[pbaker]

A few years ago, a small rock got stuck in my in rear caliper causing the rear wheel to eventually lock up. Unfortunately, there were no fault indicators warning me of the problem. I had to replace the pads and rotor. After installing the new parts, the ABS system kept engaging and not releasing the rear brake. Using the GS 911, I was able to use the ABS diagnostics and clear the problem. All seemed to be functioning properly. Unfortunately, the problem occurred again a year later where it was obvious that the rear brake was engaging and not releasing. This time the caliper showed signs of excessive heat with the aluminum piston partially melted. Replaced the caliper, rotor and pads a second time. Flushed the system in accordance with BMW procedures. The brakes appeared to be fine, but ran into the same problem last week. Again, no fault alarms indicating any problem. I noticed the bike dragging in 5th gear and could smell the burning brake pads. Obviously, the first occurrence had an assignable cause with the embedded rock. Not sure where to go from here. Could the ABS pump been damaged the first time around? What could be causing this scenario further upstream from the rear caliper (brake line, master cylinder, abs module, abs pump)?

 

[Capt howdy]

Did you replace the piston seals? It it these that return the pistons back inboard when when the brake pressure is released. They may have lost their ability to function under the excessive heat and cannot withdraw the pistons.
It’s also possible that the slider pin is damaged or needs lubricating.

 

[pbaker]

I didn’t the first time, replaced the entire caliper with a low mileage used one the second time. I am planning to replace all the seals this time around.