Volhv

I was underneath the car, and quickly spun the driveshaft in a jerking motion, And I think My clunk is coming from The area where the two differential halves meet. Maybe The splines on the coupling are worn out. (item 25) Odd that it just slides on there.... nothing retaining it.

I have the typical clunk during gear changes, throttle lift off, or sudden acceleration. I've replaced the diff with another used one (due to a stripped fill plug), and the clunk is the same. One would think it's a different issue than, but I'm 99% sure it's the diff....... Maybe propshaft carrier bearing.....
I'm thinking of taking the nose section off the diff, and greasing the splines.... see if that does anything..... but it might just be a waste of time.

oh... and I also urethane filled the diff mount.

Anyone know figure out the reason a lot of us are clunking?

Prospeeder

Well you have tried anything with the mounts. That front mount is notorious for clunking from the rear the same way, the diff will slam up and down, most people from what I read seem to be buying a power ring and making them a solid mount to eliminate all the movement. The diff mounts at the rear can hog out and cause excess diff movement.

I would really really doubt its the piece your referring to could cause this.

Volhv

As mentioned above, I did make the front mount a solid one with windoweld.

You are probably right, that the coupler is most likely not the cause of the clunk, but I do hear a noise coming from that exact area, when under the car, and moving things by hand.

I'm thinking of windowelding the driveshaft support bearing also. See if that makes a difference.
I can now deflect it a fair bit by pulling it, but the rubber appears to be in good shape with no cracks. It's super pliable...... but I don't have a reference to know what a new or good one should feel like.

Prospeeder

So you think the urethane is really holding it firmly enough that its basically solid? Did you check the 2 mounts at the rear part of the diff? If the center support rubber is not split and ripped, I dont think it would thud, if its enough to thud you would think it would hammer/vibrate on hard acceleration. Im actually fighting the same thing on my A4. I think its inside the diff like the back lash too much

Volhv

It's definitely solid. Filled all the voids.... no movement. The 2 rear mounts are in good shape. I made some solid ones for that one too but did not feel the need to install.

Center support bearing mount for the driveshaft did have cracked rubber, cleaned it up, and gave it a strengthening coat of urethane.

After all this, my clunk has decreased significantly in frequency and intensity. But, it still does it.
I'll look at the tranny RH side mount next. I have a new one ready to go.

About that coupling..... I replaced my diff with a used one. Did not make a difference in clunking.
Out of the car, they both behaved the same. If you swiftly turn the input shaft, a clunk can be heard from the area where the coupling is.
To confirm it's not a backlash issue, I removed the nose peice off the old diff, and tried to replicate the noise by turning the pinion..... no noise. It's definitely a issue with the nose peice or coupling. After I put it back together, the noise was gone. Some fluid dripped on the coupling and splines. I think this is taking up the play.

Unfortunately I discovered this, after I installed the new diff, that clunked too. Reason for diff swap was stripped fill plug, but I managed to remove it now that it's out of the car. Someone must have used a 3/8 or something instead of a 10mm.