Suspension and Chassis Questions about your suspension? Need chassis advice?

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

Old 10-23-2017, 12:42 PM
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Re: I'm putting a C4 front suspension into my trans am!!

Originally Posted by soloc4 View Post
Hey Rob, your progress looks great. If it helps, I'm using a 450# spring on the front of mine from Viking. Both RideTech and Viking have calculators on their websites. I assumed a 3300 car with a 52/48 weight distribution. You're making great progress, keep up the good work.
Thanks for the info! I tried the calculator last night on ridetechs website and it was not working. Checked it out again just now and I was able to plug in my info.

Originally Posted by SlickTrackGod View Post
Most people with C4 Vettes that do coilover conversions run 400front/275 rear. #rd gen strut coilover packages come in a a slightly less leveraged point so they run a liittle lower at 350-400 range. With that said, my guess would be 425-450 range. I would tend to go 450 and leave a smaller sway bar .

As for caster, as long as you have adjustment in the range to get it down to at least 7 then you are good with the a-arm angles and the 450 spring rate- keep in mind if the a0-arm is slightly more up on the front ear mount compared to the rear ear then the angle of attack when the car hits a bump will compress the shock with just a slight tad more leverage due to angle. 10* is getting high. Factory specs is 4-6^ for those years with performance settings at 6*-7*. You may want to shim the k-member a little more forward to reduce the angle. Too much caster can give you bump steer problems as well but that is only if it is misaligning with the rack- since everything is tilted back then that does not apply. Agressive caster brings outer tie rods up AND BACK, not just up.
I was able to get the calculator on ridetechs webside to work (it was down last night) and it gave me a spring rate of 425 lbs for "performance street driving" and 450 lbs for "racing." I much prefer a performance street driving style suspension, but I may call up ridetech and get their opinion as well. Granted, the difference between the two springs is probably not overly noticeable IMO, and the shocks are adjustable as well to dial it in a bit more to my liking.

As for caster, at this point I'm thinking I may just see what it is once the car is together and on the ground, because the way I have the crossmember positioned will give me the exact 14.5* upper A-arm angle at my ride height and rake. I would think that should also put the caster right where it needs to be, and I'm assuming with alignment shims it could be fine tuned even more. If it came down to it, it would not be overly difficult to slightly tilt the crossmember even after it's all together with how it mounts to the car.

But thanks a lot for the help so far. Much appreciated! Glad your recommendations closely match the spring rate calculator numbers. Makes me feel confident about what I need.
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Old 10-23-2017, 10:04 PM
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Re: I'm putting a C4 front suspension into my trans am!!

My concern about Caster is the old C4 guys I knew and drove some of their cars back in the day use to run lower caster for AutoX when they increased static camber setting. -I will say that again- Yes, they would DECREASE caster and run about 3-4* positive caster to get the footprint onto the ground with wide tires on tight corners. Running larger tracks at higher speeds (more of road courses like Willow Springs etc) they would leave less static camber and run higher caster to 6-7*.

If you end up having issues with scrub radius and I want you to try and move the camber higher, you will want to have the option to also lower caster if that ends up being the need for more negative camber to get the center of the tire contact patch towards the zero scrub point.

SO now you understand my mind thought and possible concern that you may have too high a range for a bandaid fix for the other possible issue. The Vette steering racks were tight and powerful enough in effort to overcome heavy steering on hard braking tight corners of autox, so I am hoping the initial "possible scrub problem" I first talked about in this post early on is overcome with steering resistance force - thus this would not be necessary. I am just looking for more tools for setup tuning in case this does become necessary.

Last edited by SlickTrackGod; 10-23-2017 at 10:19 PM.
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Old 10-24-2017, 02:45 PM
  #103  
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Re: I'm putting a C4 front suspension into my trans am!!

Originally Posted by SlickTrackGod View Post
My concern about Caster is the old C4 guys I knew and drove some of their cars back in the day use to run lower caster for AutoX when they increased static camber setting. -I will say that again- Yes, they would DECREASE caster and run about 3-4* positive caster to get the footprint onto the ground with wide tires on tight corners. Running larger tracks at higher speeds (more of road courses like Willow Springs etc) they would leave less static camber and run higher caster to 6-7*.

If you end up having issues with scrub radius and I want you to try and move the camber higher, you will want to have the option to also lower caster if that ends up being the need for more negative camber to get the center of the tire contact patch towards the zero scrub point.

