fl3sh

Hi everyone,

I've been lurking these forums for a while, am really excited about the level of knowledge and the willingness you all have to answer questions and troubleshoot. Great stuff.

Anyways, I've had my A4 ('00) for a few months now and have put about 5K on it. Overall the car has 149,000 Km's. Over the last couple weeks a sound has been growing in the back end. It tends to be negligible until you hit 60 km/hr, at which point it's a low hum. By 80-90 km/hr it's a very loud hum with some light vibration- the noise is constant and almost sounds like friction from something spinning.

This weekend my father and I put it up on the hoist, suspecting rear dif (pardon my ignorance I'm not that great with cars- I THINK we were looking at a dif). There was some minor oil leaking in the back, so we popped off the overflow cap expecting it to be empty but it was not. The oil seemed clean with no residue or metal.

We also put the car in neutral and made sure all the tires spun freely and inspected for wear or rubbing somewhere. Nothing obvious. Brakes look new, doesn't seem to be any rubbing there. Tires have a decent amount of tread left- seems like too much noise to be a tire.

Any ideas? I can get up to highway speeds and record the sound if that's helpful.

Thanks in advance!

Phil

kf3506

check the wheel bearing.

fl3sh

Is there a way to check this myself? I had planned on taking it in for a service this week, could potentially tell them to check it while they're at it.

kbonarek

Definitely sounds like a wheel bearing. The go around 70-80k. So you'd be on your 2nd set already (150k). Passenger side typically goes first. Better off doing them both at the same time though.

A simple but not always effective way to tell is to drive the the car until you hear the noise. At a steady speed, load the car from side to side. Enough to put a decent ammount of weight on the rear wheels when you're turning. When you load the car from side to side, it'll make the noise going one way (turning left for example) and then dissapear going the other way (turning right). It doesn't have to be aggressive turning, but enough to load the car. Highway on/off ramps work well.

The rear bearings are pressed into the uprights, btw. You'll need a wheel alignment after replacing them. Autopartway has the kit (with bolt). The inner race is stepped and can only be installed one way...pay attention to that when you take it apart.

voodooca

Just had my passenger rear wheel bearing done - about 7-10km after getting my car.
The noise started out as a hum only at certain speeds and progressed to the sound getting louder almost as soon as I started driving. Obviously I cannot hear your sound, but based on the threads that I read everywhere else - wheel bearing is likely the best place to start.

I didnt have any luck being able to "load" the bad bearing and hear the sound change depending on the side... If I put the back seats down you could clearly hear what side mine was coming from.

If you are able to press the bearing out of the upright without removing it - you shouldnt need the alignment.

Chad

fl3sh

Great stuff, I'll check it out- thanks again.

guy with the a4

Also, be sure to check the coil springs in the back.

My car is doing the exact same thing in the rear left, and my bearing is perfect. Upon further inspection I found a hunk of my coil spring missing, very sneaky problem to have and it could cost you a lot of money replacing the bearing without fixing the problem.

New spring is 140$ from the dealer here (Quebec)


HOWEVER. Do inspect the bearing, easiest way to tell is to push on the top part of the tire really hard with your foot, if the tire moves and there is a clicking then it's a broken bearing. But that is a iffy test, that will show a very broken bearing, not a breaking one. Jack the tire up, wiggle the tire in the same way and then spin it. If it moves or grinds when you spin then replace it.