Strange Front brake problem

[DannyBoats]

Hello. I have a strange problem with my front brake. Whenever the outside temperature is warm/hot, my front brake lever won't compress until I bleed just a little fluid out. In the mornings, or when it's cold out all is well. I read somewhere that there is a liner in the brake hose that can collaspe when it's old. I replaced the hose, but the problem is still there. Anybody have any experience with this problem?

[almarconi]

When was the last time you replaced the brake fluid and cleaned out the master cylinder?

[DannyBoats]

I replaced the pads last May when I started riding it daily. I drained the old fluid then and cleaned the master cylinder too. In the last year I've run several bottles of fluid thru the system with the almost daily bleeding to free-up the lever. When I replaced the brake line several months ago I did it all again. I'm leaning towards getting a master rebuild kit. Maybe there's a seal failure or something. There's not alot to the system; the master cylinder, lines, and caliper. I went over the caliper when I did the pads, it looked fine and works perfect.

[almarconi]

I would take the MC apart, inspect and clean it. There is a small port in the MC that is prone to clogging. You can use a single wire from a wire brush to clean it out. Rebuild kits are not too expensive.

[DannyBoats]

I'll try that. Thanks for the help.

[Colin Green]

I would take the MC apart, inspect and clean it. There is a small port in the MC that is prone to clogging. You can use a single wire from a wire brush to clean it out. Rebuild kits are not too expensive.

What he said.

As the sun warms the brake lines and fluid, it expands and overflows back into the calipers and MC reservoir. If the little hole is blocked in the bottom of the reservoir (connecting the MC cylinder to the reservoir) the fluid has no where to go but into the MC and Caliper cylinders to push the pistons hard back to the stops (resulting in no lever travel and locked brakes) Did you try spinning the wheels as it is likely that they were locked on by the brakes as the fluid expanded to push the caliper pistons hard against the disc.

[DannyBoats]

Yes, when it's warm enough for the lever to lock, the brake caliper is also engaged. I have to bleed a small amount of fluid to even get the bike to move. I'll take it apart on my next day off and follow your advise. Thanks again!

[MAC10]

I am working on the same problem, and posted about it. When I got the reservoir off, and the o ring out, I founds lots of gunk and crystallized old brake fluid on the bottom of the master cylinder.
I carefully cleaned it, and am leaving it overnight to soak in clean fluid.

I found two holes entering the piston area from the bottom of the master cylinder. The one closest to the lever end is large and easy to clean.The one toward the brake line starts equal size to the first hole, but tapers to a pinhole. I think so anyway, but I am not sure, and the drawings are no help. Are there two holes, and is the front one the pinhole? It is much harder to clean.I suspect mine is full of crystallized fluid.

Are there any tips for unclogging it?

[d_hoffman]

drilling that pin hole larger?

Funny. I'm fighting the same thing on one of my master cylinders. Getting that pin hole cleaned out is a pain. What if I just drilled it out with the smallest drill bit I can find? Would that hurt - has anyone tried that? My guess is it might - otherwise Suzuki would have made it larger to begin with.

[MAC10]

RE: drilling that pin hole larger?

I thought of drilling it larger, but that would hurt the master cylinder's ability to build and hold pressure. The hole is tiny, to allow only a small and gradual release of pressure as the brake lever is released. I have never seen a bit that small, and i think it is built like that for an important reason.

I hope that a good soak in new fluid will soften up the crystals and allow easier removal. That has worked for me in removing caked and dried fluid from other areas.

Anyone have other ideas or tips?

[almarconi]

Take a single wire from a wire brush and clean out the hole. It's really not that difficult.

[MAC10]

Master cylinder cleaning tips and a minor mode

In order to reach the tiny relief hole in the bottom of the master cyinder, I had to soak it in clean fluid overnight to soften the gunk and old crystallized fluid.

The next challenge was to get the gunk out of the hole proper. I accomplished this by using a 5/64 drill bit by hand to get as far as I could without removing any metal. Lots of black gunk was got at this way.Then I very gently spun the drill under power, to counter sink the tiny hole, creating a beveled bottom with the pinhole in the center. Before I did this I could not get the very fine cleaning wire into the hole.There was just enough irregularity from corrosion to prevent it. After the countersink, it was easy.Remove only a very small amount of aluminum, just enough to create the bevel.

I had trouble until I found a wire small enough. The one I used measured.06 mm diameter. That is .00236 inches. It was a strand from some aircraft cable. My first attempts were way too big.

So far so good. it is assembled, filled and bled. I will leave the lever taped down and the handle bar turned so the master cylinder bore angles up toward the reservoir overnight,to get the last fine bubbles out, and will do the final bleed and test drive tomorrow.