17x9 rim. I don't have any of the wondering you talk about and I still have the 30 year old steering box. Getting rid of the rag joint is what did it. That and a good alignment. One of these days I'll probably get a Turn One box and power steering pump.

You have a very nice car. Can't figure out why you're going to hack it up. A 275 tire is going to grab road ruts regardless.
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Old 09-19-2017, 02:15 AM   #35
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Re: I'm putting a C4 front suspension into my trans am!!

Lets now focus in on just the wheel The tire width on an 8" wheel is aprox an 8" contact patch so the centerline is right in the middle at 4". If coming from center line of the car towards the center of tire starts at 0 on inside edge of contact patch and 8" on outside edge, the scrub pivot point on the ground which the tire rotates on is at 1.25" from the inside edge THis means you have 6 3/4" on the ouitside edge of the pivot.

Now apply road force transmitting through this with the scrub point being the fulcrum, you can see how if a wheel hits a bump in the road on the ouside edge of lets say the drivers LF wheel the force will push the outer edge of the tire backwards causing unwanted steering force to be transmitted into the outer dominant side of the fulcrum- this will want to violently rip the steering wheel out of your hands. It is applied leverage much greater outside the balanced center fulcrum point- which if this hits the bump the steering stays straight if applied most directly at the pivot.

You also have other issues with tracking of front and rear wheels when braking is applied in lateral forces, but that is not as critical but does in fact still comes into play Both together can really cause issues. Your rear track centerline will probably be about 4" outside the front scrub which tightens the car under braking and loosens the car under throttle into and exiting corners. The front C4 and rear 3rd gen are different platforms in chassis dynamics geometry- they are not compatible in widths
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Old 09-19-2017, 02:19 AM   #36
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Re: I'm putting a C4 front suspension into my trans am!!

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I use a 255 tire on my 17x9 rim. I don't have any of the wondering you talk about and I still have the 30 year old steering box. Getting rid of the rag joint is what did it. That and a good alignment. One of these days I'll probably get a Turn One box and power steering pump.

You have a very nice car. Can't figure out why you're going to hack it up. A 275 tire is going to grab road ruts regardless.
A 255 tire on a 9" wheel is a 9" contact patch. Your scrub has moved inward to less then 1 so you are only at about 5% scrub ratio- far less then 20%. Even though your wheel is slightly wider overall track width from outside tire edges, your centerline track width closed together with a 0 offset wheel from the factory +16mm offset.

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Old 09-19-2017, 02:40 AM   #37
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Re: I'm putting a C4 front suspension into my trans am!!

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Where the heck did you get that old pic of me from? I had a goatee when I was about 30 (20 years ago.)
https://www.thirdgen.org/forums/susp...t-want-my.html

Berk is staggered with an 8" up front, if I recall. 245 fr and 275 rr on 18
's?
Been considering that with 17's - but I've always been a square guy. I am considering though. 245/275 is not that bad.

QwkTrip -
I did the turn one box (12:1, 670 series) and LS2 flow matched pump (little thing was $395) last year.
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Old 09-19-2017, 02:44 AM   #38
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Re: I'm putting a C4 front suspension into my trans am!!

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https://www.thirdgen.org/forums/susp...t-want-my.html

Berk is staggered with an 8" up front, if I recall. 245 fr and 275 rr on 18
's?
Been considering that with 17's - but I've always been a square guy. I am considering though. 245/275 is not that bad.

QwkTrip -
I did the turn one box (12:1, 670 series) and LS2 flow matched pump (little thing was $395) last year.
You know I can;t recall now what he has. I think he is on 19" wheels 8.5" fronts and rears. Car has changed a few times. Had to get some ground clearance with the big block oil pan so he upped the rim size to fit the wheel wells.

I need to look on here for more old photos Ive lost years ago. never thought of searching my old screen names for them to see what is on here.
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Old 09-19-2017, 02:53 AM   #39
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Re: I'm putting a C4 front suspension into my trans am!!

