f80 m3 rear brakes...

[facuf80]

okay so hopefully someone can help... ive had a weird metallic rattle squeak sound from the rear. one thing i noticed is the brake pads like sit lose, if i reach behind the wheel and grab them i can shake them around. i took it apart and noticed that when i push one of the pistons in the other dosent come out? on my last F80 i did brakes and when i would push in one side the other would come out. do i need to bleed the brakes? or???

[2kaccordocoupe]

Sounds like a sticky piston. Take it apart it may need a cleaning and lube.

[FlyingLow78]

Originally Posted by 2kaccordocoupe

Sounds like a sticky piston. Take it apart it may need a cleaning and lube.

What exactly do you lubricate a sticky brake piston with? Brake fluid?

Stock rear brakes have rubber dust boots to keep dirt and pad material from damaging the pistons and bores. Assuming the boots are not damaged, the pistons shouldn’t be in need of cleaning. They’re designed to get filthy and really hot without adversely affecting their performance.

Pushing one caliper piston in is going to displace fluid through the path of least resistance. If another piston doesn’t extend, then the fluid is heading back toward the master cylinder. This is not abnormal or an indication of a problem.

Assuming stock rear pads, there will be a small amount of looseness which may be heard as a light clunk when applying the brakes while reversing. Aftermarket pads often have more looseness and clunk.

OP needs to do more troubleshooting to determine the source of the squeak/rattle.