driveline knock/bang under hard acceleration,what could it be...

[Ringsby4]

How do I describe this ? Happens only under hard acceleration,stops when I back off.It's a vicious ratcheting banging vibration not so much noise.Sort of problem I'm scared to bring on too often,as said normal driving,not evident.
I'm thinking CV joints ,driveshaft...
As its a quattro There's a choice of 8 CV joints and are there 2 more in the tailshaft plus centre bearing ??
It was easy to work out with stealth ( sig below ) when I got a similar noise as only one CV joint and a live axle.
What would be the most likely suspect ?
Thoughts appreciated.

Edit: Noise is evident with traction control on or off....

[aluthman]

Check out the condition of all your mounts. I had a similar issue years ago and it turned out my engine mount nuts had backed off on the studs and the engine was just kind of flopping around under the hood.

[mnvwaudiguy]

Check out the condition of all your mounts. I had a similar issue years ago and it turned out my engine mount nuts had backed off on the studs and the engine was just kind of flopping around under the hood.

This.

Also check on your driveshaft support center bearing.

[Ringsby4]

Check out the condition of all your mounts. I had a similar issue years ago and it turned out my engine mount nuts had backed off on the studs and the engine was just kind of flopping around under the hood.

Checked all these when I did an oil change a couple of days ago but good thought.

"Also check on your driveshaft support center bearing."

That or the CV joint on the driveshaft...are there two ? I've never really beamed in on this as its up above the exhaust IIRC

"Check to see if your exhaust is hitting..."

Defin not that,completely different reaction to hard acceleration and gave that a good testing shake when under the car.

I think I have to get the car up on a hoist when Xmas hols over instead of crawling around underneath which is never fun,at least the car is driveable

[Silveravant]

Check to see if your exhaust is hitting the body brace that goes under it in the middle of the car.

[Jeevan]

if CV joints are bad, you wont notice it during high speeds. you will notice it while turning under 10-20mph only. Its hard to say what's the problem without checking


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[Jeevan]

As for now, if you have 2 people test this for engine mounts

Start the the car, hold breaks, put it in the drive and see if the engine is rocking front or back during transition from P-D-R

Transmission mounts are these are solid rubber mounts, so they rarely go bad

I suspect carrier bearing or pinion bearing in the Differential, it could be front or back differential( assuming you have a Quattro)
If you suspect drive shaft noise, remove the drive shaft and drive for the car if 2wd mode for couple days and see if the noise goes away.


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[Ringsby4]

As for now, if you have 2 people test this for engine mounts

Start the the car, hold breaks, put it in the drive and see if the engine is rocking front or back during transition from P-D-R

Transmission mounts are these are solid rubber mounts, so they rarely go bad

I suspect carrier bearing or pinion bearing in the Differential, it could be front or back differential( assuming you have a Quattro)
If you suspect drive shaft noise, remove the drive shaft and drive for the car if 2wd mode for couple days and see if the noise goes away.


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Yep,its a manual with 034 engine mounts.
Have an 034 trans mount which when I looked seems okay.
As to carrier/crown/pinion lash etc,cars never been thrashed and Has had the fluids replaced with premium,I just couldn't believe its that but who knows....
Good thought re removing driveshaft,just thinking what problems that could create ?

[Jeevan]

Yep,its a manual with 034 engine mounts.
Have an 034 trans mount which when I looked seems okay.
As to carrier/crown/pinion lash etc,cars never been thrashed and Has had the fluids replaced with premium,I just couldn't believe its that but who knows....
Good thought re removing driveshaft,just thinking what problems that could create ?

It won't create any problems. Many mechanics do that when they have something to fix in the rear diff or drive shaft. You just have 2wd untill you put it back together.

[Ringsby4]

It won't create any problems. Many mechanics do that when they have something to fix in the rear diff or drive shaft. You just have 2wd untill you put it back together.

Thanks,yep I think that's a good course of action.I'll do it on my good friends hoist ( I'm lucky to have a friend like that )
But one more crawl under the car on axle stands first.I've gotta steel myself up for that , haha I'm 66 but luckily reasonably fit !