SO now you understand my mind thought and possible concern that you may have too high a range for a bandaid fix for the other possible issue. The Vette steering racks were tight and powerful enough in effort to overcome heavy steering on hard braking tight corners of autox, so I am hoping the initial "possible scrub problem" I first talked about in this post early on is overcome with steering resistance force - thus this would not be necessary. I am just looking for more tools for setup tuning in case this does become necessary.
Just did a bit of research on this topic. It appears that a good general "performance street" setting is anywhere from 5-7* caster, and .5-1* negative camber. The way the suspension is currently installed with no alignment shims, it's at roughly 1-1.5* negative camber, and 10* caster (car level, not at my ride position.) Granted, I'm taking very crude measurements with an angle finder and a piece of flat steel, so there could be a degree off here or there. I read that adding a shim to the rear upper CA bolt but not the front will decrease caster, but add positive camber. I'm going to play around with some shims and see how much it changes by adding them to the rear CA bolt only. If I can get down to 6-7* caster and .5* negative camber, I'd be very happy with that in a street car. As for the scrub radius, I guess time will tell if that will in fact be an issue I feel or not, and if so, I will have to tweak the suspension a bit. To be honest, I am in no way assuming this thing will be perfect right from the first drive. I have every intention of making slight changes here and there as I go and experiment with it.

I do appreciate you bringing this topic up though, because to be honest, it was sort of in the back of my mind with all the other fabricating going on!

Last edited by whitedevilTA; 10-24-2017 at 02:48 PM.
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Old 10-24-2017, 08:20 PM
  #104  
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Re: I'm putting a C4 front suspension into my trans am!!

You can also swap the upper control arm spacers front to back and change the caster dramatically without changing camber (large spacer rear, small forward to decrease caster). You can play around with this after the fabrication is finished.
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Old 10-24-2017, 09:59 PM
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Re: I'm putting a C4 front suspension into my trans am!!

Finished making the mounting plates for the lower mounting points on the C4 crossmember. They aren't welded up yet because I figured having the room down there would be nice for when I notch the frame rail for coilover clearance. Also included a picture that shows the side plate mounts a bit better than in my video. Starting to take some real shape!

Originally Posted by soloc4 View Post
You can also swap the upper control arm spacers front to back and change the caster dramatically without changing camber (large spacer rear, small forward to decrease caster). You can play around with this after the fabrication is finished.
That's great to know! I honestly never even thought about that. I'd bet that if I used the same size spacers on the front and rear (as opposed to the offset sizes), it would knock the caster number down at least a few degrees. I always liked having plenty of caster in a street car for high speed stability and steering wheel return, but I guess I'll have to fine tune everything when it's together until I get it where I like the way it feels.
Attached Thumbnails I'm putting a C4 front suspension into my trans am!!-dsc02424.jpg   I'm putting a C4 front suspension into my trans am!!-dsc02426.jpg  
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Old 10-26-2017, 11:04 AM
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Re: I'm putting a C4 front suspension into my trans am!!

Need some help concerning coilover selection. Originally I was set on a coilover with the following specs:

12.5" ride height
14.2" extended
10.1" compressed
(4.1" total stroke)
10" spring

However, My suspension will not have the travel to make use of the full range of that shock, and because the coilover will be mounted to the vette setup at a 25* angle, I'll get more travel out of a shorter shock anyways. After reconsidering, I'm wondering if I can go shorter with no ill effects. The room I have to work with between the upper A-arm would MUCH favor a shorter shock/spring combo and it seems many of the C4 vette guys also run the shorter setup when using coilovers. The one I now have in mind is:

11.5" ride height
13" extended
9.4" collapsed
(3.6" total stroke)
8" spring

So, am I really losing anything by going to the shorter setup considering it would still allow the suspension to travel it's full range? Like I said, space constraints greatly favor the shorter combo.
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Old 10-26-2017, 11:46 AM
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Re: I'm putting a C4 front suspension into my trans am!!

Food for thought- this is just my opinion by Ill give you my mindset when install shocks.

Shocks are not something I worry about "unsprung weight wise" when it comes to length, I do however try to always buy monotube shocks that I can run upside down for less unsprung weight of the fluid body.

1) I try to run the longest shock I can so the piston is deep inside the body of the shock furthest from the rod entry point into the shock body- Why? Stablity of the entire assembly when it pertains to side leverage of forces on the seals.

2) I like to run the largest and longest body shock i can for more fluid volume so the shock runs a cool as possible.

