syc0path

If u check out this post:

https://www.thirdgen.org/forums/tran...vibration.html

u'll see that there are several of us who have a severe rear-end vibration problem. We've done a lot of diagnostic work and thrown a lot of $$ and parts at it, but no1 has come up w/ a solution yet. An emerging theory is that the unibody is experiencing a resonance or harmonic, and it's the unibody itself that's flexing and causing the vibration. If this was the case, then stiffening it w/ subframe connectors could be the answer.

So, is there any1 who has subframe connectors but also has a similar rear-end vibration problem? Or better yet, is there any1 who had the rear-end vibe problem and it went away after u installed the subframe connectors?

scorchmaster

iTrader: (6)

I used to have a horrible rear end vibration. When I still had a manual, no matter how slow or fast I slipped the clutch, the rear end would bounce up and down like mad like I was wheel hopping. When I was cruising going 70 it would start again. It turned out my panhard bar was bent, it took me a while to notice that because I never paid attention to it. I replaced it with a hotchkis one and the problem was gone.

Regardless, subframe connectors were the best thing I've ever done to my car. My spohn crossmember has a front driveshaft loop which used to pound against my floorboard when I was cruising down the highway. I got some spohn subframes installed the problem was gone and the chassis felt absolutely amazing, much stiffer than before. So it cant hurt with sfc's, I'd get them anyways. As for the rear end shake, check your panhard bar to see if it's straight. Otherwise, as that post says, check to see your driveshaft is balanced and at the right pinion angle, that could vibrate your car too.

Guest

I seriously doubt it. GM made 3 versions of the body, not to mention numerous aftermarket jobs... and none of those I know of have any problems. Unless you have some serious body cracks from fatigue, I'd be looking elsewhere. I noticed nobody, or so it seems, has checked the rear alignment. Mustangs have a problem with damaging/destroying the 'torque boxes' where the rear LCA's mount. Our cars are built much better there, but cant hurt to look and check that, the bushings (if you already havent) and the alignment. I'd also be looking for wear patterns in the tires, sounds like almost all these cars its not a front end vibration so its probably in the back if the drivetrain is ok.

a1990camarors

defiently check your panhard bar my stock one was mangled they dont hold up too much change ur lca bushings make sure the rear is aligned etc. Also the driveshaft might be out of balance start wit the simple stuff thou.

syc0path

I (along w/ several other people in that post) have already done all of these things except for the rear alignment. But I can put the car on jackstands and run it up to 70mph and the vibration is still there. If it was an alignment issue, u wouldn't feel a vibe w/ the tires off the ground. I've also put over 40k miles on the car since this started happening and I've never had a problem w/ funny tire wear.

scorchmaster

iTrader: (6)

I remember seeing one case, and it seems a bit extreme, but the axle inside the tube was bent. The axle when it was rotating was actually deflecting the axle tubes causing them to move up and down. I wish I could find it, but he had the same phantom vibration problem too. Maybe your axles got slightly bent, that would cause some nasty vibrations which would only get worse, or maybe only noticed at higher mphs. It's really easy to pull an axle out, see if yours are still straight.

Guest

For that matter, a car wont resonate sitting on stands either.

syc0path

Yeah it could, becuz the unibody is connected to both the motor/trans and the rear axle assembly. If it's not holding both of those things stiff relative to each other, that could cause a vibe.

Guest

But you've isolated the body through the jackstands. Thats going to kill the resonance effect you had before. Resonance works on structure, if you alter the structure (even stands at the LCA), you've surely altered it enough to ruin the harmonic frequency of the car sitting on tires.

Bandit5

I had this problem a few years back... it went away after a transmission rebuild.

I think the problem (or at least mine) was caused by an improper pinion angle. Try messing with that and see if it helps. It is going to take different angles for different setups, but I am sure someone here will be smart enough to figure it out.

Orr89RocZ

iTrader: (20)

not a bent rim/axle/unbalanced wheel/bad tires?

Guest

They've tried all the basic stuff, from what I saw in the other post. Driveshafts, wheels, tires, checked axles, springs, shocks, etc.

If its doing it on the road at speed and stationary on jackstands, its not going to be resonance. Its something in the drivetrain. I'm not sure its age or abuse either, I have a car that has 170k on it and its been bent and abused and its totally fine at 140.

a1990camarors

its def a drivetrain issue ur unibody isnt causing this unless its severly screwed. make sure u know where the vibration is too ive heard off people driving down the road feeling a vibration and assuming where its coming from the rear etc and it ends up bieng front ball joints lmao. check tranny mount everything. other possibilites you could go too a junk yard get another rear end get a driveshaft bolt it up see if that does anything its basically a process of elimination dont go chasing retarded stuff like frame alignment thou. stick too the drivetrain tranny back.

