Scooby92

alexm1994

I would make sure the driveshaft u-joints were new or in excellent condition in addition to the driveshaft being straight and balanced for higher speeds. Your change to a higher gear ratio results in higher driveshaft speeds especially on the highway where any imbalance will be felt.

856SPEED

Setting up gears is a job for someone who really understands differentials....there are shims/proper backlash, etc. etc. Hopefully it was installed correctly.

Although what was mentioned above may the culprit as well. I would assume you also changed the batwings and half shafts as well. Those could be a problem (u-joints) and what was mentioned; the driveshaft as well.

WVZR-1

You most likely needed to change the slip-yoke from your A4 to a D44 shorter drive-shaft OR you used a D44 drive-shaft from an early 4+. If you transferred your A4 slip-yoke to a shorter D44 shaft you need to check the dampner on the A4 slip-yoke and it should have been balanced before use. Make sure the u-joints are seated correctly into the pinion flange, at the short-axles and at the spindle flanges.

Regardless the combination used the drive-shaft should have been balanced and assembled with new u-joints.

Scooby92

Mr. Peabody

What WVZR-1 has described is exactly what I had done to my 95 A4 when I replaced my Dana 36 for a 44. You should get the drive shaft re-balanced. If the place is several hours away give them a call and ask what they charge.

GREGGPENN

Does this mean anyone swapping u-joints needs to balance their DS? I've had a mystery shimey...that comes/goes above 65-70mph for years. I replaced one of the two u-joints in 2010 but never considered the need for balance.

I have, however, wondered if I installed the DS using the correct orientation. (I've tried reversing it a couple of times). By now (29yrs), I probably should replace the other u-joint (OK...BOTH THIS TIME)...and see what happens.

If balanced, will mounting orientation matter?

alexm1994

No it does not mean you have to rebalance your driveshaft after replacing u-joints, you are probably using the same parts from your car. But in my opinion if you are to perform a D36 to a D44 swap using a used driveshaft purchased on-line it would be a good idea to have it balanced and checked for straightness. It has been a while but the times I've had a driveshaft balanced it has costed less than $100.00 each time. Remember I did say that there will be higher driveshaft speeds with higher numerical gear ratios which will exacerbate any imbalance in the shaft. This is a possible problem with the OP vehicle. Hopefully there is no problem with the rebuilt differential.

WVZR-1

Swapping the parts that you swapped you can't bypass the 'balance operation' - If you used the slip-yoke from the A4 and it still had the dampner on it I'd suggest you buy new slip-yoke without the dampner and reassemble with a balance. I can't imagine someone experience doing the change and NOT telling you that it needed a balance. Now if you handed him parts and said 'do this' then it's on you!!

I know two fellows that if they do 2 u-joints in a performance drive-shaft application won't do it (with a guarantee) unless it's balanced.

Scooby92

MatthewMiller

First things first: get under there and make sure every bolt for the diff and batwing is tight, as well as trailing arms. Also, make sure the joints in the halfshafts are good.

Does it only do this in 6th gear? Does it only do this under power, or also when coasting? If it does it when coasting, does it do it when it's also out of gear (or the clutch pedal is pushed in)? If the issue is a balance problem, then the vibration should happen at the same road speeds regardless of what gear you're in or whether you're on the throttle or not. If it only does it when you're on the throttle, I'd be inclined to suspect one of the six u-joints.

pologreen1

Just for a point of reference... before I had D44 parts swapped in I bought thick gear 3.73 sets and the installation at corvette specialty shop was "above their limits these days"

The Rear was too old, and too complicated according to them.

I am not positive anymore, but I thought there were some slight differences in the cases from an old standard 9", or 10 Bolt, etc,.

A shop by me charges $300 to change gears on a mustang, and $1200 for the c4.

bought D44 and never looked back.

hopefully there is no difference in installs and if there are hopefully there is no damage being done.

Did your mechanic suggest a "break in"?