My front end is pretty well-behaved. However, the rear is a real mess and severely limits what I can do. I screwed up my car by overpowering it. I have been relegated to drag radials and now the car can't do anything well. If I could get reasonable traction with good handling tires then I would love to go back to a handling setup. Drag radials are not very fun to live with and I ruin them fast. 2000 miles and the third pair is sitting in the garage waiting to be mounted.
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Old 09-19-2017, 02:56 AM   #40
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Re: I'm putting a C4 front suspension into my trans am!!

He must have changed, as I asked him once before.
I've always thought I could get 8.5" with the drop spindles, but didn't know if I'd end up with an odd size tire, or something that could get discontinued.

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Old 09-21-2017, 08:40 PM   #41
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Re: I'm putting a C4 front suspension into my trans am!!

Got my exact suspension centerline figured out today and "set in concrete" lol. What an absolute nightmare. The frame rails on these cars make me wonder what went through GM's mind when designing them. There is not one single measurement that matches on either frame rail, and the factory suspension arms are not equally spaced from the K-member mounting points. My head hurts, but I got it done with painful amounts of math and plumb bob lines. Anyways, I'll post up the info for anybody that may be interested. Heres a few finished pics and my chicken scratch sheet.
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Old 09-22-2017, 07:51 PM   #42
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Re: I'm putting a C4 front suspension into my trans am!!

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Old 09-23-2017, 12:07 AM   #43
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Re: I'm putting a C4 front suspension into my trans am!!

Tore my rotator cuff 4 months ago throwing a football back to a few neighborhood kids- Went pop. Very painful rehab but work it with light weights and keep the range of movement. Hurts like hell when sleeping.

Anyways, weant to give you a few tips of advice on stringing the car for straightness.

What is very important is the suspension pick-up points or what is refered to as the Suspension "ears". Since you took the k-member off you do not have reference to the front ears, but what you did so far is great. What I would jighly recommend before you go any further is to drop the plumbob off each rear chassis LCA mount and draw a perpendicular line (lateral line) to the centerline of the car. Draw it on the ground. Then find the centerline of the rear section of car.

Now with that rear centerline mark, connect the dots of the front suspension centerline to the rear with a chalkline (or draw if out- chalk is erasable). Now off that full chassis length centerline of the vehicle through the front and rear suspension, you want to check the 90* perpendicular of the rear chassis ears using Pythagorean's Theorem (3*+4*=5*). This will guarantee the chassis is square. THen once you verify this is perpendicular you can reference front he rear lateral suspension line up to the front fender poist and figure the squareness of the front frame rails to the rear of the car.

Lastly to triple check things. You take two diagonal measurements - one from left rear ear to right front fixed point , and vica versa to check for diagonal symmetry.

Dean
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Old 09-23-2017, 03:21 AM   #44
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Re: I'm putting a C4 front suspension into my trans am!!

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Originally Posted by SlickTrackGod View Post
Tore my rotator cuff 4 months ago throwing a football back to a few neighborhood kids- Went pop. Very painful rehab but work it with light weights and keep the range of movement. Hurts like hell when sleeping.

Anyways, weant to give you a few tips of advice on stringing the car for straightness.

What is very important is the suspension pick-up points or what is refered to as the Suspension "ears". Since you took the k-member off you do not have reference to the front ears, but what you did so far is great. What I would jighly recommend before you go any further is to drop the plumbob off each rear chassis LCA mount and draw a perpendicular line (lateral line) to the centerline of the car. Draw it on the ground. Then find the centerline of the rear section of car.

Now with that rear centerline mark, connect the dots of the front suspension centerline to the rear with a chalkline (or draw if out- chalk is erasable). Now off that full chassis length centerline of the vehicle through the front and rear suspension, you want to check the 90* perpendicular of the rear chassis ears using Pythagorean's Theorem (3*+4*=5*). This will guarantee the chassis is square. THen once you verify this is perpendicular you can reference front he rear lateral suspension line up to the front fender poist and figure the squareness of the front frame rails to the rear of the car.

Lastly to triple check things. You take two diagonal measurements - one from left rear ear to right front fixed point , and vica versa to check for diagonal symmetry.

