Huge brake problem after M50 swap

[SmokinTires]

Alright, so I got my M50 in the car.
During the process I changed over to an iX brake booster with an e34 M5 MC. I bled the brakes and all was good until I started driving it around the block. The brakes worked a couple of times, maybe 10 stops or so, and the pedal became harder and harder to push. I also noticed while at low speeds shifting, the car wanted to stop. I take the car out of gear and then the car comes to a complete stop pretty damn fast with out me pushing the pedal.

I figured out that the rear brakes were staying locked up. So I went to the MC and loosend a brake line to relieve pressure, and then they unlocked. I found that the MC lines were backwards, switched them around. This worked for about 10 or so stops again, locked back up, again .

For the life of me, I can't figure out what is causing this. I did't put the proportioning valve back in (the one that sits below stock 87' 325iS MC), but this SHOULDN'T be causing the rear brakes to stay locked up, instead the front tires should be easier lock up, right? Also, the BMW TIS website diagrams don't even have the proportioning valve in any of their diagrams.

Help me out please!

[NickP]

Did you put in the one way valve to the vacuum line? If no, put one in - if yes - it sounds like you have it in facing backwards.

[SmokinTires]

The check valve right? This currently isn't on the car although the vacuum line is.
The car creates the most vacuum at idle, that being said, if I let the car idle again it will get easy, that is until the rear brakes lock up and stay locked up.

[Ryan Stewart]

Is it an instant change or does it progressively get harder like when bleeding brakes.

[SmokinTires]

Progressive

[SmokinTires]

Well, I went and installed the check valve for shitz and gigglez, it did seem to help the problem out, but I still can't push it on flat ground. It seems as if there is still some pressure in there.

[UNHCLL]

disc or drum rears?
sounds like a bad caliper

[SmokinTires]

Disc rears. The reason why I think its not a caliper is because, both sides lock up at the same time :?: Could be but I doubt it, I won't rule it out. If I loosen a brake line up front to relieve pressure the wheels spin freely.

I think I should try to put the proportioning valve back in and see what I get, maybe its also a relieve valve of some sort.

Right now I'm open to anything.

[BahnE30]

put the check valve back in,
it also might be the MC itself i had the same problem only with a stock MC get a new one should solve the problem,
if you don't have the coin drive for another mile and you should be to go after that, or atleast thats the way mine was all but lock up all four wheels then drive through it and it would be fine until you shut the car off and started it back up

Disclaimer: MAY CAUSE SEVERE WEAR ON PADS.
i ate a brand new set up in a week so i up graded to ceramics fuck organic shit

[SmokinTires]

Yeah, I put in the proportional valve back in, same problem.
Even though my M5 MC is brand new, its getting a new one tomorrow.
I'll post the results.

[RedBaron86325]

had the same problem with mine. I ended up rebuilding the rear calipers then used a pressure bleeder....no more problem.

[SmokinTires]

Its wierd that both would go out at the same time, right when I change the MC. The only reason why they stay locked up is because pressure can't get back to the remote mount res. If I loosen a line at the MC all pressure is relieved and rear brakes unlock. Which leads me to believe its the MC.

[E30-323ti]

Bimmubushi had this same problem on his hybrid beasty.
I think he posted the solution here or on bimmerforums.
Do a search.

[DaN]

Take apart the mc and see if everything looks in place, seals, springs, etc...

[SmokinTires]

Haha, easy fix! It was the clevis on the iX booster, its about 1 inch longer than the stock iS clevis. I have never read anything about them being different. I noticed it right as I was getting ready to pul the booster. I swapped them out, works properly and stops like a dream!

Thanks for all the effort though!