littledog

Yes this is another drivetrain/driveshaft clunk thread.

Initially I thought my rear differential mount was bad as there's a clunk when I let out the clutch. Therefore I filled it with urethane. All other mounts have minimal movements except that one.
But now I can hear/feel a clunk when I let out the clutch AND push IN the clutch. The clunk feels like it's towards to back of the car.

So what is causing this clunk? I searched and it looks like it could be the driveshaft carrier bearing or U-joint or CV joints? Or it could be from the dual mass flywheel?
But none of the thread talked about hearing the clunk when pressing the clutch in...

Thanks in advance as this clunk is driving me crazy!

EDIT:
Additional information:
After driving around more I can feel/hear the clunk whenever I get off or get on the gas in gear. So I guess that rules out the flywheel.
It feels like it's coming right underneath the area between the front & rear seats.
So does this sound like the U-joint or carrier bearing?

EDIT X2:
Okay finally got the car on the hoist and took a look. The center driveshaft has little to no play so it rules out the carrier bearing? Also there's barely any movement when the clunking can be heard/felt so that rules out the mounts?
You can actually repeat the clunk coming from the rear differential just by keep letting the clutch out/pushing it in. It almost sounded/felt like it's coming from inside the rear differential. It clunks whenever there is load change in the rear diff (i.e. from neutral to engage clutch in 1st or changing gears).

Has anyone else experienced it? Do I need a new rear diff? If so, which one will fit my car? It's a 99.5 5sp. I searched and it seems like I should have a DAJ?

Any help is appreciated. Thanks in advance.

jaimesonlee

I have the same problem and have been researching but not much luck. I'm gonna be doin an engine rebuild on my A4 and plan to find and resolve this issue during that time.

Pete@ECSTuning

I've had this same issue in my old A4. Low rear diff fluid. I had the tiniest of leaks through an axle seal. Give it one more winter and my diff was nearly half empty. Not much for the oil to cling to after the diff so a leak that seemed small was indeed much bigger.

You may want to consider some Redline MT-90 - click here - I have had fantastic luck with it as have many many others. It even helped mellow out a bit of a 3rd gear crunch I was experiencing. The drain is fill is incredibly straight forward - one drain plug low and one fill plug up high, though you will need to attach a hose to the nipple on the bottle since you have to squeeze the new oil in like a turkey baster.

littledog

I checked the fluid level and it's at full.

Thanks for the suggestion though.

Pete@ECSTuning

You checked your rear differential fluid? How? There isn't a dipstick.

littledog

Loosen the fill plug on the diff on a hoist. The level is right at the bottom of the fill plug/hole.

jaimesonlee

I refilled my rear diff with RL 90W and the clunk is still there plain as day. I think its either the drive shaft to rear end joint or some slop in the rear end itself.

littledog

The noise seems to be coming from the part closer to the front in the differential. However since the system is interconnected it's really difficult to pinpoint where is it coming from exactly. But it does sound like it's from the internals

I'm bringing it to a VW specialized shop tomorrow to get a second opinion. I will post up results once the problem is identified (or fixed). Thanks.

littledog

Okay the VW shop says there's some "backlash" in the rear differential. Basically there's a "gap" so when the center drive shalf turns the rear axles don't turn right away. So there are some play between the gears/pinions in the rear differential.

Long story short I need to get my rear diff rebuilt or get a junkyard diff (which could have the same problem). Not looking good

Thi

ooo no, sad to hear. I have the same prob as well. The only thing that I haven't replaced back there are the subframe mounts.