3) more angle means higher shock valve damper settings- which in turn means more heat and more wear over lifetime of the shock. (reason I run two shocks on every wheel of my Vetruck (it weighs 5000lbs) I found two shocks running lower settings will last 4x as long as one shock set very high in damper force.

Really the best answer most of the time is "what fits best?" Room is usually an issue using coilovers through upper control arms. Try and always place adjusters where you can get to them.
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Old 10-26-2017, 12:14 PM
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Re: I'm putting a C4 front suspension into my trans am!!

I agree with everything STG has stated, there is one other thing to remember, a shorter spring will ride harsher than a longer spring. Unfortunately, there are compromises to be made throughout a project like this.
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Old 10-26-2017, 12:41 PM
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Re: I'm putting a C4 front suspension into my trans am!!

Thank you both for the great info. Both choices will "fit," however with the longer combo, the spring will be between the upper A arm at full droop and have about 1/4" clearance at both sides of the arm. The longer spring will also be just at the point where it's constantly going between the upper A-arm during bumps. With the shorter setup, the spring will be slightly below the upper A-arm even at full droop and will allow plenty of wiggle room. At this point I'm willing to sacrifice some driving comfort and go with the shorter spring just for the peace of mind that it will fit much better. Plus, the car only gets driven locally on the street 99% of the time, so fatigue isn't a huge concern of mine. Ridetech uses very high quality hyperco springs, so I'm thinking if I get the spring rate on the money it will still perofrm and drive very well.

Again, thanks a ton for the help and info
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Old 10-28-2017, 01:33 AM
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Re: I'm putting a C4 front suspension into my trans am!!

Really starting to look like a frame rail now. Chauking the drivers side up as done...minus some sheet metal work to dress it up. MAY add a few gussets from the main crossmember plate to the frame rail just for added support, but probably not necessary.
Attached Thumbnails I'm putting a C4 front suspension into my trans am!!-dsc02439.jpg   I'm putting a C4 front suspension into my trans am!!-dsc02440.jpg   I'm putting a C4 front suspension into my trans am!!-dsc02442.jpg  
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Old 10-30-2017, 01:14 AM
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Re: I'm putting a C4 front suspension into my trans am!!

New vid, and pics!

Ended up adding a gusset to reinforce the top area of the side plate because if I yanked on it hard, I could see it just slightly flex. Now it's solid as a rock. Also plug welded the bottom pinch seam and gave it a coating of black paint to protect it. Last thing to do is the sheet metal work.

Attached Thumbnails I'm putting a C4 front suspension into my trans am!!-dsc02444.jpg   I'm putting a C4 front suspension into my trans am!!-dsc02446.jpg  
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Old 11-07-2017, 12:41 AM
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Re: I'm putting a C4 front suspension into my trans am!!

Passenger frame rail 100% done. Made block off plates for the front and rear of the lower mount area out of 1/8" plate and finished off all the rough areas with 16 gauge sheet metal. So pumped with how this came out! Finally looks like a frame rail and not some metal square stock welded between my old rails!! Should have the drivers side finished off tomorrow as well, and then moving on to modifying the vette crossmember for rack clearance.
Attached Thumbnails I'm putting a C4 front suspension into my trans am!!-dsc02471.jpg   I'm putting a C4 front suspension into my trans am!!-dsc02472.jpg   I'm putting a C4 front suspension into my trans am!!-dsc02475.jpg  
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Old 11-08-2017, 08:19 PM
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Re: I'm putting a C4 front suspension into my trans am!!

It's nice when the coilovers have the adjustment **** inverted - made to run upside down.
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Old 11-09-2017, 12:20 AM
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Re: I'm putting a C4 front suspension into my trans am!!

Originally Posted by TEDSgrad View Post
It's nice when the coilovers have the adjustment **** inverted - made to run upside down.
Are those yours? I think ride tech is one of the best on the market currently. I heard they are "meant" to be installed spring side up, but they claim it honestly doesn't matter either way because they are a gas shock. Once I get my set I'll have to figure out the best orientation to mount them in.
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Old 11-09-2017, 12:26 AM
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Re: I'm putting a C4 front suspension into my trans am!!

Yes, they are attached to the Mark Williams 12-bolt.
HQ6110
Range - 14"
Collapsed - 11.34"
Extended - 16.5"
12" Spring #250

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Old 11-14-2017, 06:58 PM
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Re: I'm putting a C4 front suspension into my trans am!!

