Brakes locking up

[E30DK]

Alright ive seen quite a few posts and read most of them but nothing is working for me or im not doing "it" right.

I have an 89 325i with an m50nv swap. I used a Treehouse racing booster with the stock MC. Now that the swap is done ive noticed that after driving and braking regularly for 5 to 10 minutes my brakes are all dragging. If i pop the hood and pull the vacuum line off the check valve (booster side) there is a rush of air then the car will roll by hand very easily.

Ive tried adjusting the clevis on the booster rod and ive changed the check valve for the booster with two different working runs and without fail my brakes will be almost completely locked after ten minutes of driving.

I read someones post saying you have to adjust the booster rod itself but ive tried spinning both sides of the rod with the booster out of the car and they just spin they dont actually change in length.

Someone please help me

[ELVA164]

So maybe I'm way off-base here, but is there any chance the pistons in the calipers are sticky?

[E30DK]

No there is a chance but its all 4 brakes so that seems unlikely to me. The car did sit for a while while i was sourcing parts for the swap, but all four brakes? I only immediately assume the booster because thats the only thing i changed.

[bmwguy325is]

So the only thing the booster does is make it easier to push the master cylinder.
Id still check all four calipers and see if the pistons are locked up IE hard to push back into the caliper.

[E30DK]

well thats not necessarily true because if the rod that strokes the master cylinder isnt at the correct length then it will either not allow the MC to return to the neutral position and relieve brake pressure or you will have a big dead spot in the pedal.
So really im trying to see if anyone else has had this problem and how they solved it?
i.e. spacing the master the cylinder

[bmwguy325is]

So do you have a Bentley manual?

[E30DK]

Yes but like i said in the op i cant seem to adjust the rod length just the clevis

[fronton]

how does the pedal for the first 5 or 10 minutes when the brakes are working properly? Are they inconsistent, or really hard, or have a short travel? How do you know all four brakes are locked up? How have you 'unlocked' them? Then they are locked, is the pedal stuck down or stuck up, or not stuck at all? All of this sort of input narrows the field.

[jlevie]

That is almost always going to be a lack of free play in the connection between the pedal and the booster.

[E30DK]

That is almost always going to be a lack of free play in the connection between the pedal and the booster.

Yea you were exactly right. I ended up making a plastic spacer ring plus gasket to sit in between the booster and MC and everything works perfect now. I have about a 1 inch gap of free play on cold start and then after spirited driving and braking for 10 minutes it drop to about 5/8s of an inch which is perfect to me.

Im kind of annoyed that i had to do this to a perfectly new part from treehouse (even though its actually remanned) but hey at least it works.

[E30DK]

how does the pedal for the first 5 or 10 minutes when the brakes are working properly? Are they inconsistent, or really hard, or have a short travel? How do you know all four brakes are locked up? How have you 'unlocked' them? Then they are locked, is the pedal stuck down or stuck up, or not stuck at all? All of this sort of input narrows the field.

Oh and for people with future problems ill try to add a bit more detail based off these questions.

The pedal feels great for the first 5 to 10 minutes. Car would stop and roll just fine.

I thought it was all four at first because all four rotors were crazy hot, so i lifted the car up and sure enough all four tires wouldnt turn by hand.

No the pedal would not be "stuck" in any position. It would still return to the top but once the brakes started locking it would become harder and harder to push the pedal, because the brakes were already on of course.

I had to of adjusted the brake pedal height like 10 times easy because i kept reading about it on here but honestly all the clevis length does is set your pedal height. Unless the stock e30 rod length is actually adjustable then this will do nothing because the rod (on each side of booster) will jsut spin for days and not change length.

Hopefully this helps future swappers

[dude8383]

Can we get a pic of said spacer?

[E30DK]

I can take a picture of it but its already installed and as much as ive had all that apart over the couple of days i really dont want to to remove it again. The plastic piece is an 1/8" thick and the gasket is 1/16", both are just wide enough to fit between the master cylinder and its mounting studs.