My 89 has developed a roaring sound above 30 MPH that is constant and increases in volume with speed. At highway speed I can put the car in neutral and the sound does not change. My rear CV boots have been torn for some time now. I was wandering if those joints will sound like that when failing?

 

Right Rear bearing? If it become a lumpy sound you will need to act quickly.

 

Brendan sounds like he has the right idea, I second this suggestion of RR wheel bearing failure.
First make sure the big nut is tight if it is then the the bearing is the next thing to replace.
If your CV joints are in question its better to just buy a complete set of rebuilt half shafts, these should last the life of the car
Rebuilts have new CV joints and boots and run about 275.00 per side make sure the CV bolts are tight and check them after 75 miles use blue locktite on them as well

 

Wheel bearings usually have a whirling sound...this sound is dead constant. No variation in sound what so ever. But on other cars when the CV joints go it has a clicking sound...no clicking here.

Does that still sound like a wheel bearing?

Thanks for the replies so far.

 

I think a wheel bearing can have a whirring sound. Its all in the details - and, for conversation's sake, the structure of the piece going bad will determine its sound. I think that the description you give about whirring, which is a word use describe a cyclical idea - is simply a precursor to what they sound like when they REALLY go, which is very bumpy and cyclical as well - only much more severe.

If you think of what TT bearings sound like when they start to go - its a round, constant sound as well - and when they get worse, you can hear separation.

We could all be full of ****, as well. The rotor could be hitting the parking brake and making a constant rushing/roaring sound.

Since your car is an auto, it could also be Converter bearings starting to go, and you simply have an aural sensitivity to only hear it in the way you are currently.

 

Dean, I've had the tires do that when they get into the wear limit indicators in the tread.
Amazing roar. Felt certain it was wheel bearings.
But it was an old set of pilot sports on a set of rims that I'd just stuck on the car to try it out.

But yours are fairly new still, right?

 

Replace the boots and clean/pack the joints as part of the effort. Cheap and not too tough. You'll see on the ***** if they are damaged, and ispect the tracks they run in too for galling and'/or discoloration (blue to black) that would indicate wear and overheating.

Rear wheel bearings start off with a gentle cyclic moan that progresses to whirring and finally a rumble. The noises tend to get louder as the speed gets higher but generally don't change pitch the way tire noises do. Noises from the back of the car like this are funny too. Sitting in the driver's seat you really have a tough time localizing the source; Get someone else to drive while you spend some quality time in the back listening.

FWIW, you may be able to get some more hints by getting the car on stands and listening under the back while the wheels turn. The bearings won't care much about driveshaft angles or wheel loading, so they can usually be heard nicely with your mechanic's stethoscope on the housing.

 

try engaging the parking brake and see if the noise changes you might have a failed retainer shoe spring

 

If you decide to go economy and repack them, its straightforward.
I just finished a spare set this afternoon.
This time, I bought a replacement pressure washer pump and hose. Rigged up a bucket arrangement to flush and irrigate the outer (unopenable) CV with mineral spirits with the splines pointing up towards the sky so it drained. Quite the time saver.

Did a rinse with a whole new fresh gallon of mineral spirits after cleaning the system. Then a final manual rinse.

 

Thanks guys for the input...I will let everyone know soon.

 

If it turns out that the wheel bearing is bad, I'd recommend replacing the bearings on both rear wheels. After replacing the passenger side bearing, I wound up having to replace the left side bearing 2000 - 3000 miles later. Once I knew what a failing 928 rear wheel bearing sounded like, it wasn't too hard to identify it the second time around

 

i get that sound every now and again but its in an 83 928S and its the fuel pump in the tank but from what i understand S4 dont have a pump in the tank!

 

the bad wheel bearings that I have had would change tone or go away in a right or left turn depending on the side

 

Got the half shafts out today...but they don't look like any I've seen. Notice the toothed ring...others I've seen do not have this. Do I have the correct shafts??? I do think they were replaced at some point.

BTW...the roaring is the wheel bearing NOT the CV's...but these are out and they need to be done.

 

the toothed ring is for the ABS quite normal , but a bit dirty
Follow the WSM for CV rebuild procedures