2008 535xiT rear braking

[gmeamtn]

cross post from 5series.net. if not allowed, please let me know asap and i’ll remove. still trying to figure out various forum plates rules.

greetings from snowy northern arizona! 2008 535xiT with a rear braking issue i’m struggling to diagnose. this issue presented last weekend.

when initially driving, there is no issue with the brakes. however, as pressure is applied to the brake pedal, the rear brakes are staying engaged and not releasing pressure. this only happens to the rear brakes. when allowed to sit over a 30-min period, the pressure to the rear brakes dissipates and returns to normal/neutral function until the brake pedal is reengaged. i don’t know if there’s a proportioning valve somewhere that isn’t allowing pressure to return to the master? or is it the master itself? or ABS related?

this issue presented last weekend while driving on very snowy/icy and uneven roads in northern arizona where we’ve had a huge snow year. at the time i noticed the wheels were spinning and there was some scraping over icy chunks in the road. i initially thought it may be the emergency/parking brake and something had been stuck against the cable. however, after inspecting that system i found it to be operational.

any advice is appreciated.