So yesterday I ran into a problem with my Shimano MT500 rear brake on my Calibre Bossnut Evo. The bike had been stationary for about five weeks due to a minor injury. I pressed rear brake the lever and the pistons pushed the pads against the rotor but after releasing the lever the pistons didn’t retract and caused the pads to lock around the rotor. The lever also didn’t spring back to its normal position and remains very close to the bars.
I’ve pulled the brake caliper off and removed the pads. It seems like the pistons are stuck. I’ve tried cleaning the pistons for dirt and grime but still, the pistons refuse to retract into the caliper. Also, the pistons don’t move independently of each other and if I press one of them back into the caliper the other one is pressed further out of the caliper. I haven’t bled the brakes, so I don’t believe that the system is overfilled.
Do you guys have any idea of what the cause of the problem might be and how I can fix it?
Put the pads back into the caliper, and using a plastic tyre leaver to push the pistons back! And then refit and try. If still fault – Are the pads worn? How old is the brake? Do you use for downhill riding? I would next bleed the brake. If pads are worn and brake is old, replace with SLX or XT From riding down hill, pads /rotor generate a lot of heat. Also check the rotor for being over heated blue in colour and also replace.