Ok, well those posts in that thread talk about a bad torque converter. But if I'm going down the freeway, I can shift the car into neutral and shut the engine off and the vibration doesn't change. I know shutting the engine off will stop the outer portion of the TC from rotating (since it's bolted to the flywheel), and I assume shifting into neutral will stop the fan inside from rotating. Can any1 confirm that?

 

Any more ideas?? Or does any1 see any problems in my testing methods?

 

Ok, I have yet another idea... I was watching Trucks on Spike this weekend and they showed a really ez method to make sure the driveshaft angle at the trans matches the angle at the axle. They took a straight piece of stiff wire, lined it up w/ the body of the trans, and bent part of the wire till it matched the center of the driveshaft. Then they took the wire, lined up 1 end w/ the driveshaft, and lined up the other w/ the differential. Those 2 angles should be the same (as discussed earlier in this thread) and this seems like a really ez way to verify that. So hopefully I'll get some time this week to pull her out and try it.

I took my g/f out on the town Sat night... it was a beautiful day and it was perfect for cruising w/ the T-tops out and the foglights on. Then we drove home on the freeway and the vibe seemed like it was worse than ever

 

I have a similar problem, at least when I still had the car together. Mine did it at 75+ and most noticeable when I was off the gas. Seems the 4th Gen guys have the same problem. I was just over at LS1 Tech and see the same comments.

http://ls1tech.com/forums/showthread...bration&page=3

 

I've only glanced through the postings however I didn't see any mention of the differential itself.
Worn pinions and increased backlash are common causes of vibratrions or low frequency 'humming' particularly using the tests you've described.

 

I swapped in a complete rear axle assembly... didn't have any effect.

 

Well I put the car up on blocks and tried to measure... but of course everything looks ezr on TV -- especially since they were doing it on a partially assembled 4x4 instead of a completed assemble sports car! But if it is off, it isn't off by much... it looked the same as far as I can tell w/ the wire. Just by eyeballing it, it looks like there's just a little more of an angle from the trans to the DS than from the DS to the rear axle, but it's hard to judge that just by looking. How much of a difference in angle would it take to create that strong of a vibration?

Another thing I didn't think about is that I should have raised and lowered the rear axle -- the angles should be the same thru the travel -- becuz a more severe angle might have been ezr to measure. And I would have had more room inside the tunnel to look at the wire compared to the DS.

 

I took my neighbor (who has had several 2nd gen Firebirds) for a ride a few days ago. He thinks that the tires are flatspotted, which is causing a low-speed vibration. That could be, but it also could be that the tires are squared off cuz the car sits so much. The tires are also old and have very little tread on them.

Then we went for a ride on the freeway and he pointed out that the driver's side of the hood vibrates a lot more than the pass side of the hood. There's also a minor side-to-side wobble in the steering wheel. So he tried to tell me that something in the front of the car is causing the whole vibration problem. Well we did have a problem w/ the caliper bolt hole on the driver's spindle getting stripped out, and we replaced it w/ a used part. So I thought that might be suspect. But it could also just be the tires... so what I did was swap the front tires from side to side. And guess what? Neither side of the hood vibrated very much and the wobble in the steering wheel was almost gone. If it was the spindle, the hood vibration would have stayed on the driver's side. If it was a rim, the hood vibration would have changed sides. But since it went away, the only explanation that makes sense is that it was a problem w/ the tire tread -- and running the tires backwards minimized the impact becuz they're not worn in in that direction.

I know it's not a problem in the front end, becuz the same vibration is present even when the car is on jackstands. But this is the 2nd time I've had some1 in the car who gets confused by the minor vibrations caused by the old tires and can't concentrate on the real vibration. So unfortunately, I think it's time to step up and spend a few hundred $$ on some tires for a car that's lucky to see 200 miles/yr While the tires are off, it will also give me the opportunity to make sure the rims themselves are causing any minor vibes. I don't want anything distracting "experts" from the actual vibration. It will also help me determine if I've made any improvements from stuff I've done or will do.