Been frigid here in CT with the temp being 28*-35* during the day, so motivation has not been very great. But I did end up finishing up the oil pan notch in the crossmember today and snapped a few pics of the completed drivers side frame rail.

Only major fab left now is cutting off the front section of the vette crossmember and moving the rack to where it'll fit. Just haven't come up with a good way of doing it and retaining the correct location of the lower control arm mounts. I was thinking of making a jig of some sort, but just don't feel like investing that much time into something like that at the moment. Like I said, motivation is low with the weather lol.
Attached Thumbnails I'm putting a C4 front suspension into my trans am!!-dsc02485.jpg   I'm putting a C4 front suspension into my trans am!!-dsc02483.jpg   I'm putting a C4 front suspension into my trans am!!-dsc02479.jpg  
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Old 11-15-2017, 07:32 AM
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Re: I'm putting a C4 front suspension into my trans am!!

This is sooo cool, I'm lucky to get the motivation to clean the air filter and change the oil these days. (family and house remodel take a lot of my time!)
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Old 11-17-2017, 07:58 AM
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Re: I'm putting a C4 front suspension into my trans am!!

Just set up the oil heater in the attached garage this morning. I'm only about 45 days behind on being ready for fall!
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Old 11-19-2017, 12:19 AM
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Re: I'm putting a C4 front suspension into my trans am!!

Originally Posted by TTOP350 View Post
This is sooo cool, I'm lucky to get the motivation to clean the air filter and change the oil these days. (family and house remodel take a lot of my time!)
Thank you! In the path my life took, I currently have no wife (or even GF at the moment lol) and no children, so I really have a ton of time to sink into the car to keep me busy. And actually, I was unemployed for a bit up until recently as well. I was just hired by an aerospace company as a machinist, so I am pumped at the new opportunity and the pay, but also a bit bummed because now working on the car will slow down a bit. Either way, it'll be done hopefully by spring so I can dial it in and enjoy it!

Originally Posted by DynoDave43 View Post
Just set up the oil heater in the attached garage this morning. I'm only about 45 days behind on being ready for fall!
Haha, you and me both. I haven't even blown the dust off my propane heater to dig it out of the basement yet. Although at this rate it will happen very soon.
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Old 11-19-2017, 12:13 PM
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Re: I'm putting a C4 front suspension into my trans am!!

I have a concern that arose recently that I'd like some input on regarding properly set up steering systems. I have to drop the corvette rack down about 2" and back about 1" to fit under my oil pan. Moving it back 1" should be fine as far as geometry is concerned, but I just realized during mock up that the inner rack pivot points will no longer follow the line between the upper and lower A-arm bushings with it being 2" lower. Where I will need to locate the rack, those inner pivots will protrude roughly 1/2" past that imaginary line on each side, and I'm curious if that's going to cause a big issue with bump steer?

The factory vette rack appears to be 26" from inner pivot to inner pivot, and I have seen that a mustang rack is 24.5" inner pivot to inner pivot. That would get me much closer to the magic line, but I wanted to try to use the vette rack if possible. I want this to be done right so is there any way to tell how bump steer will be, or is it one of those things where I'd have to get it all together and physically check it first? Would really hate to fab up rack mounts only to have to chop them off to go with a different rack.
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Old 11-20-2017, 10:04 AM
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Re: I'm putting a C4 front suspension into my trans am!!

No you are not causing changed issues as long as you do what was priviously talked about in spacing the spindle attachments down the same 2 ".

I'll explain why and what is confusing you. The spindle steering arm is fixed in a ride location in relation to the C4 k-member. You are still using both together and the length of the steering rack was positioned to the k-member with the appropriate length to be parallel to that spindle. If the upper control arm is lets say for sake of easy numbers argument 10" long and the a-arm is 12" long- and height wise they are 10" apart- then you have a spindle that rides near the middle line height wise of those the tie rod needs to be 11" long.

Now by dropping the rack 2" and then going across those 11" tie rods...if you did not drop that spindle mount vertically downward the tie rod would have to angle upward in geometry lengthening it to get back up to that height and thus would be probably more like 12" to span a lateral distance of 11". Not a problem until it starts into dynamic motion in wheel assembly compression the longer tie rod will not follow the arc of the two suspension arms.

If you put the tie rod back into the position of lateral static arc it is designed to be in in union with that k member and suspension and simply use vertical links to connect back up to the spindle heights then you are fine. Everything is in relation. Move it down 8" then move then use 8" vertical links to the spindle, etc

Last edited by SlickTrackGod; 11-20-2017 at 10:07 AM.
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Old 11-20-2017, 10:20 AM
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Re: I'm putting a C4 front suspension into my trans am!!

