w140 grinding coming from rear

[kps70]

Hi - latest issue on my w140 is this.
For several thousand miles now, I've had this low speed grinding noise coming from the rear of the car. It's hard to tell whether it's left or right. So far what I have done is
1. had the brakes checked
2. topped up differential oil
3. changed rear wheel bearings
The noise is only noticeable below about 30 mph. It is still there when I knock the car into neutral. It's not there when I am in reverse. The noise almost disappears when I accelerate. It's really quite noisy at around 15-20 mph when just cruising along without accelerating.
It's bugging me big time.
What next? Help!
Thanks
Kieron

 

[Sp!ke]

sounds a bit weird but it could be tyres... swap front and rears to help rule it out.

have you got adaptive suspension? Just wondering if it could be connected somehow. Could be cv joints or centre shaft bearing. Rubber bushes on driveshaft ok?

 

[grober]

My guess is a problem with the little handbrake brake shoes or their return springs inside the little drum which forms part of the rear disc. I assume when you said the rear brakes were checked you meant the rear discs and pads- you can inspect the handbrake mechanism properly without removing the rear disc.
Hang on a moment you said you had the rear wheel bearings changed were the handbrake shoes /return springs checked then?? Other possibility might be a binding brake cable. the directional thing sounds awfully like handbrake shoes to me. A V8 is going to shrug off a partly jammed on parking brake. Next time you drive a distance put your hand on the centre of the rear wheels. Any binding is going to manifest itself as heat- might pin down which side is effected? Other test is to gently apply the parking/foot pedal while moving slowly along- keep the release handle pulled back to stop the brake pedal locking- then it acts like a little foot brake- listen for any change in sound.

 

[kps70]

thanks for the input so far. I recently changed the rear tyres and it has made no difference, plus the sound does not change when moving across different surfaces. When I said the brakes were worked on, I meant the footbrake; it was taken apart and cleaned. I still tried the test you suggested and applying the footbrake whilst slowly moving forwards and there was no change in the noise.
I double checked when moving backwards, and the sound is not there at all.
It's like a bearing grinding kind of noise.

 

[jonnyboy]

I was thinking handbrake too bearing in mind it doesn't happen in reverse.

Quite a concern its been happening for "several thousand miles" though.....

 

[grober]

It begins to sound a bit like worn differential pinion bearings or loose pinion bearing preload. This might change with slightly different pinion bearing loading between forward and reverse. Time to drain the diff oil and have a look for metal filings ! If its that, with a bit of luck the ring gear may be OK and new pinion bearings and adjustment/preload will correct the problem. Job best left a professional differential rebuilder if its that.

 

[kps70]

sounds promising, if expensive! I'll check out the diff oil.