Rear-end "Thump"

**Jas11n** · 27 March 2005, 11:39

Originally posted by dan_b

I've been noticing this for a while, but was assuming it was my vigourous driving style, but now I'm becoming a regular passenger in my car, you start hearing/ feeling things that you just ignored/ accepted before...

I'm getting a very strong thump from the rear of the car on most gear changes. It's especially bad in 1st - 2nd, and generally gets better as you go up through the gearbox. It's also less bad if you're really really gentle on the clutch/ accel, but any amount of rashness in one's left foot and THUMP...

I'm presuming it's something to do with the rear diff - is it basically knackered? How much do they cost to replace? Anyone got one?!

I've also noticed just how bad the off-throttle transmission shunt is too. It really is awful. I replaced the rear diff mount last year with the Powerflex bush, which has made little to no improvement in all honesty, and has made apparent a huge and awful transmission vibration at 1500rpm. To cure this, is this just a simple "snub-mount" bush jobbie? I'm seriously considering swapping the Powerflex bush back to a normal rubber one at the same time.

I "used" to have this thump (very much worse in 1st to 2nd gear changes),,,. Before I wrecked the car I went down a couple of different routes.
First off I thought it was the rear box thumping somewhere, so replaced the rubber hangers for the OEM "chain enclosed in rubber" ones. Nope still there. I made the mistake of replacing the whole diffmount bush and bracket with an OEM one(more on this further on), but again the thump remained. I then bought the powerflex mount and this made the whole thing worse

and I got a horrible vibration at 1500/2000 revs along with the mother of all drones coming from the back on the motorway at 70+ mph (not fun at all having to tootle along at 60/65mph) IMHO not a good mod if you don't ever track the car and need a bit of comfort on the motorway.
Then the crash happened,,,,,,whilst the car was in getting sorted, I've had the gearbox mounts replaced and also the rear wishbone bushes and subframe mounts done. Thump has now gone. I think it must be have been a conbination of all those that has sorted it,,,,,,no a very good answer, but seems to have worked in my case.
I still had the vibration and drone, so I removed the powerflex bush and replaced just the bush, "without" replacing the alloy bracket it's held in that Audi will sell you, telling you the bush isn't available on it own,,,,,,Rubbish!! it is!! part number 171 199 214 D. Check your family album for a list of what this bush fits to

(I could list it here but it's as long as my arm)
All vibration and droning is now gone, no-more thump, and the gearchange has no shunt felt through the gear stick, change more precise and positive.

HTH in some way Dan

**dan_b** · 27 March 2005, 18:43

Well, I'm definitely considering removing the Powerflex rear diff mount what ever happens, the way it has worsened the vibrations in the car at 1500rpm is unforgivable in my opinion. Glad it's not just me who has experienced this either. That has been a totally sh*t mod IMHO.

I'm also pleased to hear that your solution didn't involve a complete replacement of the rear diff itself! If basically it's down to all the rubbery bits all finally collapsing, and you've basically replaced them all and that cured it, I can totally accept that. The car is 14 years old, has been driven hard and the bushes will all be shot. I need to replace the front suspension bushes too, so maybe I just get the whole lot done?

**Beetie** · 27 March 2005, 20:04

For the price of them you had might aswell change all of the bushes. Im sure they arent that much to buy..... Maybe Ben could tell you.....

**porkkis** · 27 March 2005, 20:26

Fourrings, have you purchased the bush with that oe number? I have and the bolt hole is not in the middle as it should be! Have I been sold (collected) a wrong part or what?

**Jas11n** · 27 March 2005, 20:38

Originally posted by porkkis

Fourrings, have you purchased the bush with that oe number? I have and the bolt hole is not in the middle as it should be! Have I been sold (collected) a wrong part or what?

Yes,,,bush was exactly the same as the one supplied in the alloy casing.

**porkkis** · 27 March 2005, 20:39

So you're 100% certain the bolt hole was in the middle as in the original bush?

Graah! Have to get another one then

**Jas11n** · 27 March 2005, 21:07

Originally posted by porkkis

So you're 100% certain the bolt hole was in the middle as in the original bush?

Graah! Have to get another one then

Yep 100% certain,,I watched the guy's fit it at my local specialists

**porkkis** · 27 March 2005, 21:31

OK, thanks. This was valuable info for me.

**Jamo** · 27 March 2005, 22:42

Originally posted by dan_b

Well, I'm definitely considering removing the Powerflex rear diff mount what ever happens, the way it has worsened the vibrations in the car at 1500rpm is unforgivable in my opinion. Glad it's not just me who has experienced this either. That has been a totally sh*t mod IMHO.

I'm also pleased to hear that your solution didn't involve a complete replacement of the rear diff itself! If basically it's down to all the rubbery bits all finally collapsing, and you've basically replaced them all and that cured it, I can totally accept that. The car is 14 years old, has been driven hard and the bushes will all be shot. I need to replace the front suspension bushes too, so maybe I just get the whole lot done?

I think there's nothing wrong with the mod, i think it will highlight the state of your other bushes, just like if you uprate your wishbone bushes and you notice your top mounts being worn.

After a 3 week period can't notice a difference between the two in terms of comfort (defo less shunt) or vibration but i'm running standard springs.

**slow2** · 27 March 2005, 23:02

I have been driving around with this mod ( power flex diff mount ) for 5 months with no problems

**martinjs** · 28 March 2005, 00:24

It got rid of a lot of shunt for me too, agree with jamo though. It will highlight the next 'weakest link'. Deffo change all the bushes, also gearbox and rear diff mounts. I did a rear diff swap at the garage meet which initally made a big difference but then a bit of shunt returned but this was down to fitting a dodgy diff!

Dont forget these cars are getting old now so things will start to wear and turning the boost up or fitting fancy turbos just puts more stress on the drivetrain.

**s2driveruk** · 28 March 2005, 03:19

Dan, I had exactly the same probs as you until Tom changed my clutch and also renewed the gearbox mounts and sorted the snub mount when re-attaching the box.

There is definately a massive positive difference to the whole feel of the transmission and less off throttle shunt too. It also completely removed that awful vibration through 1-2nd gear in the revs u mentioned as i was about to change back to a standard OEM rear-centre diff mount.

**MikeNZ** · 28 March 2005, 06:10

I had bad shunt as described -very difficult to change gears smoothly. Replacement of the two matching diff mounts (three in all - the powerflex mount replaces the other one) totally cured the shunt. The gearbox mount was new. I had clutch judder too but replacement of the engine and sub-frame mounts cured that as well.

**Jas11n** · 28 March 2005, 06:52

Oh,,,,,forgot to say I had the snub mount changed too.

So,,,,,,looks like I may have a goosed rear diff then ? ? ?,,,,,,damn it,,,,I can't afford this,,,,I've spent just over Â£3k so far, in 2 months

Rear-end "Thump"

Rear-end "Thump"

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