Noisy rear end ?

I know the 911 isn't a quiet car, that's part of the fun, however ever since I've owned the car (2 years)I've been plagued by a strange sort of drumming/rumbling/droning noise from the rear which becomes evident at about 45mph onwards. (increasing in volume until wind / road noise overtakes it about 70-80mph). It sounds alot like transmission / diff noise, however there is no howl when decelerating or accelerating. It's not the engine as the noise is still there when the clutch is depressed and the engine rev's fall to 900rpm. I had convinced myself that it was road noise / tyre rumble, however, the strange thing is the noise gets louder when travelling down a hill and when bearing right, but quietens when turning left.

I have changed the left hand (passenger side on RHD car) rear wheel bearing and both inboard and outboard CV's on that side, but the noise is still there. I've also changed the transmission oil which didn't help either (did help the gearchange though !!)

I could change the other side bearings and CV's, however I don't want to do this unless I'm sure this is the cause, as usually the bearing that complains is the one under load.

Anybody got any ideas ?

Car is a 1982 911SC UK spec RHD, 118,000 miles.

David

It could be your diff bearings. My car had the same noise before i rebuilt the tranny.
Mike

Have you repacked your (other remaining) CV-joints and changed the gear oil in the transaxle in the past two years? I am an advocate for SWEPCO 201 gear oil, having changed to it about 15 years ago, thanks to Bruce Anderson. The type of noise you describe is hard to localize, but apparently not a serious threat to reliability. Good luck!

The SWEPCO website URL follows and has international distributors listed:
www.swepcousa.com


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Warren Hall
1973 911S Targa

Thanks for the advice guys. The gear oil was changed about 3 months ago, but I don't know when previous to that. I use Castrol Syntrax 75W/90, Swepco's a bit scarce across here. I haven't done any re-packing of the other CV's yet, however I think it's worth doing.

Diff bearings had crossed my mind, but it was the noise lessening when turning left that threw me.

One further thing. I know that there are mixed opinions about doing this, but has anyone changed the diff carrier bearings whilst the tranny is in situ ?

Advice is appreciated

Just to let you know. I took the driveshaft out to repack the CV's, which turned out to be OK. Whilst the car was off the ground, I checked the wheel bearing on the same side and found that turning the roadwheel felt a bit rough. Removed bearing and found severe craters on inner bearing race. Replaced bearing and found noise has totally disappeared, it's like driving a different car.

Just goes to show that diagnosing a worn wheel bearing isn't straight forward, and it's not necessarily the one under load when cornering that is guilty. In this case it was the other, due to fact that 911 rear wheel bearings are double row angular contact bearings that counteract thrust, which means that when cornering, centrifugal forces can load both bearings.

One thought on this one.. has anyone ever changed the ring & pinion? If they did.. 2 choices.
1) If it was a new R&P, they didn't lash it correctly.
2) If it was a used one, they didn't lash it in the same wear grooves as when originally set up.

If the R&P is original, I'll either go with earlier posts, or say that it mighe be wearing.

David, Glad you found the problem ... the good thing about packing the CV-joints is that, like adjusting your valves, it NEVER hurts to do them. I find that there is a lot more neglect in the CV-joint/transaxle oil change area than it is even possible for me to imagine! I get flack about doing the CV-joints when it doesn't solve some noise problem ... but as you found out, disconnecting that axle eliminates everything but that bearing and the brakes!

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Warren Hall
1973 911S Targa