I am ready to pull my hair out of my skull.

I have a 1987 Trans Am GTA 305 that I bought two months ago. I bought it from the original owner, the car had 52,426 miles when I took it home. It's in fantastic shape, except for the fact that it vibrates around 70mph+. Now, before everyone starts throwing the typical responses at me, here is what I have had done, in order:

Replaced tires
full 4-wheel alignment
Wheels balanced (twice)
idler arm replacement
driveshaft balanced
driveshaft replaced (with aluminum)
old driveshaft rebalanced, re-installed
rear-end completely disassembled, then reassembled and reinstalled
new front brakes
new rear brakes

And is still vibrates. It's enough to be noticeable and annoy me when I have such a nice example of a thirdgen otherwise. it does become a bit less noticeable the faster I go (over 80mph).

All front and rear suspension components are in good shape. Motor mounts, transmission mounts, and u-joints have been looked at and test fine. Everything in the driveshaft-rearend is within tolerance range, but when they put it up in the rack they (my mechanic) can see it wobble. I have run out of funds this year to throw at the damn thing and I don't even know what else to attempt. The _only_ other problem the car has is that the rear brakes seem to be out of adjustment somewhat-the driver's rear locks up too easy with hard stopping.

I'm on the verge of putting the thing back up for sale and washing my hands of it. Car's never been wrecked, either. Where do i look next?

 

What is it that the mechanic sees wobble on the rack?

I'm almost ready to guess you have a bent axle in the rear. Support the rear end on jackstands, start the engine, put it in drive and bring the spedo up to about 40mph and have a look at both rear wheels.

 

Good call on that one. I'll bet 99% of issues people have with the vibration problems on these cars are bent axles.

All it takes is one good wack into a curb to bend em. It's usually real easy to see. Just take your wheel and the drum off and get the axle spinning and you can see the wobble. Axles are easy to replace but aren't cheap. And you're rolling the dice getting junk yard ones. I have two complete rears in the garage and they have a total of 4 bent axles in them. Seems Camaro owners enjoy slamming into to curves for some reason.

 

I have a set of 26 spline axles if yours are bent . Cover the shipping and they are yours . I upgraded to 28s . Dont give up G/L

 

thanks for the advice guys....it will be a while before i can have it looked at again (winter weather/holiday shopping) but i'm going to keep all of this in mind when I dig back in in the spring.