wrd1972

I have been tracking down a driveline vibration for weeks now, but have finally determined that it is coming from the rear of the transmission and has nothing to do with driveline angle.

When you drive 70 MPH on the street and the vibe starts, if I push the clutch in to disengage the motor from the transmission, the vibe remains. This tells me the vibe must be between the tranny and the rear end and should not be related to the motor.

I have had the drive shaft balanced by one shop and verified by a second shop and the DS balance is dead on. I replaced both u-joints too, both of which actually showed damage to the plastic disks inside the caps as well as scoring on the ends of the journals. No apparent reduction in the vibes by replacing these u-joints.

For testing purposes only, I have the driveline angles set to zero meaning the crank, tranny output shaft, drive shaft and pinion are perfectly in-line so there is no chance of driveline angles causing the vibe. It's a straight shot from the harmonic balancer all the way to the pinion. BTW it required shimming the transmission up 1/2" in order to accomplish this. To do this, I placed a pair 1/4" square washers between the tranny mount and the tranny crossmember to raise it. Once the vibe is terminated, the pinion will be set to -2 degrees.

I currently have the car up on jack stands with the rear suspension loaded for testing. I also have the wheels and rotors off and the vibe remains when going 60 MPH in the air. There appears to be NO abnormal run out on the axles.

I then decided to place an impact gun on the gas pedal to get it to run a constant 70 MPH to induce the vibe, then crawled under to find the vibe. I put my hand on the rear end and felt nothing. Put my hand on the back of the transmission and it is vibrating like mad. This is clearly the vibe I feel in the seat when driving over 60 MPH on the street.

I can also visually see some flutter by the front drive shaft yoke where it inserts into the transmission while the vibes are occurring. I put a dial indicator on the yoke and there is a bare minimum of .020" slop which allows the yoke to move up and down. Assuming the DS is properly balanced, clearly there appears to be problem with the tail shaft bushing. I also noticed that there are very few markings on the front pinion yoke that one might expect to see, right where the yoke might rub the current bushing. That is another indicator of a worn bushing, at least I would think.

I have already purchased the Rockland gear bronze "no walk bushing" and it is ready to be installed. It definitely fits nicely on the front drive shaft yoke plus it is longer so it should provide even more support for the yoke than the original. I plan on removing the transmission tail shaft housing in the next day or two.



I am now very optimistic that once the bushing is installed, the vibes will be gone. If even then these PITFA vibes remain, there must be some freakish issue with my drive shaft which will immediately be replaced by a decent aluminum shaft.

Wish me luck. I will post my results.

97pontta

Keep us updated with your results. I developed a driveline vibration after my M6 swap (A4 was smooth) and also suspect the tail housing bushing causing my driveline vibrations. I've triple checked the pinion angle and replaced the u-joints with no change. I also can feel a little slop in my tailhousing bushing, but havn't measured it as you did. I was planning on having the M6 rebuilt soon so I hope the new bushing helps the vibes.

wrd1972

Well I have the Rockland bushing installed and everything back together, but I don't have enough transmission fluid to test it tonight.

Some information on the Rockland bushing (T56NWB). I had a transmission shop remove the old bushing and press in the Rockland bushing into the housing using the proper install driver to ensure it does not get goober-ed up going in. The housing went back together without a hitch.

The clearance with the old bushing and front DS yoke averaged .012". The clearance with the Rockland bushing averages .0015" which is considerably much more snug and desirable. The drive shaft slid right in the transmission effortlessly without requiring any hammering like I read in a few other posts. This dude really fits snug.

When I try to move the front drive shaft yoke up and down like before, it moves less than .002" which is another terrific reason to remain optimistic. I will definitely be testing the setup tomorrow.

wrd1972

Drove the car today with the new Rockland bushing and the reduction in vibes is significant over 60MPH. :chug:

There is a very tiny amount of something still there and I am convinced it will come down to fine tuning the balance of the drive shaft. If it is not a tiny balance issue, I can safely say it must be the normal stuff to expect from the rearend and tunnel mount TA. I am going to cut the suspect weight off of the rear of the DS and try various size washers along with a big hose clamp to dial it in. I did this with my jeep and had good results.

It is now no longer annoying to drive the car like it was before. The Rockland bushing is a success and I strongly recommend it if you have vibes like I detailed in this post. You can get it from Rockland but you have to call them, its not on the website. It costs $35.00 plus a ridiculous $16.00 to ship it. Installing it was a piece of cake.

BTW these are the driveline angles I am currently running:

97pontta

Glad to hear the bushing solved most of the issues. I'm not expecting to eliminate all of my small vibrations as I also have a tunnel mount torque arm and poly transmission mount. With those two items your going to transmit more road noise and vibration that stock, but I'll do the bushing replacement while having the tranny rebuilt.

wrd1972, a little off topic but how do you like your 9 inch rear? I don't have a Midwest but have a Moser. I've been battling extreme gear whine since I've had the rear, had it setup with a new ring and pinion from a local shop and still is loud. Does yours make much noise?