 

I got her our again this weekend and took another shot at measuring the driveline angles -- this time w/ the rear axle all the way down. I also figured out a lot ezr way to measure. It's kinda hard to explain w/o a pic, but the driveshaft is basically an aluminum tube w/ a bracket welded to each end that holds the U-joints. As long as the distance from the weld to the center of the needle bearing caps on the bearings that are closest to the DS are the same (and they are), and the length of the bearings across the diameter of the DS are the same (and they are), then the minimum distance between the center of the needle bearing cap to the weld for the bracket should also be same. If they're not, then the only thing left that could explain the difference would be that the angle from the trans to the DS was different than the angle from the DS to the axle.

In my case however, those distances were identical. And that means the angles are identical and that is not the cause of the vibration.

 

Syco, I hate to sound like a broken record but I have done all the things that you said that you are trying and doing. I even installed an entire rearend but when I changed my torque converter to a non-lockup "ALL" the vibs went away. My car is as smooth as silck. Someone has to try a torque converter !!

Auggie

 

Yeah u'r right... especially given my new theory that there are multiple causes for the vibration in my car.

So, where do I get a non-lockup torque converter? Is it the lockup mechanism itself that goes bad and causes the vibe? I mean, it's not as simple as just disconnecting the wiring so it doesn't lock up, right?

 

Well its been a few years but all I did was buy a rebuilt torque converter for $150 I think from NAPA (I don't remember what it was used on) an then called Art Carr Tranmissions and ordered a kit to reroute the oil. You might want to go to there web site or call them for the info.

Auggie

 

Guys, listen to Auggie about the torque convertor suggestion. Also, check out my thread that he mentions in one of his posts above. A new TC solved my vibration issue.

 

Check out my post under vibration.
I can only comment on my combination ( 700R4 with lockup convertor ) but it seems it's not the torque convertor itself ( I experimented with 3 convertors and 3 different 700's ) but the relationship between the convertor and flexplate. There's even a test procedure in the GM manual called 'Flywheel Assembly/Torque Convertor Clutch Vibration Test'. Decouple the convertor , rotate it 120 degrees and reconnect. Repeat if necessary.
After my latest install, I seem to have hit upon the best relationship between the two. I guess that even though both components are balanced individually, there is a stack up of tolerances that results in a slightly unbalanced condition with a resulting vibration.
Wouldn't have believed it if it didn't happen to me. And I've been at this for YEARS!

 

have an '86 T/A with a 350 backed with a t-5. everyday driving there are no vibrations and up to 65-70 everything is fine too. at 75+ it vibrates the majority of the interior or whole body, however you want to look at it. the dash vibrates pretty bad too. has 4.11s in it. only other suspension thing i've changed is to put relocation brackets on it and have also recently replaced the front struts. has had this problem with three sets of tires. if i let off and put it in neutral at 75+ it still vibrates so i dont think its a motor issue. everyone else seems to have similar problems but i didnt want to just start replacing everything left and right and not get anywhere with the problem. is there one thing anyone would recommend that i try to replace first? thanks !

 

My '83 had a nasty highway vibe. It started at about 2250, then got steadily worse, REALLY bad at about 2400, then practically gone at 2600. T-5 trans 2.73 open rear. Not sure about an exact speed but figure it was between 65-75mph judging by timing milemarkers (speedo doesn't work).

I fixed this by installing a pilot bushing cuz my mechanic didn't. Whoops. Anyway, if your vibe isn't TERRIBLE and you have a stick, that's one possibility.

I know a couple of guys who worked on vibe problems in this thread did replace torque arms, but if you have a bent one, it'll hold your rear axle at a bad angle. Just a thought.

