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View Full Version : Replaced diff mount, still clunks



riccnick
03-30-2017, 02:36 PM
Hey guys, my first post here I think. I have a 2001 B5 Avant with the 2.8 and 5-speed stick. I replaced the rear diff mount (180k on it) with the ECS Tuning mount. First day it was perfect and the entire car was silent every shift. I went cruisin through some back roads and started rowing the gears and had a pretty hard shift. Since then it has clunked EXACTLY the same way it was before. Its definitely in the back. (I replaced the trans mounts too so its not those). Has anyone ever had an issue with replacing the front rear-diff mount? I got under the car to check the bolts and make sure they were all still there and tight. They all were. I haven't taken it back out yet (drive the car almost every day). Anyone have any suggestions? I don't think its the rear diff bushings or snub mount or anything else seeing how I had an almost full day of smooth and silent shifting. Any help is appreciated. Thanks,

Bordom
03-30-2017, 04:09 PM
Definitely the rear diff mount.

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Davdraco1
03-30-2017, 06:23 PM
Even if it's new it will still clunk?

Bordom
03-30-2017, 06:55 PM
Could be the actual bushings at the back of the diff. Doesn't take long to have a peak

EDIT: take a look at your center bearing too. Never know

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Spike00513
03-31-2017, 02:17 AM
Peeking from B6 section, not sure if they are set up the same. There is also two bushings that hold the rear diff crossmember attached to the subframe. Small circular ones. There was an 034 billet insert made (and now a plastic ECS one) that inserts into the voids/gaps of those bushings, to fill them solid with metal. I guess that made sense, because any other option would be much more difficult. Installing an insert requires bolting it in. Versus filling the voids of the bushings with sealant, installing new ones, or installing aftermarket stiffer ones (such as poly) is difficult due to tight space/lack of access, and may even require dropping the subframe down off the car. Which is harder than an oil change.

I have heard that it's possible for Audi rear diffs to develop a play/slop, that makes for a clunk. I wonder if this could be it, for both of us.
Because mine seems to have something like that when shifting, not sure if it's the drivetrain or what. Since the mounts are ALL gone. I plan to replace them either way. Maybe I can start there, to see if it helps. It will probably yield noticeable improvement elsewhere. For example, in my experience, a car handles better when the engine is properly secured, rather than flopping around uncontrollably, since it's a large mass, heavy weight.
I guess IF that doesn't work, I can then cross that off the list and wonder if rear diff is the culprit, or something else.

riccnick
03-31-2017, 11:03 AM
Thanks guys. I'm going to have to get under it this weekend and take the new mount off and inspect it. The stock one was definitely worn out at 180,000 miles when i replaced it a few weeks ago. The rubber was cracked in multiple spots, completely toast! And like I said, the weird thing is that I had NO NOISES whatsoever for a few hours worth of driving and then all of a sudden it went back to the EXACT same thing. This is why I'm thinking the new ECS mount might be bad or maybe it came loose or something? (I did put a socket on each bolt again to check and none of them were loose...) If it was anything else I would assume I would have heard it right away when I replaced the mount and test drove the car, no?

Davdraco1
03-31-2017, 11:29 AM
I have street density motor, trans and rear diff carrier. Ecs poly snub and rear diff carrier. I still get a small clunk I think. Idk what it is. Maybe it's just me.

Believer
03-31-2017, 11:40 AM
The clunk is very likely the driveshaft support bearing/bushing. Specifically the bushing that encases the bearing, that the driveshaft spins in, wears out and deflects under load, causing a loud bang.

Unfortunately it seems the only surefire way to fix this issue is to replace the driveshaft with a 1 piece unit or cough up the coin for a brand new Audi unit ($1k+); Audi did not make the bearing/bushing serviceable nor offer a part to replace it. 034 Motorsports offers a replacement but based on all the info I've seen about it, it is largely a miss.

Davdraco1
04-01-2017, 04:38 AM
I thought the 034 unit fixed the issues....

Believer
04-01-2017, 05:40 AM
I thought the 034 unit fixed the issues....
I've read way more 'it failed in X miles', 'vibrated like crazy' and 'im on my 2nd one' than success stories. Mine is clunking and for the work that is involved in getting the 034 unit to possibly fix the issue, it's not even close to worth it. I'll be replacing with a one piece unit from Scotty at Advanced Automation. My brother uses that unit and it's smooth as butter with just a touch of additional NVH being transfered which is to be expected when the bushing is removed.

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Davdraco1
04-01-2017, 07:59 AM
I've also heard it's a PITA to actually replace the bearing/bushing

riccnick
04-03-2017, 02:15 PM
Thanks guys, I didn't get a chance to get under the car this weekend and check her out. I'll see what I can find this week and report back. I'm really banking on it not being the driveshaft, though. I'm not looking forward to replacing that if I have to

riccnick
04-06-2017, 10:24 AM
So I got a chance to get under the car last night. And these are my findings.

The front rear diff mount that I replaced with the ECS Tuning mount is doing its job. I had the car up on jacks and pulled and pushed the diff in every direction i could and it didn't budge one bit. Before when the stock mount was in there I could physically move the front of the diff by hand. This I can not.

The rear diff bushings look good. Once again, no appreciable movement with me yanking on them back and forth.

The drivers side and passengers side cv halfshafts are leaking a bit where they go into the diff. Also, they have some play in the CV joint themselves, the drivers side seemed a bit worse. Not sure how much play is in a new one, but I could rock the end of the halfshaft back and forth just a hair and it felt like it was moving where it was connected to the diff. I suspect this means the diff bearings are gone?

The next thing I did was grab the pinion at the front of the diff and hold onto one of the axle shafts and checked for play inside the diff. There was more than I was expecting / hoping for... It didn't "sound" too bad, but I probably had 20-30 of total rotation (~15 in either direction) at the pinon before I felt it back at the axle shaft... I'm nervous about this one...

Lastly, due to time constraints, I didn't get a chance to pull the heat shield on the exhaust and check to see if the driveshaft carrier bearing was toast or not. I will have to check that out hopefully this weekend. But at the moment I don't think it would be the "only" cause of the slop in the drivetrain I'm getting...