Excessive Brake Pedal Travel - '91 318is

[gibby]

My wife and I bought a 1991 318is 5-spd recently, and I've been trying to figure out a problem with the brakes and haven't been able to get to a solution. The P.O. had the car garaged for a few years, and I bought it knowing it had excessive brake pedal travel.

Here's what's going on:
- If you're coming to a gradual stop, the brake pedal will go down to within 1" of the end of travel without doing a lot of stopping, then the brakes grab.
- If you pounce on the brakes (quick/hard, i.e. panic stop) the brakes grab immediately and the car stops properly.
- Pumping the brakes stops the car fine.

The P.O. installed new pads all the way around in the last year and they do look new. I also can't find any leaks or any other abnormalities. Rotors and other brake components look fine, maybe just a little old.

I've replaced the master cylinder and the power booster, plus all of the rotten vacuum lines under the manifold. I've also bled the brakes using the two-person, pedal/pressure method, enough to cycle through the old brake fluid.

In between one of the bleed attempts, I took the car out and did a couple long/hard stops to try to actuate the ABS system. It's hard to tell if the ABS system is even working, but I heard this can help get trapped air out of the ABS lines.

Anyway, I'm stumped with this one. I'm thinking maybe there's still air in the lines somewhere. I also heard the calipers pistons can retract if the retaining springs on the pads don't seat correctly.

Has anybody seen an issue like this? Should I do a vacuum bleed?

[Dmitry at Pelican Parts]

Hi gibby....sorry to hear that you're having issue with the brakes! I've attached one of our tech articles that hopefully will help you isolate the issue and quickly resolve it. If you have anymore questions, feel free to submit a Comment just below the article and someone will get back to you shortly. Good luck!

E30 Brake Lines - BMW E30/E36 Brake Line Replacement | 3-Series (1983-1999) | Pelican Parts DIY Maitenance Article

-Dmitry

[gibby]

Problem solved today.
I read on another forum that this kind of issue can be caused by a faulty seal in a rebuilt master cylinder. I bought a brand new master cylinder (carquest brand) and installed it this afternoon. The result: perfect brakes and the ABS works fine.
It seems rebuilt master cylinders can have weak seals in between the two inner chambers. If the piston moves slowly in the cylinder bore, the seal will leak, causing the pedal to go to the floor and weak braking. If you stomp on the brakes, it creates enough pressure to swell the seal and develop full hydraulic pressure...but light pressure brings back the leaky seal and mushy brakes.
Having replaced a bad master cylinder in the first place, I never suspected the rebuilt unit would be bad! Lesson learned.
I did buy a pressure bleeding system along the way and can say this makes brake system flushing very easy. Definitely a good buy.

[Dmitry at Pelican Parts]

Glad that worked out for you gibby. Please keep us in mind for future part needs or tech info. We're here to make your lives easier!


-Dmitry