 

I've got a vibration also with my Iroc. My vibe is RPM specific, 1600-1800 RPM. It doesn't do it in park or neutral, only under load. And get this, it does it only when I bear to the left. It's fine while going straight or bearing to the right. I took the car to the shop last week and they drove the car and put it up on the lift and said it could possibly be my D.S. needs to be balanced. I should also note, that before I took the car to the shop it would vibrate at the above mentioned RPM under initial acceleration and at highway speed, however, if I went right or left the vibes went away. I've had the transmission mount replaced (stock rubber) and the vibes went away for a week. A co-worker of mine suggested sagging motor mounts. The vibe has progressively gotten better with the tranny mount being replaced and having the guys at the shop looking at it( and they didn't do anything to it). I've got Mastercraft tires(225/60hr15), Edelbrock TES headers and a Flowmaster American Thunder cat-back on the car and the vibe sounds like exhaust components rubbing against the k-frame. I feel it in the tranny tunnel, seat, and steering wheel(slightly). I'm wondering if it's suspension, mounts, rear-end, tires, wheel bearings or exhaust. Any suggestions are welcome and appreciated. Sorry for the long post, but I didn't want to leave any info out.

 

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My 88 IROC with a 305 5speed has a vibration at 3500 to 4000 rpms, then it goes away. Dosent matter the speed its only when I hit those certain rpms. I had an EC trans mount and changed it to a stock rubber one, no improvement.

I have run the car while parked and just slowly brought the rpms up to 3500 and it seems the vibration is there, Can it be from the muffler which is a chambered Hooker system?

My axles also seem to have some excesive end play.

I think this tread should be kept going

Mike

 

Driveshaft, wheels, tires, rear end, and suspension will cause speed related vibrations. Since you said that you can hear the exhaust hitting something I would change both motor mounts and check the whole exhaust system for proper clearance. It should be at least 1/2" away from anything.

Rob

 

The driver side header flange looks like it's maybe an 1/8 to 1/4 inch away from the k-frame. I was thiking motor mounts as well, but when put the car in gear with my foot on the break and give it a little gas, the motor doesn't **** up to one side like I thought a bad mount would do. My driver side front wheel bearing is loose and has alot of freeplay in it(the left frt wheel hops if I make hard left turns)

 

there is a tool to measure what order the vibration is. It is called an eva or eva 2 or there might even be newer versions. I took a class on vibrations when I worked for a large car manufacturer and this tool is used with a computer program and arranges vibrations of the vehicle in an order. It is a very efficient vibration finding tool and might be your only alternative to find someone in your area that knows how to use it. It uses a magnetic base that can be attached and reads out numbers. These numbers are used by the computer program to isolate if it is an engine vibration, driveline vibration, based on the resonance and "order" how it vibrates. It will find bad tires, anything that you could possibly think of. I used it with success to find a body bushing that was defective under the left front of a chevy tahoe one time, and did multiple tests with weights on a driveline with an instructor to balance a driveline while installed in a vehicle!!! All vibrations in a vehicle fall into a category-order and will save you loads of cash when used properly. Hope this helps.

 

I was getting all set to do this, but I just thought of something... if u shut the engine off, that stops the outside of the torque converter from rotating (becuz it's bolted to the flywheel). When I shut the engine off and shift into neutral while cruising down the freeway, the vibration continues. So unbolting the converter from the flywheel and rotating it 120 degrees won't help me... right?

 

That would be correct. If your shut the engine off then the torque converter is not spinning.

 

Well the outside of the torque converter isn't spinning, but what about the fan inside?

I got new tires a couple weeks ago and finally got a chance to take my car out for a long ride on the freeway. The vibration is definitely much better, presumably becuz the old tires were out-of-round/flat-spotted/dried out/old. W/ that part of the vibration gone, it's ezr to feel the underlying vibration that I can't figure out.

Anyway, I shut the car down and shifted into neutral as a I was getting off the freeway, but the vibration continued and didn't seem to be affected at all. So I can rule out the outside of the torque converter at least... of course, if it was the outside of the torque converter, it would be RPM related, not speed related. And the problem is not RPM related.

And I don't think the fan inside the TC is the problem either... if the engine is off, the outside of the TC is stationary. And if the trans is in neutral, there isn't much force from the trans to turn the fan. So when the outside stops, the viscosity of the oil inside the TC would put a lot of drag on the fan and, at the very least, slow it down drastically. But the vibration was unaffected.

That, and the fact that the vibration is not RPM related, tells me that it's not the TC.

