Still Fighting with front brakes

Hey guys, I've gotten some great help with bleeding my brakes, but I still have a problem that's kind of wierd.

If I pull on the brakes, I get pressure and the bike will stop fine. However, if I hold on to the front brake (like on my sloped driveway) the front brake gradually loses pressure and eventually I roll backward.

I thought that this was still an air problem, so I kept bleeding the lines and adding new fluid while pointing the bike down the drive way. But it did the same thing pointing downhill.

then I held in the brake while in the garage, and it did the same thing.

Any ideas??

One thing I am worried about is this:

when I was putting the plunger back into the master cylinder I nicked up the 2nd rubber gasket. I am wondering if that is letting in air when I hold the front brake under continuous pressure?

Hope not, I am not sure how the seals all interact. There is no fluid leaking out and no air bubbles in the master cylinder when I open it. But I can't explain it.

would this type of thing happen just with air bubbles still in the lines?

I remember the classic symptom of a bad master cylinder is just what you described: you can get good pressure with a fast pump, but slowly over time the pedal will go to the floor and you lose the brakes as the fluid bleeds by the piston. If the piston and seals are not holding, they will let pressure bleed off.

Am thinking this repair kit would resolve the issue, but would double-check part number before ordering.

Click here > M/C Kit from Z1E

Good Luck!

Yea, it's called bypassing. I replace many master cylinders at work because of this problem. Fluid is actually getting past the seals when pressure is held for awhile. It will stop fine but as you said, sitting with the brake on causes the fluid to be forced (slowely) past the seal. Your "nicked" seal is most likely the culprit.

Dammit:angry:

I pulled the thing out because it was so gummed up it would not slide. then I had a bear of a time getting it back in.

Will order one today and try it out.

mucho gracias!

IowaKZ wrote:

...it was so gummed up it would not slide. then I had a bear of a time getting it back in....

Perhaps a rubber cup was just "swollen," because it should not be difficult to slide either cup into the bore.

Good Luck!

I never thought about the cups being swollen. It's possible. I took it apart and cleaned it up and tried to put it back in right away. Maybe if it had dried out some it would have fit better.

I guess to clarify a little more: I had a hard time getting it started. Once the seals were through the opening, it was easy to push back and forth.

However, getting it started was difficult. When I tried to push it into the hole, it would mushroom out and get stuck. I ended up using the shop vac to suck in the rubber gasket. However, with all my pushing and pounding before that I know I did something to the seals.

I called Z1 and ordered a new one. They said it would still ship today.