Sponginess in Brakes

[jcorbs]

My 98 has had excessive pedal travel since I got it a year ago.

I've replaced pads and rotors and thoroughly pressure bled the system three times.

The car came with braided aftermarket lines, and I have successfully bled my MCoupe and other car systems many times without problem.

If I hold my foot on the pedal when I start the car it sinks at least an inch, and requires at least one pump to come up to full pressure while driving. Once the pressure is pumped up, brake response is fine.

What am I missing? Booster? Master Cylinder?

Thanks

[thejlevie]

With the engine idling, does the pedal sink if you hold a good bit of pressure on it for 20-30 seconds? A sinking pedal would probably indicate a problem with the master cylinder if there are no leaks. Otherwise you could be looking at a booster problem.

It is normal for the pedal to sink at engine start if vacuum has bled off the booster. That can easily happen over night, but if the engine has recently been run there should be plenty of vacuum still in the booster. A leak or bad one-way valve are possibilties if the vacuum is lost too quickly.

[CowboyTurbo]

Sounds like the MC.

[jcorbs]

Thanks folks. Is there any way to check the MC without pulling it?

[4ZPN]

http://forums.bimmerforums.com/forum/showthread.php?t=511884

No solution, but it offers some insight.

[SleepRM3]

I had the same problem on my '97 M3/4, and I found my RF stainless steel brakeline was leaking brakefluid.

When you bled the system three times--did you bleed your clutchline also?

[jcorbs]

I had the same problem on my '97 M3/4, and I found my RF stainless steel brakeline was leaking brakefluid.

When you bled the system three times--did you bleed your clutchline also?

Yes I did. Interestingly, very little air the first time on any of the lines and nothing the last two bleeds.

Also had a friend pump the brake pedal while bleeding, and bled with eth engine running. Very minor improvement after both.

[jcorbs]

http://forums.bimmerforums.com/forum/showthread.php?t=511884

No solution, but it offers some insight.


Thanks. An interesting series of posts. Some really good experience out there!!

[SleepRM3]

Looks like Stoptechs are the answer. $5K solution for a 4-wheel Stoptech kit!

[smokindav]

Is there any adjustment in the linkage from the brake pedal to the master cylinder? I've got the E36 M3 low brake pedal too.

*Scrambles for the Bentley manual*

[jcorbs]

Looks like Stoptechs are the answer. $5K solution for a 4-wheel Stoptech kit!

I have their front only kit on my MCoupe and it is more than enough, and properly sized to balance the stock rears.......$1,995

[savage217]

bumping this thread. I have the same issue with my pedal sinking and feeling all spongey. Did you guys ever figure out a fix? In the track section people are saying they replaced their boosters and it ended up fixing the issue contrary to traiditonal beliefs that a sinking pedal/sponginess would be a bad master cylinder. :eyecrazy