 

I went through this vibration issue for a few years until I finally got it solved. My car is so much more fun to drive now that I know it's not going to vibrate itself apart. Here's a seriously long thread with all the symptoms and troubleshooting I did until I finally figured it out:

https://www.thirdgen.org/forums/tran...-has-me-4.html

 

So... u went to an aluminum driveshaft? I already have an aluminum DS from a 4th gen and it didn't make any difference.

 

This was recently posted on the Chassis & Suspension board:

https://www.thirdgen.org/forums/susp...ue-solved.html

Broken bolts for the torque arm to the rear differential mounting.

RBob.

 

I installed a complete rear axle assembly including the torque arms and it didn't make any difference.

 

I was kinda watching the "PowerBlock" on Spike this past weekend... I had it on in the background and wasn't paying close attention, but I think it was "HorsePower TV". I think they had a '90s-era Thunderbird and they said something about the unibody sagging over time. They showed a preview that involved jacking the car up and welding in some plates to straighten and stiffen it. Any1 know what I'm talking about? Could these be a potential explanation for the vibration problems many of us have been experiencing?

 

frame might be bent?

 

Thought about that... but the car has never been in an accident, so I don't know how the frame could have been bent.

 

off the top of my head. bad U-joints, rear or front rims need balanced, bad shocks, the tires themselves are bad (tough to tell on this, you need to take them in and have them dismounted) hell, a bad tie rod end might do it too. I'm not trying to call you a liar, but if you aren't the original owner..you never know if its been wrecked and fixed before. my car was stolen and totaled..once I'm done with it, nobody will ever be able to tell it happened.

 

Well, you can add mine to the list 87 iroc - pretty much EVERYTHING rebuilt
Vibration ongoing for 3 years now
tires - replaced with new - same
wheels - balanced 3 times
brakes - new hardware all 4 corners
engine - 350TPI - completely new engine
tranny, 700-r4 - rebuilt
3 driveshafts - u-joints, yokes, balanced, the works
totally different 9 bolt rear (89 1le rear end)
tranny mount is stock rubber
no urethane anywhere
vibrates at 55+ shakes dash, steering wheel, shifter, seats, body, etc
has SFC's.
If you are going along at say 60, and you go downhill, and you put tranny in neutral, vibration still occurs, doesn't change.
suspension has been checked 3 times
We have NOT done the pinion thing yet, apparently you can't shim these, you need an adjustable arm.
I've thrown at least $2k in this thing just trying to fix the vibration. If we do the pinion and it DOESNT fix it, i'm out of ideas, options and money! Anything i missed, someone please let me know.

 

does the car have brake drums ,,, you may have lost a weight off one of the drums...

 

nope - 4 wheel disc all around. ls1 up front and 1le in back. also changed BOTH axels in rear and wheel bearings on all 4 corners (both inner and outer races in front)

 

I had a nasty vibration too. Changed tires/ rims. Motor, trans, front struts, front spindles and all mounts in drive line. I changed out my rear lower control arms and pan hard rod and it finally went away. I had planned on those parts so I was a little stoked by the side effect. I had a bent pan hard rod. Hope my experience helps someone cause it was by far the cheapest thing I've done. Founder performance; I thank u

 

what about the panhard bar was making it vibrate? and what specific tests did Founder performance run to find this?

 

Im adding myself to the list
Had 0 vibrations untill i swapped in a used th400, and converter, new x member, new trans mount, and new chromolly drive shaft

May the fun begin

 

For those of you getting vibrations, here's what you should check first. See if your wheels are bent, make sure your tires are balanced, check your alignment, check for any bent or broken suspension parts, see if your axle is bent, see if your driveshaft is bent, check your u-joints, check your pinion for play, check your differential and axles for play, look for broken C-clips, check your wheel bearings.

 

i found my bar to have a bend in it that made more pressure on the left side. i changed the parts cause i wanted to. i had an awful vibration just like the rest. it would start at 70 then get worse til 105. unbearable by that point. i was just happy as a pig in **** to get rid of that damn vibration. noticed it on my way home from my job that day.

 

For those with the rpm related vibration, has anyone thought of the tailshaft mounted exhaust hanger? I have a vibration that comes and goes every few hundred rpm and its the long stretch of exhaust that is unsupported since I don't have the center hanger.