So I have this 1989 Coupe Quattro that has an isse with it's drivetrain.

Every time I let of the gas pedal completely the whole car kind of jumps or vibrates heavily. The same happends when I press the pedal again. It's usually worse when releasing. It almost feels like the whole drivetrain is falling apart.

Upon inspection my engine mounts are in good shape and my rear differential mounts look new(polyurethane). Haven't inspected the gearbox, but I would assume it's the same.

I really have no clue on where to start looking other than my gearbox mounts. If they look good, where to start? CV joints? Broken rear diff?

Any suggestions would be greatly appreciated.

 

Can you feel it in the steering wheel? Especially if you are turning the wheel to one side or the other. The CV Joints would be the first place I'd look. There are also some transmission mounts at the rear of the subframe you might inspect too. However, I'd lean towards the CV joints being the issue here.

 

The steering wheels feels fine. There's some vibrations but they're not related to the issue I'm having. The entire car just jumps or jerks every time I release or press the throttle.

Feels almost like the CV joints on the transaxle to my rear diff has some issues.

 

Could be the rear CV joints like you said. They are made the same as the fronts and will wear out. A trick to get more life out of them is, if both sides are the same, switch them out from side to side and let them run the other way since 99% of the time they are rotating forward. They may pop in reverse from time to time though.

 

I have some friends did exactly that on some Porsche 944's.

I might test that out. Doesn't cost anything. Unless I strip some of the bolts, which is highly likely on an old car like this.

 

That's what I do on my 944 too.. LOL Just make sure you clean out the head of the bolt and peck the 12-point tool down into the socket with a small hammer to make sure it's all the way in and you shouldn't have any issues. I've not rounded one out yet. At least you can get to them with some vice grips if you do.