Ghetto rear diff mount mod

Nick Gustas · 01-09-2003, 04:13 PM

Ever since I first drove my S4 back in 2000, full throttle accel in 1st with cool temps would cause a momentary scrape from the rear at around 15mph, sometimes a 1-2 shift would thunk from the rear too. A few other people with 2000s posted about it back in the day, and one guys dealer put in a extra snub mount. For me the scraping went away and the thunk was intermittant, sometime hitting a paint strip on a corner and the edl kicking would make a nasty noise.

Almost since the car was new, I'd also sometimes get a little thunk/jolt about a half second after starting to accellerate, lets say I went from a slightly coasting 30 to a 40 zone and gave it a little gas, there would be a little thunk. It had been getting worse lately.

I checked out my rear diff and cv joints and was shocked at the lack of play in them, it's nice and tight back there!

Very nice, much better than I had expected. What was easy to move was the front mount on the rear diff, I could see where the mount was bottoming out on itself and where the driveshaft to rear diff flange had scraped on the body a little.

Overview of mount, camera shot from pass rear tire area, black I beam looking thing is the diff, aluminum mount closest to the camera is attached to the diff and the other side of the mount is attached to the body. Better overview here

I fixed it using a chunk of 3/8" lexan I had in the junk drawer. This shot is looking up at the diff mount, you can see the little mark on the metal to the right of the lexan block where the rubber of the mount had bottomed out before.

In this shot you can the amount of upward movement allowed by the stock mount. I had to pry the diff down and really push with a screwdriver to get the lexan in there, I don't think it'll fall out anytme soon.

I only drove it a little, but the driveline slop is MUCH reduced and the little thunk/jolt on accel did not occur.

I think the jolt on accel was caused by the slack in the mount causing the torsen to send power to front since the rear offered less resistance. as the slack was taken up power would suddenly transfer to the rear. Just a theory.

WoostaS4 · 01-09-2003, 04:21 PM

After that continuous *thud* during start-up, when cold, over bumps, and after hi revs I decided to check it out. The scorpion was great for 10k but then this rear diff. fitment issue popped up. After many attempts to re-align I can say my fix is more ghetto =) I spaced the plastic exhaust hanger with a neatly cut piece of wood and wrapped new creation with many revolutions of electrical tape. 1) wood will soak water and hold much better than plastic or metal spacing piece and 2) electrical tape holds nice in any weather condition. For the past 6k the car has had no issues whatsover and exhaust actually sits better at rear bumper and at the rear diff. area. Glad to hear another had the same issue fixed =)

Nick Gustas · 01-09-2003, 04:28 PM

If I tuck it up nicely it hits the heat shield near the clamps, I'll set it up better one of these days. Either way the rear tips line up perfectly.

The thunk I had wasn't exhaust related, I've only had the exhaust since may or june or something. Was yours from the exhaust or did it thunk stock?

Kitch · 01-09-2003, 04:38 PM

I REALLY need to do this mod. The little "thunk" drives me nuts. I'm a little lost to exactly where that spot is. Any chance of a little more wide angle shot with a mark where that is?

Aren't you glad you tried to help.

WoostaS4 · 01-09-2003, 04:40 PM

Nick Gustas · 01-09-2003, 05:08 PM

hmmm, I know it's 3/8" thick, maybe 1.25x1.75" It was just a chunk I had, my dad used to bring them home for informal target practice, they'd take quite a beating without damage.

I think a U-shaped piece might do a better job, doesn't matter really, just needs to be tough.

Here's a overview:

Kitch · 01-09-2003, 05:21 PM

Nick Gustas · 01-09-2003, 05:25 PM

SlvrBullet Unloaded · 01-09-2003, 05:30 PM

launching the car last night. Friggin unhealthy to say the least.

Nick Gustas · 01-09-2003, 05:38 PM

If I didn't need to drop the exhaust I probably would have pulled the mount and bolted it solidly, I bet there would be very little noise transfer for the driveline slop reduction. At the very least a properly shaped shim piece would be a good idea. I'll probably run this till it falls out, if ever.

