Brake pedal "slips" ?

[sp0rky]

Ok, ive had this problem for a while now, but its never acted up often until now.

usually after my car had been parked for a while, when i first start it up, i would apply the brakes, it would be firm then id feel a "slip" and it would go down easily then it would be firm again.

Just the other night i noticed it happen while driving, and then this morning after starting it up.

Since ive noticed this problem, the brakes feel a good deal "mooshier" than they once did.

Fluid isnt up to the max mark, but it doesnt look empty either. does anybody have any ideas???

thanks guys.

[BMWL2]

it might be low on fluid or you may have some air in your lines Probably wouldnt hurt to flush your system anyways

[TECH]

The master cylinder seals are probably leaking fluid internally, not holding the pressure. I'd get it fixed asap. Unless you have a leak and the fluid in the reservoir was emptied, you shouldn't have air in the system. You can try bleeding them first though.

[sp0rky]

So your saying the master cylinder needs replacement?

is it a hard job to do??

thanks again!

[TECH]

Originally posted by sp0rky@Jan 25 2004, 12:23 AM
So your saying the master cylinder needs replacement?

is it a hard job to do??

thanks again!

It's likely that it needs replacing.

Hard to do? Not for me. :P It's not hard. You'll have to break the lines loose and unbolt it from the booster, and then bleed the whole system.

BMW brake pedals do seem to be a bit soft compared to others though. If your's feels abnormal, then it is probably the master.

[fuzyfuzer]

my 528 has a soft pedal and had the dealership look at it and they said it was normal had them bleed it when they replaced the rotars and pads but it did not change then i drive my neighbors 540 and it is even softer but when i drive my dads z4 it is hard as a rock i just don't get it

[sp0rky]

ok, im going to try to put some new fluid in, the current stuff is pretty old. My question is... will it hurt to mix different brand fluids? im not sure whats in there now...

also will it hurt to put in the ATE super blue fluid with the current stuff in there?

thanks guys!!

[TECH]

If you flush the system, you'll have all one kind in there anyway. If you simply want to add a little, just as long as it's the same DOT as the other fluid, its ok.
Use dot 4.

[EXtech]

I wouldn't mix the blue with the original. They have completely different characteristics and boiling points. Flush the system to rid of the old and then put in the blue. Have you had any abs/brake lights come on when this "slip" happens? Flushing the system completely and replacing the fluid should help with the soft pedal.

[sp0rky]

I've never had any warning lights except for the occasional brake LT circuit warning that comes on once a month and goes away if i shut the car off and restart it

[EXtech]

just trying to determine if you were having an ABS module problem