I noticed a rubbing sound from the rear brake recently. I removed the caliper and pads, and found when I pressed  the pedal, both pistons would operate to the same degree,and then retract when the brake pedal was released. However, when I refitted the pads, I noticed the offside pad would run close to the disc, hence the sound,  the nearside pad would contact the disc but on releasing the pedal pressure, the pad would retract twice the distance as the offside pad. I pumped the pedal a few times to try and get the nearside pad to stay closer to the disc , but it would always retract more than it needed to . My guess is that the offside piston is sticking therefore when the pedal is released. the retraction "action" is pulling the free piston back more. I have ordered a kit. 
Anyone had the same problem? The hoses look good, I get good pressure on the pedal so hopefully just crud in the caliper.
On a perfect set up, given that the pads are not physically attached to the pistons, as they are on some car calipers, is it normal to hear some slight contact noise? Both my front pads/discs have very slight contact noise. 
given the age of her, I may as well do the front calipers too.
Thanks for any replies
Bob

Sounds as if the caliper has lots of sticky goo in it and the piston is stuck to the seal and as the pressure is released the seal returns to normal and takes the piston back with it instead of leaving it nice and snug to the disc.

Hi Rick, I guess the answer will be obvious when I split the caliper. Do the o rings need any sealant, or just a drop of brake fluid. I will do the front calipers as well, for piece of mind.
Thanks 
bob

Just lubricate with a splash of brake fluid. Take care removing the pistons as some are hard anodised alloy and the anodising cracks easily.

RicK G wrote:Just lubricate with a splash of brake fluid. Take care removing the pistons as some are hard anodised alloy and the anodising cracks easily.

Surprised Rick didn't mention it, but easiest way to remove the pistons is with a bit of compressed air.

As above, just be very careful. Wrap the caliper half in a towel or something equally soft to stop the piston taking out the family cat, or worse, breaking the piston.

I just use a flux capacitor.

I could " wedge " the easier piston, and use the master cylinder to free the sticky one, or I could use  a piece of threaded square section and  wind out a bolt to grip both internal sides of the piston.
Cannot beat a bit of Heath Robinson, alternatively a walk up to the local garage to us their air line.

I would not try to grip the piston from inside, it would distort and probably hang on even harder. Wedging the free one and pumping the other will most likely work

Pumped the pistons as per Rick G , and they came out fairly easily. Bores were clean although one piston was a different colour. One was dark grey, looked like it was Teflon coated, the other a lighter colour. Both in good condition, so reassembled and bled using my hand vacuum pump. Both pads are now close to the disc, so will test drive tomorrow. Thanks for the help. Onto the fronts now
bob

Been a week since I reassembled the rear caliper. I can still hear a rubbing sound, which goes away when I apply the brakes. The brake action is not particularly impressive, so, after finding an odd piston in the caliper, I will replace both pistons, and fit goodridge hoses too. One of my front pistons has been damaged during a previous removal, so the good rear piston will be fitted in the front. I must remember to check for adjustment free play at the master cylinder prior to bleeding.
has anyone noticed the benefit of fitting stainless hoses over new std BMW hoses.
bob

Stripped caliper again, fitted new pistons with a dab of red rubber grease,  refitted and bled. 
Brake action is now more positive but can still hear a slight rubbing sound, which goes away under brake application. Checked caliper action and both pistons act and retract together. 
My rear caliper requires two o ring seals, caliper part no 20/4367/00, but my fronts only need one, Motorwerks service kits only ever supply one. Will send them the details and fotos.
After each ride, I spin the wheel, and there is no drag or signs of overheating on the disc., just the normal light sound of the pads against the disc. 
Hmm so what else could it be?
Have thought about possibility of the driveshaft rubbing on the swing arm housing if there was play on the universal joint.
I checked the final drive bearing and found when gripping the wheel at 12 and six  o clock, there is a hint of movement, but not at nine and three o clock. When  i rock the wheel at 12 and six o clock, I can hear a very slight click, which i think is the disc moving the pads very slightly. In terms of movement on the final drive bearing it can only be about a couple of thou at most. 
is this amount of play acceptable, the bearing doesnt seem to be noisy, or should I strip and refurbish ?
Ear plugs in, radio full blast, noise? what noise?
Bob

What you can hear is normal. With new pads etc they will touch very lightly as you dont want to have to move your pads far before you start braking. It's good as long as nothing is overheating and you said it isn't.

My rear brake is now working as it should, although the rubbing noise can still be heard occasionally during brake application. I now think it is coming from the final drive unit which I got from motorworks. There is very slight play on the main bearing, perhaps this accounts for the noise. Thinking back, I cannot remember hearing it with my original final drive. The unit is oil tight and doesnt overheat, have added it to the " to do" list for the winter.
Thanks for all the replies.
Bob

RicK G wrote:I just use a flux capacitor.

But you will need 1.21giga watts to use that  


k-rider