Here- I grabbed a drawing and modified it for explanation.

Red is the same tie rod length just lowered 2" in the new parallel position to the old height. Purple circle shows the 90* vertical solid link to the spindle (the longer this is however the weaker it becomes to leverage force and can be dangerous).

The yellow is the old rack position moved downward tot he new 2" lower position.

The red tierod stays the same length because the original spindle height position is still the same height relation with the solid vertical link to where it will then push laterally.

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Old 11-20-2017, 10:34 AM
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Re: I'm putting a C4 front suspension into my trans am!!

Now of course this example would be bad because the arcs are different paths and the steering would toe in under wheel assembly compression.

Now in hopes not to confuse you any further but to explain problems that already exist in steering geometry, we need to consider the best left right piviot leverage point of the wheel would be center tire height off the ground of course. Also take into account 3D wise the caster angle and how that vertical center height changes in caster line swing of the spindle mount point. Engineers already had to lower the spindle from center tire height in order to get under the chassis and swaybar components AND as you are seeing the engine. The steering geometry is already at a disadvantage from the factory due to this and is why some cars suffer for proper Ackerman build (toe gain in steering angle). Rear engine cars are great for this aspect because they have much more room for a centered height steering arm off the spindle without a drop bandaid position for clearance.


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Old 11-20-2017, 10:57 AM
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Re: I'm putting a C4 front suspension into my trans am!!

Now in a perfect world this is pretty much what you would want to pinpoint to the center of the wheel (pink line) and position the spindle steering arm at this raised height from where the original on this example is shown. You would then have to also raise the steering rack up which we all know there is no room. now you see what GM engineers face.

One of the reasons the C8 Vette is going mid engine.


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Old 11-20-2017, 11:11 AM
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Re: I'm putting a C4 front suspension into my trans am!!

Well that just gave me a major sigh of relief! I honestly think I was just way overthinking things. I had the original idea and design down pat and then recently started to modify the cross member which brought that concern up. I figured I would bring it up because part of the reason for doing this swap is to improve on the steering feel, so that's something I'd like to get right!

Through my research last night, I did actually find a drawing similar to the one you posted (Great art work by the way! lol) that more or less sort of showed how it would work without having the rack pivots fall on that bushing line. It's great to get a confirmation on here as well. Now I feel like I can continue forward. Thanks a bunch for clearing that up for me. I'm very visual so the second I looked at your drawing I understood why I shouldn't have any issue.
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Old 11-20-2017, 05:05 PM
  #126  
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Re: I'm putting a C4 front suspension into my trans am!!

We danced around this a little on FB, I'm in the "this isn't going to be handling improvement you think it is," camp but I am curious about your final weight loss with this swap.

Honestly from a fabrication standpoint it doesn't look too bad (I'm one of the ones that suggested laying all this out on the floor in YT and FB like you ended up doing here), and if it ends up significantly less than a tubular K and lightweight strut... setup then I might seriously consider doing it.

Right now my plan is some dropped spindles and I'm going C4 (no HD) brakes already to get something that will handle OK, behave well on the street, look good, brake OK once and still be lighter for straight line performance.
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Old 11-20-2017, 07:58 PM
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Re: I'm putting a C4 front suspension into my trans am!!

Originally Posted by 83 Crossfire TA View Post
We danced around this a little on FB, I'm in the "this isn't going to be handling improvement you think it is," camp but I am curious about your final weight loss with this swap.

Honestly from a fabrication standpoint it doesn't look too bad (I'm one of the ones that suggested laying all this out on the floor in YT and FB like you ended up doing here), and if it ends up significantly less than a tubular K and lightweight strut... setup then I might seriously consider doing it.

Right now my plan is some dropped spindles and I'm going C4 (no HD) brakes already to get something that will handle OK, behave well on the street, look good, brake OK once and still be lighter for straight line performance.
Yep, I do remember our chats lol. As for handling improvements, I'm not really sure what it's going to do considering theres nothing to base this conversion off of, but I can't see it making it any worse. The vette suspension being properly set up and with high end coilovers, better bushings, etc surely shouldn't handle any worse than the factory setup. But my main goal is driver improved feel from the rack and the extra chassis stiffening that this installation entails. In my particular case, I do in fact truly believe it will be a noticeable difference over my old factory-like setup.

