Noise coming from rear. Help sought.

[decampos]

There's a frustrating intermittent rubbing noise coming from the rear. It's difficult to describe, kind of like a whine. It's at a constant pitch (the first E note after middle C on a piano). It disappears when I dip the brakes (but then comes back). Also, it's not there when I start the car from cold. Normally appears after 10 mins or so of driving.

I inspected the rear hubs. Nothing seems amiss as far as I can tell but I don't really know what I'm looking for. The brake dust shields arn't particularly corroded/distorted and are not dragging across the rotors (as far as I can tell). The pads were fairly worn so I replaced them but hasn't made a difference.

Any ideas? Any advice very much appreciated.

 

[Arde]

Is it possible a brake pad with wear indicator sound was installed?
Given we have no wear sensors somebody may have used the sound based pads common in other older cars. They do go quiet when you brake.

 

[deQuincey]

check the handbrake
when that happens, without reducing speed, slightly handbrake to check for difference
a mojor work would be to go through the correct tensioning of the handbrake, this is actuating over the rachet wheel in both rear wheels and properly adjust the hand brake, i have found that is useless to tension the handbrake cable only, you must do the complete job

another issue is, when you replaced the rear brake pads, did you check the 20 degrees angle in which the piston must be positioned ? check the blue manuals, you must place the piston at that angle for a proper braking operation

 

[decampos]

Thanks for the replies.

Is it possible a brake pad with wear indicator sound was installed?

No, I can't see anything like that. Certainly doesn't sound like that sort of thing.

check the handbrake when that happens, without reducing speed, slightly handbrake to check for difference
a major work would be to go through the correct tensioning of the handbrake, this is actuating over the rachet wheel in both rear wheels and properly adjust the hand brake, i have found that is useless to tension the handbrake cable only, you must do the complete job

I'll look into that.

… another issue is, when you replaced the rear brake pads, did you check the 20 degrees angle in which the piston must be positioned ? check the blue manuals, you must place the piston at that angle for a proper braking operation

I did see that mentioned in the book. I'll double check that. Thanks.

 

[30csl]

When it is warm can you jack up the rear and with proper safety precautions have someone listen back there for a noise? I did this on a car once and found the culprit to be the brake dust shield.

 

[DTZ]

check the handbrake
when that happens, without reducing speed, slightly handbrake to check for difference
a mojor work would be to go through the correct tensioning of the handbrake, this is actuating over the rachet wheel in both rear wheels and properly adjust the hand brake, i have found that is useless to tension the handbrake cable only, you must do the complete job

another issue is, when you replaced the rear brake pads, did you check the 20 degrees angle in which the piston must be positioned ? check the blue manuals, you must place the piston at that angle for a proper braking operation

I have the same issue. What is the Blue book?

 

[Arde]

I have the same issue. What is the Blue book?

There are BMW binders for every model, the covers are blue, I think it is two binders for the E9. They were for mechanics not owners.
Not to confuse with the Blue Book that has price estimates for every car in then US...