Differential Noise

HB Chris

HB Chris

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Does anyone have experience with a rumbling noise in the rear end? I’ve read it can be caused by the pinion bearing or even rear wheel bearings. It starts at 55 and is speed related and not rpm so not engine or exhaust. Don’t really feel any vibration and drive shaft was completely rebuilt last year, this is on my e12 by the way. Any help appreciated.
 
Does it stop or get worse when you turn quickly side to side at speed? Have you tried putting the car on a lift and turning the rear wheels to see if you can detect a noise?
 
On my F150 the rear bearings make noise and I can change the pitch by swerving at speed. Food for thought :)

HB Chris said:
Going on a lift this Friday. The left/right thing works on front bearings I think. It’s hard to swerve at 70!
Click to expand...
 
Rear bearings can be checked by taking the speed car starts to be noisy, switch to neutral, no accelerator and take low/medium left or right (not too much to hear the tyres noise).
By turning left (not left and right) for some time more mass is on the right wheels and bearings should be noisy. For turning right, the left bearing. Engine is on low revs so will not disturb.

Typical differential noise can be detected by changing load on the drive on the gear going straight. Typically starts on some speed and can become quiet at higher speeds and start again somehow later.
 
Basically rear differential noise depends on load on the differential, so acceleration and engine braking is the test (going straight).

If the noise is changing the reason is in drive (differential, driveshaft bearing or gearbox output bearing.

Wheel bearing test on the rear can be done on the lift by applying gear and listen the free run of the wheel after.
Big deterioration of the bearings can also be checked as on front wheel by moving the whole lifted wheel horizontally and vertically and looking for free movement.
 
no experience, but i do have a NOS conical bearing if you need one.

FS: NOS Differential main conical bearing

new old stock bearing 33121203616. with slight oxidation ( after 45 years....) Runs smoothly. 65 euro Located Netherlands, worldwide shipping. (Shipping to the US is 25 euro without track & trace, 32 with Track and Trace, 35 insured + Track & Trace.) I have, and prefer, Paypal. Regards, Erik.
e9coupe.com e9coupe.com
 
It will be on a rack Friday to check at speed but blue book suggests humming is subframe bushings, interesting.

It makes no difference speeding up or slowing down, turning left and right did not seem to make any difference. Blue book also says bearings would make grinding noise only on curves. I hope to know in two days.
 
LSD ? The lsd I put in my coupe years back made a howling noise at around 40 mph. The faster I went the loader it got.
took that out and had my independent shop guru mechanic look into it. He said it was the bearings in the diff.
My way to discover what is making the noise would be to swap out the side loader. But hey that’s me.

just trying to help
 
I found the rear wheel bearing problem on my son's e34 by turning relatively tight circles at low speed with the windows open in a cul du sac. I was able to reproduce the rumble I had heard in the rear at speed but it was more subtle in the cul du sac.
 
So no bueno today. We will remove d/s next week, check center bearing, etc. Using a stethoscope diff, rear bearings are quiet. D/s doesn’t shake, perhaps bad center bearing, everything was rebuilt last year. Noise very pronounced inside car but not so much outside,
 
I discovered that my auto trans fluid is low. It is almost impossible to determine the level on the dip stick with motor running. I added 2/3 quart and will see if that makes a difference. I haven’t changed the fluid yet so it is needed in any case.
 
Update: new front wheel bearings, trans fluid flushed/changed, have not removed d/s as it was rebuilt and I don’t think it is an issue. I am thinking it is the torque converter perhaps, very frustrating for sure. It only starts at 55mph and up, has nothing to do with engine rpm, I can run it up in 1st or 2nd to 60 and no noise, only in Drive, has nothing to do with load, acceleration or slowing.
 
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