[aluthman]

It won't create any problems. Many mechanics do that when they have something to fix in the rear diff or drive shaft. You just have 2wd untill you put it back together.

I’m fairly certain you won’t go anywhere if you do that. That’s why the center diff has to be welded to convert to rwd.

[Ringsby4]

I’m fairly certain you won’t go anywhere if you do that. That’s why the center diff has to be welded to convert to rwd.

But we're talking about converting to just front wheel drive....or am I missing something
Incidentally Adam,Wolfie has been going great guns for the last 3 years since my oil pressure drop fiasco.Thanks again for your help at the time when I was in deep water.
Wolfie just hit 250K Kms ,150k miles in your speak at a guess and just humming along ...

[Jeevan]

I’m fairly certain you won’t go anywhere if you do that. That’s why the center diff has to be welded to convert to rwd.

You are right. I forgot the fact that this is an Open diff.

[aluthman]

With the driveshaft removed, it’s like trying to drive with two broken rear axles. The center diff will try to send power to the rear and you won’t go anywhere.

[Ringsby4]

With the driveshaft removed, it’s like trying to drive with two broken rear axles. The center diff will try to send power to the rear and you won’t go anywhere.

Gotcha,well explained but....damn !

[Ringsby4]

When the CV joint in my Ford turbo ute d/shaft failed it was easy to see and hear with the rear jacked up and in drive.It was pretty bad as it had dropped a ball.I cant do that in this case I'm guessing as with all 4 wheels off the ground and in gear would be pretty hectic with all the NVH and as said the *effect* ( don't want to only call it a noise as its more than that) only kicks in under hard acceleration.

[Ringsby4]

HAPPY NEW YEAR Audiziners ! Lets all hope this is a much much better one...
Crawled under Wolfie to have a quick look before a visit to the hoist.
I discovered that when I hold the input flange on the rear diff and try to rock the tailshaft there is a small,really small amount of movement whereas when I do this on the output shaft of the front diff-nothing.
When I grab the shaft about a foot behind the front diff and rock it backwards and forwards I can hear click click click.Hard to tell from which end or where as it is probably transmitted noise ? Note no click noise obvious when I see the movement on the rear diff.
I don't know if its gear noise from the diff transmitted or what.
The center bearing looks fine as far as the donut go's (hard to see because of heat shield )
I also found this :
Rear muffler looking rearward ,look at the muffler mount -its a heavy welded rod that forms a U and then connects to car with a donut at each end-the tailshaft has been rubbing and in fact worn the rod down.I've never heard any noise which I could put down to this and not the noise this thread is about I wouldn't think-but maybe it is ?.


Closeup of the situation :



No mods to rear of exhaust other than dp and no impacts...
So is this evidence of too much driveshaft movement ?
Are my findings above indicating stuffed rear CV joint on tailshaft ?
What do you think ?

[Jeevan]

Its hard to know how much of the play is acceptable over the internet as you posted no video evidence of that. Keeping that aside, I believe your exaust system is bent somewhere. Drive shaft shouldnt not be that close to the exhaust hangers. short term solution- bend the exaust mounts/hangers and make sure that drive shaft has clearance of atleast 1 inch on both sides of the driveshaft. After this, you need to balance the drive shaft(that rubbing mostly like threw the driveshaft out of balace) assuming your ujoints are in good shape. If you cant afford this, get a used driveshaft from a junk yard and install it


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[Ringsby4]

Its hard to know how much of the play is acceptable over the internet as you posted no video evidence of that. Keeping that aside, I believe your exaust system is bent somewhere. Drive shaft shouldnt not be that close to the exhaust hangers. short term solution- bend the exaust mounts/hangers and make sure that drive shaft has clearance of atleast 1 inch on both sides of the driveshaft. After this, you need to balance the drive shaft(that rubbing mostly like threw the driveshaft out of balace) assuming your ujoints are in good shape. If you cant afford this, get a used driveshaft from a junk yard and install it