But to answer your question, the vette setup came in at roughly 70 lbs give or take less than my old BMR tubular setup, and that included my 670 steering box which is about 8 lbs less than a stock box as well. I left the brakes out when doing the weighing since the same brakes are going back on the new setup so weighing them would be pointless.

I added some weight to the frame rails making them sturdy, but I also dropped all the factory rail metal so who knows how much extra that comes out to be. I can't see there being more than an additional 10-15 lbs in the new frame rails combined.

Other than that, the crossmember has to be cut up a bit to fit the rack, but the overall weight of it shouldn't differ more than 5 or so lbs from what it weighed in stock form. So realistically, I could see a solid 50+ lbs weight savings over even light weight tubular factory style parts. Even less if you drop the sway bar which you technically don't need in a drag setup. And if you built your own crossmember for the vette parts, I'd bet you could save huge weight.

But I'm going more for structural rigidity since mine is a street car, so weight savings wasn't a huge concern. Still a very nice bonus though!
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Old 11-24-2017, 06:02 PM
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Re: I'm putting a C4 front suspension into my trans am!!

Rack is mounted! It was a pain, but I'm glad it's over. Had to level up the crossmember on a bench so the control arm mounting holes were nice and even, get the rack centered perfectly (roughly 85.5mm of the steering bar protruding from the rack body on each side), and then mark the shaft at each end where it should be directly in line with the control arm mounting points. After that was done, I made sure the rack ends were completely level on each side by measuring up from the bench surface, and then measured in from each control arm mount to the racks steering shaft and made sure that was even. After tons of shimmying around and getting it in the perfect spot, the mounts were tacked in place and then finish welded (lower part of the drivers side mount still needs to be made but that'll be cake). I also started to finish up boxing up the crossmember but ran out of day light. Should hopefully have the whole crossmember more or less done by the end of the weekend.
Attached Thumbnails I'm putting a C4 front suspension into my trans am!!-dsc02506.jpg   I'm putting a C4 front suspension into my trans am!!-dsc02507.jpg   I'm putting a C4 front suspension into my trans am!!-dsc02508.jpg  
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Old 11-25-2017, 11:48 AM
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Re: I'm putting a C4 front suspension into my trans am!!

Nice work ! hows the ackerman with that setup ?
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Old 11-25-2017, 06:51 PM
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Re: I'm putting a C4 front suspension into my trans am!!

Originally Posted by 88Greg View Post
Nice work ! hows the ackerman with that setup ?
Ackerman should actually be better than when it was in the vette configuration. By moving the rack slightly rear ward (roughly 3/4") the ackerman angle improves on this setup. I also had to drop the rack down roughly 2" to clear my oil pan, so I'll have to mess with bump steer. I'm assuming and hoping that by dropping the tie rod ends down 2" as well with a bump steer kit, the steering should retain it's correct geometry.
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Old 11-28-2017, 06:49 PM
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Re: I'm putting a C4 front suspension into my trans am!!

Now I'd say it's starting to look like a full suspension

Crossmember is finished except for the front control arm mounts. Only fab left after that is to weld on the coilover mounts once I get them...and that's it. Other than that it's just replacing bushings and freshening everything up. So freaking pumped to finally see the finish line!

Checked out the bump steer quick too. Granted, nothing is aligned properly, but I was getting some slight toe in on compression. With the outer tie rods attached to the spindles in the stock location, that was what I figured because I lowered the rack. A 1.5"-2" bump steer kit should solve that issue, but that'll be stuff I play with towards the end.
Attached Thumbnails I'm putting a C4 front suspension into my trans am!!-dsc02539.jpg   I'm putting a C4 front suspension into my trans am!!-dsc02540.jpg   I'm putting a C4 front suspension into my trans am!!-dsc02536.jpg  
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Old 11-28-2017, 07:45 PM
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Re: I'm putting a C4 front suspension into my trans am!!

That looks excellent.
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Old 11-29-2017, 03:52 PM
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Re: I'm putting a C4 front suspension into my trans am!!

Originally Posted by whitedevilTA View Post
Now I'd say it's starting to look like a full suspension

Crossmember is finished except for the front control arm mounts. Only fab left after that is to weld on the coilover mounts once I get them...and that's it. Other than that it's just replacing bushings and freshening everything up. So freaking pumped to finally see the finish line!

Checked out the bump steer quick too. Granted, nothing is aligned properly, but I was getting some slight toe in on compression. With the outer tie rods attached to the spindles in the stock location, that was what I figured because I lowered the rack. A 1.5"-2" bump steer kit should solve that issue, but that'll be stuff I play with towards the end.
From my understanding usually lowering the rack helps with bump steer, Just get correct the tie rods and it should be better.

