ok i was posting in the general forum but no one really is saying much so heres the problem i just replaced the to rear calipers and the master cylinder i did bench bleed the mc and bleed all the lines from rr,rl,fr,fl. everthing was working fine while bleeding the system and the first 2 mins or so of the test drive then all of a sudden the brakes started to lock up and it got to the point to wear i had to go to first gear to get the car to go still. it finally came to a stop. in the end the pedal was so damn hard i couldnt move it a inch. so in order to get the car back to the house i had to unbolt the mc from the brake booster(lines are still attached to mc)so the preassure would release. used e-brake home. so i'm i going to have to swap in a new brake booster or what . if so can i use the one off my 4 lug s4 donor car (i have a s4 gxl) adivce needed bad thanks !!!

 

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Alright the first question i am going to ask is (did you spin the rear caliper piston all the way in and if you line up the dot on the back of the rear brake pad to the piston) the second question i would ask is if you have your old MC. If you didn't reset the rear caliper it might be draging the brake untill it heats up enought to lock the wheel. THe same thing might happen if you didn't line up dot on the brake pad to the piston. The reason i ask if you have your old MC is that we need the compair the MC piston depth. Sometimes the MC piston depth is different between units. I am not sure why but this happend to me before when i was replace a MC on a corolla GTS. THe brakes would feel higher than normal or harder than normal. THan it would lock up in mins depending on the time of the day. To fix this you would need the adjust the rod that comes out of the brake booster. The rod should be adjustable so you can change the length of it. IN this case you would need to shorten the rod so you wont have so much drag. To adjust the length of the rod you need to hold the side that goes in to the booster with something (vice grip with a rag around it or something like it) and screw the the tip of the rod in with a 7mm wrench. Try it and see if it helps. The way to adjust the booster might be different from cars to cars. If you have any more question PM me. Hope it helps!