urS6 vibration

[JayEll]

Greetings!

My urS is having a serious vibration and I'm running out of ideas what to fix..
Basically everything is nice and smooth until I reach 40km/h after that vibration gets worse and after 60km/h it starts to get better.. I'd say and guys who have been driving that car say that vibration seems to be coming from the rear..
Additionally it doesn't have any effect which gear/revs I'm driving, vibration is present.

I just bought this recently and I'm not 100% sure what has been done before me but just by looking under I would say that 90% of the parts in suspension, rods etc seems to be changed.

What I have done until now is:
Tried another tires from my A4q, no effect.
Changed rear differential, no effect
Inner CV joints to rear, no effect
Changed prop shaft with new center bearing, and joints in both ends + balance, vibration moved from 40-60km/h to 60-80km/h..


What I heard from Old LMS (Finnish VAG specialized tuning / repair company) repairguy he said that for these C4 A6's outer CV joints sometimes got so stuck that they did serious vibration. I have ordered new outer CV's and I guess I'm able to test them next week at the latest.
Meanwhile I'd like to have some more ideas what to check. Thanks in advance.

[diesel des]

I had a vibration once and when I lifted the car on the ramp and left it running in gear I could see a front drive shaft was slightly bent. At certain speeds it would resonate. Worth a try. Beware of moving parts during this test.

[moggies]

Have you tried swopping wheels front to rear and see if transfers to the front?

[220bhp]

Possible wheel bearing or sticking rear brake calliper.

[HMS-S6]

My S6 has always had a slight 'funny' vibration too, comes in at 100 or thereabouts and is like a low pitched thrum through the car. I've seen 150ish a few times and everything visually underneath looks ok so I don't worry too much about it!

[JayEll]

Have you tried swopping wheels front to rear and see if transfers to the front?

Yes, and I tried totally different set of wheels from my A4q. No changes.

I had a vibration once and when I lifted the car on the ramp and left it running in gear I could see a front drive shaft was slightly bent. At certain speeds it would resonate. Worth a try. Beware of moving parts during this test.

Thanks for idea.

Possible wheel bearing or sticking rear brake calliper.

Thanks, I've to check these out too. Brakes are new but I guess there might still be something wrong..

My S6 has always had a slight 'funny' vibration too, comes in at 100 or thereabouts and is like a low pitched thrum through the car. I've seen 150ish a few times and everything visually underneath looks ok so I don't worry too much about it!

Yeah well, this is not funny vibration It really makes car undriveable between that speed range.

[JayEll]

Outer CV's changed to back and no difference..

So basically everything from gearbox to rear tires has now been changed.. Only time we have had some difference is when we changed prop shaft. Then vibration moved from 40-60km/h to 60-80km/h speed range. For me this sounds that the prop shaft is the problem BUT since this has been balanced by company specialized in prop shaft balancing and other machining works I don't know what to think..
Also wheel bearings were checked and they seemed to be in good condition.

Guys are going to drive car today in a car lift to check if they can point out the part which is making me and my wallet go nuts, I keep you posted..

[moggies]

May still be the prop? Was the replcement 100% tested before fitting?
Otherwise there isnt much left, unless there is a diff issue?

[JayEll]

I'm pretty confident that it is a prop issue but we're still checking if there's something we haven't noticed..
Replacement shaft was fitted with new joints & center bearing and after that it was checked in specialized shop. I'm not sure what they have done there but at least they had put a new weight plate to the prop shaft..

Also rear diff is changed. I opened that replacement diff myself and checked that everything is ok. I put new seals in it and new oils of course, this didn't reduce vibration at all compared to original diff.

[moggies]

Unless the prop can be fitted to another car, it cannot be ruled out considering the vibration speed has changed. The machine to balance the prop is in a dead straight line, where on the car it may be close to straight and constantly changing angles with the suspention.

[JayEll]

Very true.. Guys are about to take prop shaft out for more detailed check today.. I'll take this to different shop for quick balance check and if there's no other options, we'll install this to different UrS to see if vibration moves there.. We'll see..

[JayEll]

Good news, vibration is gone!

This other shop checked the balance of the prop shaft and they discovered that it wasn't balanced at all.. in addition center joint needed replacement.. well after these were done, vibration was gone.. finally! Makes me wonder that why didn't first shop see these?? Well, I'm going to ask them to give my money back for this we'll see how that goes..

Anyway, thank you all for ideas and support

[moggies]

[newsh]

Good news, vibration is gone!

This other shop checked the balance of the prop shaft and they discovered that it wasn't balanced at all.. in addition center joint needed replacement.. well after these were done, vibration was gone.. finally! Makes me wonder that why didn't first shop see these?? Well, I'm going to ask them to give my money back for this we'll see how that goes..

Anyway, thank you all for ideas and support

Glad you finally got it fixed! Thanks for letting us know.

[Vorsprung durch Technik]

Great result