Nice to see someone try this, I've always wondered about doing something like this as most rack swaps over the year I've seen on here not workout that well.

For me the only real issues I have with third gen steering is the srub radius with larger wheels and the diminished steering feel due to the inherent nature of the steering box and linkage.

Anyway subscribing.
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Old 12-02-2017, 09:23 PM
  #134  
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Re: I'm putting a C4 front suspension into my trans am!!

Latest vid showing the setup a bit better.


Originally Posted by gp90gta View Post
From my understanding usually lowering the rack helps with bump steer, Just get correct the tie rods and it should be better.

Nice to see someone try this, I've always wondered about doing something like this as most rack swaps over the year I've seen on here not workout that well.

For me the only real issues I have with third gen steering is the srub radius with larger wheels and the diminished steering feel due to the inherent nature of the steering box and linkage.

Anyway subscribing.
Thanks for the sub! I have seen the many attempts at retrofitting a power rack. It just seems like in the end you can't successfully make it work right in a suspension that was engineered for a box. Plus, the factory spindles make it very difficult to get any sort of turning radius out of.

As for scrub radius, it won't be much improved on this setup vs the third gen suspension, but with the rack controlling the steering I think it will help overcome the issue. Or I could just go to an 8" wide wheel vs my current 9" wheels and probably make it almost perfect haha, but I want to see how the car feels and performs when it's done before I think about making changes like that.
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Old 12-05-2017, 06:41 PM
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Re: I'm putting a C4 front suspension into my trans am!!

Started a new job Monday so time working on the car has been very limited, but I did muster up some motivation today to make a mock up "bump steer" tie rod to see how much of the bump steer it got rid of. I cut the tie rod spindle off just below the taper and welded in a 1.5" spacer. This virtually eliminated bump steer movement to the point where I can't notice it anymore with the naked eye. Even with the rim bolted on and looking from directly above the fender, there is no noticeable in/out movement. I'm confident now that with a true bump steer kit I can fine tune it to virtually eliminate any bumpsteer. I'll just have to either get my hands on a bump steer gauge or come up with a home brewed method of precisely checking it.

Also played around with the alignment spacers and shims a bit to see how camber reacted. By eyeballing the wheel from the direct front, it "looks" like with equal size spacers and then 2 additional shims, my camber is probably right around -.5 degrees. Things are looking very good at this point, and I'm confident the car will take to good alignment specs with minimal shimming. Just need those paychecks to start coming in now so I can order some of the good stuff
Attached Thumbnails I'm putting a C4 front suspension into my trans am!!-dsc02542.jpg   I'm putting a C4 front suspension into my trans am!!-dsc02543.jpg   I'm putting a C4 front suspension into my trans am!!-dsc02544.jpg  
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Old 12-26-2017, 08:20 PM
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Re: I'm putting a C4 front suspension into my trans am!!

Progress has been slow with the freezing cold and holiday season, but I managed to get a bit more done. Made both front control arm mounts and have the drivers side welded on. Going to add more gusseting to it but it's in it's place permanently. I honestly can't wait until this crossmember is done. I'm getting extremely sick of cutting and welding lol!
Attached Thumbnails I'm putting a C4 front suspension into my trans am!!-dsc02556.jpg   I'm putting a C4 front suspension into my trans am!!-dsc02557.jpg   I'm putting a C4 front suspension into my trans am!!-dsc02558.jpg  
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Old 12-27-2017, 08:24 AM
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Re: I'm putting a C4 front suspension into my trans am!!

Why are you making your own lower mounts? aren't you using the stock C4 crossmember?
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Old 12-27-2017, 04:54 PM
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Re: I'm putting a C4 front suspension into my trans am!!

Originally Posted by scooter View Post
Why are you making your own lower mounts? aren't you using the stock C4 crossmember?
Yes, I am using the factory C4 crossmember, but the reason for making the front lower mounts is because I had to heavily modify that area in order to drop the steering rack down to clear the oil pan. In doing so, the front control arm mounts were cut off and I had to fabricate new ones. If you look at the pics from the side, the rack will now pass through the squared area behind the control arm mount.
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Old 12-28-2017, 08:24 AM
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Re: I'm putting a C4 front suspension into my trans am!!

Oh ok, I am behind on watching your videos
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Old 01-01-2018, 08:33 PM
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Re: I'm putting a C4 front suspension into my trans am!!