01-09-2003, 04:13 PM	#1
Nick Gustas Senior Member Account #: 3094 Join Date: Mar 2000 Posts: 7,470	Ghetto rear diff mount mod Ever since I first drove my S4 back in 2000, full throttle accel in 1st with cool temps would cause a momentary scrape from the rear at around 15mph, sometimes a 1-2 shift would thunk from the rear too. A few other people with 2000s posted about it back in the day, and one guys dealer put in a extra snub mount. For me the scraping went away and the thunk was intermittant, sometime hitting a paint strip on a corner and the edl kicking would make a nasty noise. Almost since the car was new, I'd also sometimes get a little thunk/jolt about a half second after starting to accellerate, lets say I went from a slightly coasting 30 to a 40 zone and gave it a little gas, there would be a little thunk. It had been getting worse lately. I checked out my rear diff and cv joints and was shocked at the lack of play in them, it's nice and tight back there! Very nice, much better than I had expected. What was easy to move was the front mount on the rear diff, I could see where the mount was bottoming out on itself and where the driveshaft to rear diff flange had scraped on the body a little. Overview of mount, camera shot from pass rear tire area, black I beam looking thing is the diff, aluminum mount closest to the camera is attached to the diff and the other side of the mount is attached to the body. Better overview here I fixed it using a chunk of 3/8" lexan I had in the junk drawer. This shot is looking up at the diff mount, you can see the little mark on the metal to the right of the lexan block where the rubber of the mount had bottomed out before. In this shot you can the amount of upward movement allowed by the stock mount. I had to pry the diff down and really push with a screwdriver to get the lexan in there, I don't think it'll fall out anytme soon. I only drove it a little, but the driveline slop is MUCH reduced and the little thunk/jolt on accel did not occur. I think the jolt on accel was caused by the slack in the mount causing the torsen to send power to front since the rear offered less resistance. as the slack was taken up power would suddenly transfer to the rear. Just a theory.

01-09-2003, 04:21 PM	#2
WoostaS4 Junior Member Account #: 41621 Join Date: Aug 2002 Posts: 1,750	What exhaust ?? I have a scorpion which didn't fit so well in that area . . . After that continuous thud during start-up, when cold, over bumps, and after hi revs I decided to check it out. The scorpion was great for 10k but then this rear diff. fitment issue popped up. After many attempts to re-align I can say my fix is more ghetto =) I spaced the plastic exhaust hanger with a neatly cut piece of wood and wrapped new creation with many revolutions of electrical tape. 1) wood will soak water and hold much better than plastic or metal spacing piece and 2) electrical tape holds nice in any weather condition. For the past 6k the car has had no issues whatsover and exhaust actually sits better at rear bumper and at the rear diff. area. Glad to hear another had the same issue fixed =) __________________ Just call: " Oh Lord Jesus!" He'll get into your heart . . .

01-09-2003, 04:28 PM	#3
Nick Gustas Senior Member Account #: 3094 Join Date: Mar 2000 Posts: 7,470	Borla If I tuck it up nicely it hits the heat shield near the clamps, I'll set it up better one of these days. Either way the rear tips line up perfectly. The thunk I had wasn't exhaust related, I've only had the exhaust since may or june or something. Was yours from the exhaust or did it thunk stock?

01-09-2003, 04:38 PM	#4
Kitch Member Account #: 23416 Join Date: Aug 2001 Posts: 2,734	Got dimensions on that little chunk of lexan? I REALLY need to do this mod. The little "thunk" drives me nuts. I'm a little lost to exactly where that spot is. Any chance of a little more wide angle shot with a mark where that is? Aren't you glad you tried to help. __________________ Kitch 2006 A3 2.0t DSG

01-09-2003, 04:40 PM	#5
WoostaS4 Junior Member Account #: 41621 Join Date: Aug 2002 Posts: 1,750	From exhaust. It hit up against the drivers side diff bolt. __________________ Just call: " Oh Lord Jesus!" He'll get into your heart . . .

01-09-2003, 05:08 PM	#6
Nick Gustas Senior Member Account #: 3094 Join Date: Mar 2000 Posts: 7,470	Lucky day, I have a good picture from this summer that I didn't know I took. hmmm, I know it's 3/8" thick, maybe 1.25x1.75" It was just a chunk I had, my dad used to bring them home for informal target practice, they'd take quite a beating without damage. I think a U-shaped piece might do a better job, doesn't matter really, just needs to be tough. Here's a overview:

01-09-2003, 05:21 PM	#7
Kitch Member Account #: 23416 Join Date: Aug 2001 Posts: 2,734	Kick Ass! Thanks so much Nick. Can't wait to give it a shot. __________________ Kitch 2006 A3 2.0t DSG

01-09-2003, 05:25 PM	#8
Nick Gustas Senior Member Account #: 3094 Join Date: Mar 2000 Posts: 7,470	Post if it helps :)

01-09-2003, 05:30 PM	#9
SlvrBullet Unloaded Member Account #: 2711 Join Date: Mar 2000 Posts: 3,175	Great job...This is actually on my too do list, you wouldn't believe the nastiness I heard... launching the car last night. Friggin unhealthy to say the least.

01-09-2003, 05:38 PM	#10
Nick Gustas Senior Member Account #: 3094 Join Date: Mar 2000 Posts: 7,470	Thanks, I wondered if you had any problems with it, mount is squishy if you push on the diff by hand If I didn't need to drop the exhaust I probably would have pulled the mount and bolted it solidly, I bet there would be very little noise transfer for the driveline slop reduction. At the very least a properly shaped shim piece would be a good idea. I'll probably run this till it falls out, if ever.

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