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I beg to differ about the exhaust being bent,its exactly where its meant to be.No accidents as the force needed to bend the 10mm hanger would be substantial and there would be evidence on the exhaust components.No dents,scratches,nothing.I've owned the car forever ( well it seems like forever lol ) We've gotta work on another theory.
But yes,I intend heating and bending the tangs when I've got the exhaust off.
As to the balance,the damage is symetrical and linear ( think turned on a lathe ) so balance wouldnt be an issue.
I want to find out from someone who's gone through this if that bit of play I have in the rear is indicative of a stuffed CV without pulling it out,buying another from a dismantler and putting it in.I've enquired as to the driveshaft,luckily there are quite a few available over here from manual 1.8 and 2.0 Q's

[bwdysart]

I beg to differ about the exhaust being bent,its exactly where its meant to be.No accidents as the force needed to bend the 100mm hanger would be substantial and there would be evidence on the exhaust components.No dents,scratches,nothing.I've owned the car forever ( well it seems like forever lol ) We've gotta work on another theory.
But yes,I intend heating and bending the tangs when I've got the exhaust off.
As to the balance,the damage is symetrical and linear ( think turned on a lathe ) so balance wouldnt be an issue.
I want to find out from someone who's gone through this if that bit of play I have in the rear is indicative of a stuffed CV without pulling it out,buying another from a dismantler and putting it in.I've enquired as to the driveshaft,luckily there are quite a few available over here from manual 1.8 and 2.0 Q's

This may not be super helpful, but I was backing into a spot without paying attention and I backed into a tree, exhaust first. Now the exhaust bangs against the drive shaft. And it makes an awful clangling sound, but only while cornering, not during acceleration. From reading the thread it sounds like we have different issues, but the exhaust is bendable


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[cavinmclay]

same problem, hard knocking/ clanging noise when accelerating hard off a stop or very slow roll. hard to even classify the noise as a thumping or clang it’s just a hard felt and noisy vibration

[Jayz691]

Maybe your center support bushing is shot, causing you driveshaft to have some extra play. That could cause it to hit off your exhaust when getting on it, or whenever. Id pull the heat shield off, and inspect your center support.

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[beefski]

I’m having a similar issue with my 3.2l. It’s a definite thump only on hard acceleration. Nothing going over bumps at any speed. It’s not metallic sounding. Anyone with a suggestion before I go to mechanic?


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[Ringsby4]

I’m having a similar issue with my 3.2l. It’s a definite thump only on hard acceleration. Nothing going over bumps at any speed. It’s not metallic sounding. Anyone with a suggestion before I go to mechanic?


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Sorry,my situations the same with no definitive answers but I'm going to fix my clearance issue ( see pics above ) before anything else.Maybe my noise/thump is tied in with that.Of course I'll check the main driveshaft whilst exhaust is off.Probably not going to happen for a week or two as hoist is busy atm

[StylinS-line]

Your drive shaft has paint being milled off it , it’s clearly hitting something , they paint the entire drive shaft lol

My car did the same thing and it was bouncing off the trans cross member , only on acceleration occasionally over speed bumps

[Ringsby4]

Your drive shaft has paint being milled off it , it’s clearly hitting something , they paint the entire drive shaft lol

My car did the same thing and it was bouncing off the trans cross member , only on acceleration occasionally over speed bumps

Yep,I'm coming to the belief that's definitely part/all of the problem with my situ

[Jayz691]

Yep,I'm coming to the belief that's definitely part/all of the problem with my situ

Yeah, the support bearing only had like a thin, rubber webbing around it, so if it tears, it will get sloppy. If the bearing is good, but bushing is shot, this is a good option.Screenshot_20210108-121035.jpg

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[Ringsby4]

Yeah, the support bearing only had like a thin, rubber webbing around it, so if it tears, it will get sloppy. If the bearing is good, but bushing is shot, this is a good option.Screenshot_20210108-121035.jpg

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Great news ! and thanks.As I said back in post #19 my exhaust is in the correct position so my problem is probably exactly this causing bad clearance.
That Co. has some pretty innovative gear for Audi..
https://www.jxbperformance.com/

[Jayz691]

Great news ! and thanks.As I said back in post #19 my exhaust is in the correct position so my problem is probably exactly this causing bad clearance.
That Co. has some pretty innovative gear for Audi..
https://www.jxbperformance.com/

Yeah, the owner us Jay Bullington, hes in my one Audi group on FB. Def some cool stuff, and more to come.

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