Bleeding the ABS pump?

#21

This sounds to me like a bad master cylinder, not air in the system.

#22

I rebled the entire system today, got the back brakes to both lock up, but absolutely no front brakes. By "none’ I mean with the pedal flat on the floor you can spin the rotors with no tires by hand.

I pulled the master and it is indeed dead. No pressure at all on the front line. I will be getting another, but see the thread on the general discussion I posted titled “are all master cylinders born the same”.

General question, is it possible that pressure bleeding killed it? It did sit without fluid for 2 years, I’m guessing that killed it, but wanted to make sure my pressure bleeding isn’t a source of death.

-Scott

#23

Undo the two front “in” pipes at the ABS pump. Press brake pedal and confirm that brake fluid comes out. If so, test the ABS front outlet lines next.

I don’t see how pressure bleeding at 10-20psi could have hurt anything.

#24

That wouldn’t do anything because there literally wasn’t any line pressure, period in the front. With your foot flat on the floor, car running or off, you could turn the rotors by hand. When I took the master cylinder off, I put my finger over the rear brake fluid outlet and pushed in the plunger and you can feel the air pressure trying to blow your finger off. On the front brake line, absolutely nothing. Now, I suppose its possible that the ABS unit is also dead, but I’ll try the MC first, since it is guaranteed dead.

#25

The car I bought which had sat for quite a long time also needed a new MC. I’m pretty sure getting one will fix the problem.

#26

BigKeyserSoze wrote:

I agree. I don’t see how that could be the ABS pump, it’s gotta be the MC.

Potentially related… I’ve read in several places that with a used MC, one has to be careful to avoid pushing the MC plunger farther in then it normally goes. As in pedal to the floor is bad. I think that the theory is that the length of cylinder wall in the normal piston travel range is nice and smooth and seals nicely with the piston’s seal, but the cylinder wall beyond the normal piston travel range can rust or be otherwise not nice and smooth. Then if the piston is pushed beyond it’s normal travel range the piston’s seal gets a little chewed up by the normally unused cylinder wall area.

Perhaps when the PO was screwing with the brakes the MC got goofed.

Note that if shit is not wired tight Thur morning, BimmerWorld will happily overnight you parts to CMP.