doolittle

I have a 1983 NA 944 with 99k miles. When I bought the car there was a loud humming noise coming from what sounded like the rear of the car. The humming noise was present at any speed (even when transmission was in neutral), it was audible from very low speeds, but went away when turning to the right. I concluded that the passenger rear wheel bearing was at fault and replaced it. Took the car for a test drive and the humming was still present. I thought maybe I did something wrong in the installation, so I replaced the bearings again (additionally replacing the stub axle, too), being very careful to not put any pressure on the inner race of either bearing. Took the car for a test drive and the humming was still present. Neither of the bearing jobs resulted a change in the humming noise: still audible from low speeds, goes away when turning to the right.

Assuming I have not botched the bearing job twice, I am looking for suggestions on what else could be the culprit for the humming noise.

Thank you!

Dan

royalschwarz

Change the other side. I always thought the humming went away under load, not the other way around.

Also check your tires as they can hum when they start wearing unevenly.

doolittle

Change the other side? Definitely can do that, I am getting pretty quick at changing rear wheel bearings! Tires are almost new (<1k miles).

Dan

odonnell

How loose are the bearings in their seats? My outer bearings were super loose. When I removed the old bearings I could see clear marks on the outer race where they had been spinning inside the trailing arm seat.

thomasmryan

if your rotors have a lip on the outer edge from wear, it can create a ringing type sound. (similar to a wet finger on a wine glass)

doolittle

Thank you for the responses!

thomasmryan - I would not describe the sound as high pitched. Rather, a low-medium pitch humming that dominates the interior the faster you drive.

odonnell - Michael, good question! I had to use a slide hammer to pop the inner bearing out (the new 2nd one), but the outer bearing.... I don't remember with great certainty, but I think it came out very easily. The new one I just installed, fresh from the freezer, almost slid right into place without any help to get seated. The only way to really know would be to pull it back apart, correct?

OK, let's say that the race of the outer bearing is spinning and is the cause of my humming headaches. What is the corrective action? A new bearing with slightly different outer race dimensions? A "new" hub?

Thank you for your input!

Dan

odonnell

The outers are designed to be loose compared to the inners, but the wear marks will be the sure sign they are spinning. I used some Loctite bearing stick, put it around the outer race, and so far it's been perfect.

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944vaguy

First I would make sure the noise was coming from the rear by placing the rear on jack stands and spinning the rears up and listening. ( THIS IS DANGEROUS SO BE CAREFUL ). If it is something that can be heard inside while spinning then you can get even more daring and listen from under the car while your wife is inside spinning it up....!!!!!
I always trouble shoot noise by remembering this, If it is a bearing it will change with speed If it is a gear it will change with throttle load.