Bearing Noise

[jmbinjax]

I have a '73 GT with about 85K original miles and original rear end. I've had since July '05. I changed all fluids when I got the car. I just developed a "whirring" noise from the rear end. I think it's from the right side - this leads me to believe it's a axle bearing (it's not a clicking) but my experience with bearing noises tells me it's a pinion bearing. The noise is at all speeds, in or out of gear, accel or coast. I can't imagine the pinion bearing going so quickly unless it was run dry or overheated, which it wasn't while I had it and I put about 2k miles on it b4 the noise developed. Any thoughts?

[Dmcbrass]

Sounds like a wheel bearing. Usually a pinion will only make noise when you are loading it. (accelerating or maintaining a constant speed). Since it's a 73, the axle thrust is handled with the wheel bearing. You should be able to hear a change in sound by weaving back and forth in the road. You might also be able to tell which side its coming from by jacking up one wheel at a time and running the car in drive. Make sure you don't have a locking diffential before you try this. If the noise is really from the pinion bearing, it will be present regardless of which wheel is being driven. Occasionally rear wheel bearings won't make a noise when the wheel is hanging in the air (car jacked up). This is because the weight is riding on the bottom of the outer race versus pressing against the top of the race when the axle is loaded. Usually by the time you hear the noise while driving the car, there is enough damage to hear it either way.

[jeff denton]

The condition of the oil can help you see what's going on in any gearbox. The best way to see this is to put a magnet on the rear cover. After a few miles any metal will be on the magnet, metal chunks are scary, a little real fine powdery residue is normal. Bearings going out will throw a lot of metal and it has to go somewhere, a magnet will catch it and keep it from circulating.
Both Opel diffs I've been into had the pinion bearings shot while the others were not too bad.