Rear disc brake issue- need advise

[bladenbullet]

In a properly functioning disc brake system that has properly functioning hardware and lubed slide areas, the caliper piston settles back a bit after you release pressure with your foot on the brake pedal. That is caused by the square cut seal in the caliper bore that twists back after pressure is released. The pad is then in limbo with no pressure against it forcing a very minimal rub of the pad on the rotor surface. That ever so slight rub is not going to build enough heat to override the air flow thru there that carries the heat away. I have machined literally gobs of rotors in my days at the shops. I have machined where there is maybe a hair's width of runout on that rotor surface. The runout that would then be there is from mounting to a hub and that will contribute to the runout you speak of to help push pad back a very tiny amount. I say warp but a better description is "high spots" and that, when bad enough, will cause brake pedal pulsation.

If this is wrong, I truly hope to hear what I am missing.

Great reply...actually, excessive runout causes a low brake pedal due to increased pedal travel to displace enough fluid to push the caliper piston farther than designed to apply the brakes...

A long term effect of excessive rotor runout causes a thickness variation which results in a brake pedal pulsation...

Upon brake release the square cut piston seal is what pulls the piston back enough to release the force of the pads against the rotor...it is not uncommon to have some contact even after release...some vehicles are equipped with quick take up master cylinders and calipers that can release farther to prevent any drag for better fuel economy....

 

[Rocket Man]

Pretty sure this issue is resolved.....