Expert: (Sidecar) Bob Kingsmill - 3/22/2009

Question
The more i drive this bike the more the brakes stick? That's with in a Hours time it actually gets to the point if i stop i cant get going. If i let the bike sit over night its fine the next day, I haven't had the bike that long and its my first bike. I hope you can give me some idea of whats going on.

Answer
When the brakes lock up without any lever application it is usually caused by a blocked return port in the bottom of the master cylinder.

If you look in the bottom of the master cylinder you will see two holes drilled about 1/8" into the metal. In the bottoms of those holes you should see tiny holes that go right through to the bore that the m/c piston moves in. One admits fluid into the cylinder so that it can be pumped into the brake line when you squeeze the lever. The other one allows the fluid to return to the reservoir when the lever is released.

For some reason, the one that lets the fluid return tends to become blocked. In some cases it will look like the tiny hole was never drilled.

The proper solution is to disassemble the master cylinder and use a sewing needle to clear the hole. It is possible to clear the hole without dismantling, but that will leave the hard piece of debris in the bore and it can lead to a scratched bore, a scratched (& therefore leaking) rubber cup or both, so it is not advisable.

While you already have the master cylinder apart it would probably be agood idea to put a rebuild kit into it (unless you know absolutely for sure that it has ben done in the last few years). 25+ years in brake fluid is a long time, even for rubbers that were designed for it. Even if your master cylinder seems to be working properly, it wouldn't hurt to replace rubber parts that old.

NOTE: You didn't say what year your 1100 is. If it is an '83, you have linked brakes - one of the front calipers is operated by the front master cylinder and the other one is operated by the rear master cylinder. If the problem is in one of the front calipers make sure you are working on the correct master cylinder.