whered my brakes go?

[87-325ic]

so this morning on the way to school i went to stop at the first stop sign and i nearly ran through it.

My brakes have lost almost all pressure, they still work, but i need to push the much softer pedal almost to the ground. if i ease onto the brakes like coming to a stoplight, then they will reach the ground and barely stop me. if i let up and re-press them they get a little more pressure.

stock brake system, 87 - 325i
No fluid loss whatsoever
Clutch works fine
brakes worked fine all the way home last night.

What do you think this is?

Did my MC finally take a dive?

[e30trooper]

you have a leak somewhere. WHens the last time the brakes were done. and did you bleed them? Check everywhere!

[87-325ic]

i bled everything good a few months back, switched fluids and all. everything was good, super solid pedal since then until this morning. pads and rotors replaced a few weeks ago, all 4 corners. everything was good with that too.
also, when the car is running, like sitting at a stop light with my foot on the brake, i continually lose pressure, and if i push hard/ far enough, i get a real nasty crumbly feeling, its not at all smooth action. then the pedal goes to the floor and has very little power. i let up, it comes back up, and does it all over..
with the car off, i couldnt get that to happen when i tried, it got consistently stiffer, but nowhere what it was before this problem.

[87-325ic]

it feels like alot of air is in the system, but i havent done anything to cause that in a while.
plus, the res was completely full. it almost seemed like it was too full.
i couldnt find any leaks on the pavement under the car either. if it were leaking, the resevoir would be lower.


if i had to guess, i would say it seems like fluid or pressure is making its way past a cylinder connected to the pedal. but i really dont know much about the brake system besides a big cylinder pushes fluid to 4 smaller ones.

so any more help here would be greatly appreciated.

[jlevie]

You have a leak or a failed master cylinder. Ecamine all of the brake lines and calipers for leaks. If you don't find a leak, replace the brake master cylinder.

[E3Oslut]

its the master cylinder seal.. Just swap it out and your good to go.

basicly when applying pedal force the seal forces the fuid out through the lines. When that seal is worn, fluid slowly leaks past it and back into the resivoir. That explains it being so full..

[87-325ic]

sounds right.

do i need to swap the whole cylinder, or can i get away with a long day and a 12 dollar o-ring somewhere?

[jlevie]

Swap in a new or rebuilt master cylinder.

[CorvallisBMW]

If that doesn't fix it, I would replace the ABS pump. My dad had a honda back in the day with the same problem, turned out to be leaky valve bodies inside the abs pump. But first guess would def be the master cylinder.

[Goya20]

same problem but i get some brake pressure mid way i changed my master cylinder and bled all my brakes and inspect the lines. can it b the abs pump and is that that Grey cylinder under the master cylinder?

[E3Oslut]

@87-325ic: Just change the cylinder. you don't wanna be cheap with your brakes.
and its way more simple and you get a peace of mind...

@goya: abs pimp is tucked in the driver side fender next to the Airbox. you should see a bunch of lines going and coming from it.

[87-325ic]

how simple is it? drain fluid, remove cylinder, rebolt new one, attach resevoir, add fluid, bleed?

anyone got some good tips for it..

[E3Oslut]

That is all my friend.. It doesn't get any simpler

[e30trooper]

i got something too. on my most recently bought 325, i have full braking power but fluid is leaking from the MC , would it be that seal? or should i change the hole thing. Its bad asking this becuase a took a ASE class on brakes hahahaha

[E3Oslut]

depending on where its leaking from... I dont think its the seal as even the slightest leak is noticeable in braking force. Look under the resivior and the lines and that may be your leak...