Dean
I believe that's exactly what I tore. Luckily it wasn't a serious tear because I still had a full range of arm movement, but man did it hurt like heck lifting it over half way or putting any kind of pressure on it. I would say I'm at about 80% now. It feels good enough to move up and down with no pain, and only gives me slight issue when holding something with some weight in certain positions. But man you aren't kidding about painful sleeping! For a day or two I was almost teary eyed trying to go to sleep.

That's a great idea about measuring up the rear and comparing it to the front measurements. I may be able to get that taken care of this weekend to really ensure I'm all set.

I also have a question for you. Unfortunately I have to relocate the rack quite a bit for it to fit under the oil pan. It seems the only solution I can come up with is to move it backwards about 3/4" and then down 2". I know I can run a 2" drop bump steer kit to keep the tie rods level at ride height, but in your opinion will moving it backwards 3/4" hurt the steering geometry much? I'm thinking it'll barely be noticeable but I want to be sure.
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Old 09-23-2017, 09:55 AM   #45
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Re: I'm putting a C4 front suspension into my trans am!!

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I also have a question for you. Unfortunately I have to relocate the rack quite a bit for it to fit under the oil pan. It seems the only solution I can come up with is to move it backwards about 3/4" and then down 2". I know I can run a 2" drop bump steer kit to keep the tie rods level at ride height, but in your opinion will moving it backwards 3/4" hurt the steering geometry much? I'm thinking it'll barely be noticeable but I want to be sure.
Moving it back and lengthening the tie rods slightly should in fact actually help increase the Ackerman which is what is needed. The optimum amount moving it backwards is about 5/8" and then it will start to loose ackerman again moving it more then this. THe two inches down will have to be met with the spindle arms having bump steer kits install to lower those mounts to match. THe issue you will probably have here is wheel contact at the lowered outer tie rod positions. Hopefully not but this is an issue on third gens also with drop spindles.
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Old 09-23-2017, 12:04 PM   #46
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Re: I'm putting a C4 front suspension into my trans am!!

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Moving it back and lengthening the tie rods slightly should in fact actually help increase the Ackerman which is what is needed. The optimum amount moving it backwards is about 5/8" and then it will start to loose ackerman again moving it more then this. THe two inches down will have to be met with the spindle arms having bump steer kits install to lower those mounts to match. THe issue you will probably have here is wheel contact at the lowered outer tie rod positions. Hopefully not but this is an issue on third gens also with drop spindles.
Well that gives m some relief then. After all, a major part of doing this is for the rack lol. I don't believe the dropped tie rods will interfere with rim clearance at all because the C4 steering arms sit much higher than the factory 3rd gen ones in relation to the hub center. Dropping them 2" should still put them inside the wheel with room to spare. But thank you for the info!
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Old 09-27-2017, 08:39 PM   #47
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Re: I'm putting a C4 front suspension into my trans am!!

Gentlemen, it's bolted in It's currently mounted on temporary adapter brackets holding it to my existing K-member mounting holes, but it should be in the exact centered location according to my measurements. Ran out of time today but tomorrow I may try to cut some holes in the fender wells and get the upper A-arms mocked up so I can really get a feel for how everything is going to line up. But my initial measurements are solid and I am pretty confident it's exactly where it should be.
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Old 09-27-2017, 09:25 PM   #48
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Re: I'm putting a C4 front suspension into my trans am!!

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Originally Posted by whitedevilTA View Post
Gentlemen, it's bolted in It's currently mounted on temporary adapter brackets holding it to my existing K-member mounting holes, but it should be in the exact centered location according to my measurements. Ran out of time today but tomorrow I may try to cut some holes in the fender wells and get the upper A-arms mocked up so I can really get a feel for how everything is going to line up. But my initial measurements are solid and I am pretty confident it's exactly where it should be.

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Old 09-28-2017, 06:51 PM   #49
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Re: I'm putting a C4 front suspension into my trans am!!

This is a fascinating project. Congrats on the progress thus far.
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Old 09-29-2017, 02:55 PM   #50
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Re: I'm putting a C4 front suspension into my trans am!!

Definitely interested to see what you do about the upper control arm situation
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