Newest vid! Front control arm mounts are on and I got the drivers side motor mount welded in. Getting so close to finishing this crossmember, and then it's all down hill

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Old 01-13-2018, 05:06 PM
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Re: I'm putting a C4 front suspension into my trans am!!

Extremely productive weekend! Got the welds all cleaned up nicely on the front control arm mounts and primed them. Also got the pass side motor mount welded in. Had to modify it slightly so it would clear my turbo oil drain line, so I cut the front support leg off of it which used to come straight down, and re-welded it on an angle. Should have plenty of room now.
Attached Thumbnails I'm putting a C4 front suspension into my trans am!!-dsc02596.jpg   I'm putting a C4 front suspension into my trans am!!-dsc02598.jpg   I'm putting a C4 front suspension into my trans am!!-dsc02599.jpg  
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Old 01-13-2018, 05:13 PM
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Re: I'm putting a C4 front suspension into my trans am!!

Also started to fab up the rear crossmember braces which are the final piece of the puzzle! They'll tie the crossmember into the rear factory mounting points for the stock crossmember.
Attached Thumbnails I'm putting a C4 front suspension into my trans am!!-dsc02605.jpg   I'm putting a C4 front suspension into my trans am!!-dsc02606.jpg  
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Old 01-15-2018, 04:57 PM
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Re: I'm putting a C4 front suspension into my trans am!!

Crossmember 100% complete! Just have to clean it up a bit, finish prime it, and get a nice coat of paint on. So pumped to be done with this. The crossmember was easily the most time consuming and hardest part of this build. I'm looking very forward to more relaxing straight forward stuff now like replacing bushings and ball joints on the arms.
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Old 01-16-2018, 11:02 PM
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Re: I'm putting a C4 front suspension into my trans am!!

Sweet!
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Old 01-23-2018, 08:04 PM
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Re: I'm putting a C4 front suspension into my trans am!!

New vid showing more progress. Getting so close!

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Old 01-31-2018, 09:38 PM
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Re: I'm putting a C4 front suspension into my trans am!!

Starting to pretty everything up in preparation for the permanent install. Were almost there gents!! Bushing kit will be here tomorrow. Then I just have to paint up the driver's side frame rail and it can all start going together.
Attached Thumbnails I'm putting a C4 front suspension into my trans am!!-dsc02635.jpg   I'm putting a C4 front suspension into my trans am!!-dsc02637.jpg   I'm putting a C4 front suspension into my trans am!!-dsc02642.jpg  
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Old 02-03-2018, 10:31 PM
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Re: I'm putting a C4 front suspension into my trans am!!

Crossmember went in for good today!! Got both frame rails painted and herculined. Bolted in the crossmember with all new stainless hardware, and bolted the engine back to the crossmember so I was able to remove that ugly engine brace. Also hit inside the frame rails with some 3M cavity wax to protect against corrosion. It's finally taking shape!!!
Attached Thumbnails I'm putting a C4 front suspension into my trans am!!-dsc02648.jpg   I'm putting a C4 front suspension into my trans am!!-dsc02652.jpg   I'm putting a C4 front suspension into my trans am!!-dsc02656.jpg  
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Old 02-23-2018, 12:59 PM
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Re: I'm putting a C4 front suspension into my trans am!!

Wow! Been following this for a while. Really great stuff.

I see one problem though............What are you going to do with those ugly strut mount holes?

I suggest getting some skookum mounts and installing them, just to screw with people.
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Old 02-25-2018, 01:06 AM
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Re: I'm putting a C4 front suspension into my trans am!!

Originally Posted by laiky View Post
Wow! Been following this for a while. Really great stuff.

I see one problem though............What are you going to do with those ugly strut mount holes?

I suggest getting some skookum mounts and installing them, just to screw with people.
I plan on making some block off plates from aluminum to cover them up. Probably end up powdercoating them black so they sort of blend in.
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Old 02-25-2018, 01:12 AM
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Re: I'm putting a C4 front suspension into my trans am!!

Received my steering rack and did some modifications to make it work. Had to re-clock the fluid body because in the vette configuration, the fittings point strait up and would have hit my oil pan. Pulled the pins out and rotated it so the fittings face forward instead, and re-drilled the holes for the pins. Had to lengthen the hard lines as well, so I cut them, bent up extensions out of some 1/4" SS line, and used SS sleeves at the connections which I brazed on with silver solder.
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