???

iTrader: (5)

its the drive shaft... don't mess with trying to balance one. it doesn't work.


go to a junk yard, find a stock older auto car since they were slow and never seem to hurt the shaft. find one that still have the factory installed metal cross clip thing that holds the two loose rear u-joints cups on when building them on the line. if you find a good one, both sides will still be intact and holding the cups on.

put that in your car and it will stop your vib... i also chased this for like 10years, untill i happen to pick on a new stock shaft for free and it all went away. i had 2 built and that never worked. only bad that is the stock ones only last for about 6 months before they slowly start to vib again. but i ended up finding a alum one from a ls1 car and that one has seemed to last for a few years.

syc0path

Yeah, I see what u'r saying. But it is still possible, though not likely. Imagine if the torsion bars were loose where they mount to the body. That would allow the axle assembly to move back and forth as the rear wheels spin, and that would cause a vibration whether the car was in the air or not. Now imagine if, instead of the torsion bars being loose, that the force of the rear axle moving back and forth was causing a resonance in the unibody. As the unibody flexes it would allow the mounting pt to move. That would have the same effect as if the torsion bars were loose, and it would happen even if the car was off the ground. It wouldn't be exactly the same, but it wouldn't go away either. And in fact, it did change somewhat -- the vibe started at a lower speed. And raising the jack up and down would interrupt the resonance -- just like it did when I tested it.

I know it's not a very likely scenario, but I've already checked, double-checked, and in most cases, triple-checked all the likely stuff. So now I'm trying to do some research to eliminate this as an unlikely, but still possible, scenario before I go invest more time, $$, and effort to test it.

All of the other suggestions since my last post have already been done, except the trans rebuild. But I did replace the tailshaft bushing and it was in great shape. And I can shift the car in neutral and the vibe remains, so I don't think it's deeper in the trans either.

Bandit5

I also did have a custom steel drive shaft made for the car... but I am not sure if the vibration was still there with it. It wasn't that much money though, plus I needed one.

cajunnola

I dirt track we bend axles quite often. We usually bend them bad enough that it is easy to tell but it is very difficult to tell one is bent if it isn't drastic. You could probably pull them and put them on a lathe. If ours aren't really bad we don't care. we just run them. But that won't work for your street car. So I would check those out. They bend easier than you would think.

syc0path

I put in a complete rear axle assembly and it made absolutely no difference whatsoever.

Guys, if u read the other post, u'll see that we've already tried all of this stuff. That's why I'm asking about the SC's.

Guest

Unless you're tight on money, put some on. It will only help the structure of the car. I think the Spohn and UMI and maybe BMR's use the front LCA bolt and are welded there.

rhuarc31

Without actually hearing the noise dunno if this will help or not. I chased a similar problem for a while on two different cars, drove me nuts. Did all the stuff you talked about, rebushed everything I could think of. When adding the the LCA's and subframe connectors made it worse I was sure SOMETHING was screwed in the rear end. On one car I was right, turned out to be a bad differential bearing. On the other I thought the same thing and replaced those, still did it, I started pulling my hair out. That is until I had to drop the tank and put a new fuel pump in. when I put everything back up I changed the angle of the exhaust outlets and the problem went away, turned out to be some funky exhaust resonance/reflection thing.

syc0path

Yeah I know the kinda vibration u'r talking about, but that's not the problem I'm having. I can shut the engine off and coast at freeway speeds and the vibe is still there. It's also speed related, not RPM related.

jstoltz

iTrader: (16)

did you check the trans yoke to make sure there is no slop? U joints? make a video and put it on here. is there any noise from the vibration at all or just the normal out of balance sound from driving?

syc0path

I've done all that. The video is a good idea, but unfortunately the weather is starting to get nasty and I think I'm done driving her for the yr. I just took the insurance off yesterday.

There's no grinding or grating noises if that's what u'r asking. There's a "wump-wump-wump" noise that corresponds to the vibration, but that's just the normal out of balance sound u mentioned.

antman89iroc

I have a vibration that feels like a rear tire out of balance. Not a high frequency buzz but a low wobble. It has persisted through different rear ends, gear ratios, wheels, tires ect. It happens at around 65 MPH. I had it before sub frame connectors and after. So sub frame connectors didn't help in my case. I thought the previous comments about the rear suspension "torque boxes" was interesting. I have noticed that some of the body seam glue has fallen out in places like the front frame area under the wheel house. I wonder if the whole unibody is giving way. But in regard to the sub frame connectors- the whole care seems more solid after installing them. I do notice more vibration in general after adding them.

syc0path

Thank u antman... that's exactly the type of info I'm looking for! Unfortunately it's not the answer I wanted to hear, but it's good to know. Thanx again...