88 S4, S5 engine, stock everything else.

Alright guys. I am so fed up with this car right now, and I'm desperate for a solution. Here's back story:

I recently removed the sub frame to swap out the upper control arm bushings (the ones with the adjustment bolts). After replacing everything. I took the car for a test drive. I began to feel a minor vibration from the rear end at about 40mph. Then it got worse and worse, and I went back home. Upon inspection of the rear end, I see that my lug nuts are all loose, and I did in fact torque them down before leaving. I ditched the crappy tuner lugs, and got some wider, acorn style lugs. At this point the rear end is jacked up with the wheels spinning free, because I will not drive it like this. The new lugs did not solve my problem. Here is what I have done and where I am at now.

Note: It is NOT the wheels or tires. I took the rims to NTB and had my dad check the round and balance. Both are perfect.

The vibration is a constant thumpthumpthump, very fast, and it vibrates the car in time with the noise.

Both tires on, accelerate to 100 mph. (Vibration begins ~45mph, continues from there)
One or the other tire off, same test. (Vibration the same)
Both tires off, same test. (No vibration)
Brake pads removed, both tires on, same test. (Vibration the same)
Re-aligned the drive shaft every way it can be bolted on. (Vibration the same)

The drive shaft doesn't seem to have any play in it, but the driver's side stub shaft does have a medium amount of play to it. However the vibration seems to come more from the passenger's side. I can turn the drive shaft maybe a half inch to an inch before the wheels begin to turn.

I did not mark the locations of either the half shafts or the drive shaft for re installation. I have never had a problem with it before, until now maybe?

When I let the wheels spin down to a stop, a loud metallic clang is heard. Hard to describe but whatever...

The wheels look to have a bit of wobble, but it may be a trick of the light.


Huge thanks to anyone that can point me in the right direction!!!


** edit

I just had a thought. The cheap *** tuner lugs i had on the rims v-ed out the holes on the rims (Mustang GT rims) I thought the acorn lugs would correct this. Now, the tire balanced out fine at the shop, but if you know anything about a balancer, you know that they dont bolt the rim to it. There is a cone shaped metal piece that slides into the center hole. The rims do have a slight up and down motion to them in motion.
Any thoughts on this?

 

fast way..
put your wheels on the back and the vibrations should continue if its a driveline issue. if its a rim issue then it would stop.

maybe when you took the half shafts out you switched them up.. or you didnt bolt somethign down all the way or something like rust or gunk is wedged inbetween the stubs and the shaft..

i would check that my axle bolts torqued to spec(doesnt hurt to double check)
unless your certain that you didnt swap the half shafts around i would try that (the only reason i even mention this is because stuff wears in a certain way and since the half shafts are balanced maybe one weighed more then the other causing a different sort of wear. its plausible.)

but before you go thru all that effort i would try and find a 5x114.3 rims that you can borrow and try it because you can bend a rim where it rolls straight as an arrow but the hub is bent.

 

I'm not sure what you mean by this.


I did not mark the halfshafts when un/re installing them. I had no idea that it was that important. Problem now is that they are most likely both in the wrong place, and it's gonna be hard to find the right combination... but it's better than tearing the whole thing back out. How sure are you that having both half axles being out of balance would do it? I had no idea they were even balanced.

 

sorry im a idiot for the way i answered your post.

what i ment to say was rotate your tires put your front wheels in the back and the back wheels in the front. take it out for a spin and see if you get the vibrations again *remember if you feel the steering wheel shaking or vibrating the problems in the front. if you feel the vibrations in your ***(not being a smart ***) its a problem coming from the rear.

do this and see what happens if you have a budddy with wheels that fit you can try throwing them on the rear and avoid rotating your tires.

when ever you take a drive shaft out if its balanced to that side or not you should put a line going from the flange of the axle to the flange of the stubs like this,

Thats not the best picture but you get the idea . the reason for this is because **** wears different you see what im saying,

but before you assume that the axles are the culprit change your tires around or borrow tires and see what happens. if the problems continue you are going to have to get under and look to see if maybe you can match up rust or something that shows you how the axle was in place.
i hope this is clear
godspeed

 

Whenever the suspension is modified like that, the alignment will now be not good.
Have that checked out next since you said you checked everything else.

 

How the hell do you check rear alignment. Everyone keeps telling me that but I searched and find nothing. I know you can adjust the toe but I thought that was all.

*edit* I found it.

I have already rotated the tires and got the same results. Next I am going to try and swap in another drive shaft, and also swap over some steel rims to see if the rims themselves are shot. Then I will try to rotate the half shafts around to see if that helps. I'll post the results here in a day or so.

 

good luck my friend..
its probly isnt the rims since you dont feel the vibrations in the steering wheel.

some part of me is thinking hmm the drive shaft could be mounted differently then when it was removed.. but then the rest of me is screaming half shafts and sub frame alignment.. for all you kno you didnt bolt the diff all the way back in. or a mount or soemthing is bad.

 

I don't know. I tried moving re-bolting the drive shaft every way it can be. I doubt it is a mount or something because when I parked the car everything was good. So it has something do do with what I have done recently. I haven't gotten a clear answer on this yet, so, will bolting the half shafts up in a different orientation than they were cause a vibration? As I said before, I did not mark anything when I took it out.