Your opinion needed... Do I have rear brake dragging?

[Apostle]

I need opinion and advice from experienced mechanics. If you do not know what I'm talking about, please do not answer and flood this tread.

Last weekend during the long day ride I noticed that my rear brake disk was hot. When I said "hot" I really meant it. I couldn't keep my finger on the disk surface more than 2 seconds. At the same time when I checked the front break disks they were absolutely cold.

Initially I tried to convince myself that I was using brakes agressively and that's why the are hot. Still, I decided to do a clean test... I waited until the disk became cold, then I rode for about 1/2 mile without breaking, then dropped my speed and stopped without applying any brakes. Still, the rear brake disk was hot.

At home I removed rear brake pads and cleaned everything around brake pistons. There is no corrosion, no leaks or anything that would indicates mechanical brake problems (I keep my bike clean and service it according to specifications) . I assembled rear brakes back and ran the same test as above (without braking). The result is the same -- rear brake disk is hot.

Now I'm wondering if that's related to the brake pads that I changed about a year ago (I can't believe that I rode whole year with hot rear brake disk without noticing this! What a moron!)

A year ago when I replaced rear brake pads, I didn't buy original BMW's pads, but bought "Carbone Lorraine RX3" brake pads (part number 2900RX) that I read about on this forum. The difference between original BMW's pads and Carbone Lorraine's was the amount of brake dust left on the wheel. The brake disk wears faster with Carbone Loraine pads, because of the harder brake pads materials. The price difference between original BMW's pads and Carbone lorraine's was significant, so I was OK with additional dust on my wheels (I wash my bike once a week anyway).

QUESTION_1: I never checked the temperature of the rear brake disk when I had original BMW's brake pads. Can somebody who has original BMW's pads installed verify the rear brake disk temperature while riding without heavy braking?

QUESITON_2: Is anyone using Carbone Lorraine brake pads? What is your experience? Did you also notice a high temperature on the rear brake disk?

QUESTION_3: What esle should I check in brake system to eliminate a possible brake dragging? Could it be related to a possible ABS mulfunction (I have an ABS version of R1150R).

Thank you in advance for your answers,
Apostle

[boxermania]

Yes, you do.

This usually comes about by dirt collecting under the dust seal which will not allow the piston to relax and move away from the rotor once the brake is released. You might get away not having to rebuild the caliper by removing it from it's mounts and carefully cleaning under the dust seal....no guarantees though.

[Apostle]

...
You might get away not having to rebuild the caliper by removing it from it's mounts and carefully cleaning under the dust seal....no guarantees though.

Thanks for reply, Boxermania! How do I clean under the dust seals? Should I remove them completely? (And how to remove them?)

Thanks,
Apostle

[jcridge]

The rear brake pads are two different thicknesses. Are you getting scoring and heat on one side of the rotor and not the other?

When you return from the test ride, try to spin the rear wheel. If it seems rather hard to turn, crack the rear bleeder to see if residual pressure is holding the pistons. This will tell you if the ABS is holding, rear master cylinder problem, or rear brake line is failing.

The rear disc temperatures of a dragging brake will be hot enough you will not be able to touch the rotor with your fingers...trust me. Plus the rotor will be discolored. If you can hold the rotor for a few seconds, its not dragging that hard, and following boxermania suggestion to clean the dust may help. You may want to get two dust seals in case they don't survive the cleaning. If you remove the pads and carefully pry back the seals. you can vacuum and blow the dust out.

John

[mozark]

Before doing anything else, try this little trick that someone else posted on here. "Burp" the excess pressure (or vacuum) in the 2 accordion shaped boots on the slider pins on the rear caliper by raising the edge of each boot off the slider pin momentarily. My R1150R did the same thing after I had the rear caliper off to clean it up and this trick fixed it. Please let us know if it works on yours.