I drive a 92 camaro RS with a 305. I've had a vibration for about 3 years now I've been trying to fix. Details: at about 70mph the vibration starts, as i accelerate more the vibration is worse. At about 80mph the whole car is shaking so no it's not in the seat or in the steering wheel, it's everything. Here's what I've done to try to fix it so far.Brand new rims and tires( yes they've been balanced and aligned plenty of times and the vibration was there even with the old rims and tires). Brand new aluminum driveshaft, brand new shocks and struts, entire front end suspension-center link, idler arm, inner and outer tie rods and adjustment sleeves, both lower ball joints, both sway bar end links, polyurethane torque arm bushing, brand new rotors, calipers, break pads, and inner and outer wheel bearings all on both sides. then just for kicks...just changed the spark plugs.....please help.

If you feel it through your seat bottom, it's probably in the rear axle or driveshaft. Is the vibration steady, or does it cycle stronger/milder like a heartbeat?
David

it's steady

has the car been involved in an accident? How does the rear track with the front?

it looks like it might be a little off. one of my friends suggested that too. when i got the frame checked in the very beginning they said it was right at specs. they did say that it looked like it had been hit from the rear drivers side

would that only have the vibrations at higher speeds tho? or would it be consistant

Ive seen a few that the rear was cocked at the wrong angle. Up or down(pinion angle) AND left to right(entire axle)....

If the vibs increase with speed then its obvious its something mechanical that increases with speed, right?

If its constant, then speed has nothing to do with it. Thus, alignment of the joints in the rear....

so how do i go about getting that looked at? home come i dont feel anything at say 60 or 65? also, how much does something like that cost? this may also sound like a dumb question, but i don't have the plastic gaurd on the inside of my wheel wells on the front, is there any way maybe air getting in the ground effects or something that could cause it at all

Drive shaft dropped a balance tag.
Drum or disc out of balance....
The latter find a shop that does wheel balance on the car...this checks everything on the stub axle

Are the rims multi slot...
If so use std tapper lug nutts to center the rims, tightening just nicked up, then remove one at a time replacing with the correct lug nutstightened so rim doesnt move.

I dont know if the 92 has disks or rear drums, but check it one of the blance tags has been filed a bit to let the rim sit flush....or visa versa, the rim sits margunallt on a tag
paint between rim and hub can also cause strange stuff at higer mph

Could it be bad or loose motor mount issue?

motor mounts are good. the rear breaks are drum. i dont really know what some of that means but i'll tear it apart and look for some abnormalities. when it comes to most of that though. even with the stock rims on it vibrated the same way before the new rims came

Can you only feel it, or can you hear it too?

If you can hear it, a bad bearing in the rear end will create a vibration and also make a lot of noise that gets louder as you go faster.

A bent axle can cause vibration without making much noise.

Just cause I didn't see it mentioned anywhere. Three items come to mind. First is Harmonic balancer out of whack or second, the HB can't make up for an inbalanced rotating system in the motor. Lastly I didn't see your tranny type mentioned, but an out of balance flywheel/flexplate will give you big issues at higher RPM's. You can check the flywheel/flexplate by rotating it by hand underneath and looking to see if a weight has been dislodged, if that's the case then it will have to be pulled and reballance or replaced.
The HB would have to be pulled and a new one installed to go that route. The innards of the motor is another ball game as it would have to be dissassembled and each part weighed then ground down to match the other like parts. Granted this issue is more for when your going high RPM's (up into the 7-9k range) where the engine will come apart.

It sounds to me like it is speed related, but just to make sure it is speed (MPH) related and not engine speed related.
Get up to the speed where it vibrates, put the car in neutral and see if the vibration stops.

If not that means that no part of the engine or anything bolted to it is causing the vibration.

It sounds like you have checked everything that quickly comes to mind for a speed related vibration. There are two ideas I would look into that were mentioned already but they seem like the most likely two.

1. Check your pinion angle, I have heard a lot of complaints recently about vibes caused by pinion angle problems.

2. Drums or discs out of balance. My money would be on the rear drums. Often there are large weights that look like they are just barely attached to the outside of the drum.

Yeah, nobody said pinion angle. Here's some help with it. http://www.iedls.com/measure.html

Ive seen a few that the rear was cocked at the wrong angle. Up or down(pinion angle) AND left to right(entire axle)....
:boring:

Have you tried running it on jackstands under the axle to isolate the front and rear? With no tire to road contact this would also eliminate out of round tire/wheel as a factor. If you don't feel the vibration in neutral at the rpm where you are having problems is from the tailshaft back. Did you check your u-joints?

thx. i'm takin it in on friday. i'll get those checked for sure. running the car at 80mph on jack stands sounds a little risky to me. havent checked the u-joints, somebody told me that it would be a constant problem...not just at high speeds