Rear Differential - thumbing noise

[vtraudt]

Rear diff has mean making a thumbing noise under load (like teeth jumping) that got worse and worse over time.
Started in hard acceleration in low gear in turns.
Now even normal acceleration makes it 'jump'.

This is on 2003 RS6. I had the same experience on a C5 Allroad a few years back.

Finally took the rear diff out and opened it up. No obvious catastrophic damage that I could see, but certainly some dark oil and metallic sprinkles.

Teeth look 'grooved'.

a) does the shown wear marks explain the 'jumping' noise?
b) if so, how is the wear making the sound?
c) if not, what is causing the noise?

[IMG][/IMG]

http://www.audizine.com/gallery/data/500/image0023.jpg

[Mad Cow]

I have the same thing, thumping at low speeds when accelerating. I doubt it's the diff, that would probably be a catastrophic failure situation. My guess, at least in my case, is the driveshaft support bearing. I can imagine a bad bearing would let the driveshaft flop around a bit at low speeds when there's less inertia in the driveshaft. But I'm not an engineer so it's just speculation.

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[Scotty@Advanced]

That pinion gear looks about right. If there is any thump coming from a rear diff, that usually indicates play in something a bearing or something. Any play should be evident when opening up the diff. BTW that diff has quite a bit of wear looking at that magnet.

[PZ.]

Mine was a bad U-joint in the center of the driveshaft.

[vtraudt]

Now, with a the rear diff replaced, we still have the thumping noise. Failed to inspect the center support bearing, so that is next.
But from various posts, 'thumbing' in low gear, high torque is often caused by worn center bearing support.
Is the RS6 prop shaft shared with the those from other 4.2 C5 (A6, S6, Allroad), or specific to the RS6?



One number I found:
Part Number: 4B3521101D
Supersession(s): 4B3521101B; 4B3-521-101-B
DRIVE SHAFT.
Fits A6 , A6 Avant, A6 Quattro , RS6 , S6

Aside from buying new OEM or aftermarket shaft, are there any other options?

If rubber off the center support looks shitty, I will try a ghetto fix with 3M window weld (can't hurt).
Also trying to find local company that is skilled to take OEM shaft apart, replace bearing/support (and re balance if needed), but have little hope (I think I tried years back with prop shaft for B5 A4 and ended up putting a good used shaft in).

[Nollywood]

Propshaft is common to all C5 V8 tip models.

[Mad Cow]

There are a couple shops that will rebuild your driveshaft if you send it in, but they likely won't have any in stock. Advanced Automotion sells new ones the cheapest I've seen, something like $650. That's compared to the $550ish and rebuilt and $750ish new from everywhere else I've seen.

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[bethridg]

034 Motorsport sells a replacement support bearing.

https://store.034motorsport.com/driv...i-chassis.html

I just went through this exercise after having the new bearing sitting on the shelf for a couple years.




Before starting, use a paint pen or marker to mark the shaft position in multiple spots for re-aligning during re-assembly.

You will find a lot of threads referencing grinding down the open end of a 17mm wrench to access the bolt holding the two halves together. I had problems with stripping the bolt head following that method. Instead, I recommend you grind down the boxed end into kind of a spoon shape. This will give you good contact on all the bolt head surfaces. Slide a pry bar or similar in the joint for leverage. Making sure the drive shaft is held straight, you can "scoop" the box end wrench passed the u-joint and on to the bolt. You're only going to get about a 1/4 turn at a time. Use the pry bar or a large screw driver between the bolt head and u-joint to press the shaft out. Some people have used a "wedge" and hammer. Repeat until separated.

Then use a hydraulic press and bearing separator to remove and replace the support bearing. Re-assembly is reverse.

Take the opportunity to inspect both CV joints & boots. Repack or replace as needed.

[Scotty@Advanced]

If you have the shaft held together with a snap ring or welded you cannot take it apart.