My 1998 A8 has been making sporadic clicking noises when I turn the steering wheel to the left when driving and also a kinda plastic rattling sound from the front passenger wheel when going over bumps. I experience no vibration and only hear the sound when I am driving at lower speeds and have the window or sunroof open. I have 68,000 miles on the car.
I took it into an independent Audi shop and was told my car is the third A8 they saw with this problem and it is the output bearing for the differential (transmission). When the shop called the Audi dealership for a quote on the part they were told that the entire transmission must be replaced. The mechanic then tried to do a search with an aftermarket parts supplier and could not find the bearing. The owner of the shop told me he doesn't have the tools to fix this problem even if he could get the part and told me to try to find a transmission place that might be able to help.

I will probably take it to one or more places for another opinion - but if it is this bearing does anyone know about replacing it? Or perhaps other causes for the symptoms other than the bearing?

the bearings are not an replacement part.

however, are you sure of the diagnosis? have you checked for worn cv's?

if so, i would suggest a visit to skf or similar with the bearings in question, and let them source a replcement for you. no big deal, at the very least they would be able to replicate the dimensions...

If this is indeed transmission, try searching if any aftermarket warranty will cover you. (see if you can buy it for your car miles/age)
Most shold still sell powertrain warranty for a year or 2 since you only have 68k.
It is possible this would be a good investment. :)

DM

I had a very similar noise on my car with higher miles and track events. Last fall I replaced it with a rebuilt axle (with new CV joints) from www.raxles.com for $189.00 plus installation.

That's what it sounds like to me.

You can't buy an aftermarket warranty on a car with a problem. The inspector won't sign off on it.

Agree, check outer CV first, then contol arms, then innner CV. Most any bearing can be replaced, they have numbers etched into them, if a bearing house cannot match then a ZF dealer should be able to get one. Or go to the virtual parts section of zf.com Possible complications are minor selective shim washer adjustments or having to use heat/cold to get the outer race into an alloy housing. I have seen online blowups of these trannys; would probably show what hold bearings in.

Bad bearings typically do not click but make a whirring, grinding or growling noise linear with rotational speed. Since halfshaft revs are less than a thousand RPM at normal road speeds the frequency of noise is low. I'd want to run the car on a lift and listen to the bearing.

If the bearing is really bad, then where did the steel go in the tranny?

I am beginning to think it is with the axle and CVs - the rattling happens whenever I go over bumps and the clicking with steering comes and goes - I haven't heard it in 2 days. The rattling is definitely not a metallic sounding or a whirring - sounds like a loose piece of plastic...

I just heard of the recall on some A8 axles so i will probably get the dealership to look at it for free and give an opinion. I'm also going to take it to a german tranny shop for their opinion...will keep you posted...

How regular is the clicking noise?

Descriptions of sounds do not carry well in words.

This could be linked to play in the bushes at the ends of the steering rack. A combination of some steering load and wheel movement can cause a knock/rattle at that point. Carries well into the car because the rack is mounted on the bulkhead, just behind the dash!

Drive in an alley or somewhere where there is a wall right next to you, roll down the windows.

Then turn the wheel hard right and then hard left like you are scrubbing your tires and report back what you hear. It you hear it click when turning the wheel left, it's your right side and vice versa.

Pretty easy to troubleshoot. Also, are either of your CV joint boots torn?

Hi,

Well it is now three days and no clicking when turning - just the rattling sound when going over bumps. However, when I did have the clicking, it was when I turned the wheel to the left so it is the right side. I had the boots replaced a year ago after the right side fell apart... so maybe it got dirty...

well, no clicking past few days - but it was loud and kinda hard to describe since I haven't heard it that many times. Thanks for the ideas. I am making a list and when I bring it in again I will mention all of these possible causes to the mechanic.

If it is a CV boot rip that has precipitated a CV joint problem, you should be able to note lubricant of a very dirty nature strewn about the inside of the wheel, control arms, and possibly wheel well. That's a quick check, you can then jack up the car to verify.

I just had same problems two days ago bumpy road caused same sounds..while ur car is parked push down on side ur hearing noise if u get same sound its the ball joints making the sound.. u need to get new control arms like paul says

If you find it is the diff bearings after all, they can be changed- and with the "tranny" still in. I had the diff seal go which in turn let the oil out-which in turn cooked the bearings. You need three all of which are available from any commercial bearing distributor. You will find that some of the diff casing bolts are a bit fiddly but its not that hard. My tranny is one not used in US but I bet the diffs are the same. Total cost £85 ($150 or so)plus a nice man with a ramp (essential)