QuestionThis is a weird one! My nephew has a 1981 CM400 Custom. We rebuilt the front brake caliper, of course bleeding them properly afterwords. The new problem is after minimal to no pressure on the brake handle the front brake "drags". Not just a little, but continues to drag, more and more, until it stops the bike-sometimes so abruptly as to cause my nephew to come over the handlebars! (he's o.k., but broke up the headlight and turnsignals)Occasionally, he swears it brakes by itself! Neither of us can figure this out. All you need to do is squeeze the brake handle about 1/4" inch or less while rolling the bike forward and the brake just SLOWLY applies itself. I am stumped. I have been doing brakes for twenty years and never heard of such a thing. My local Honda dealers are scratching their heads in disbelief. Can you think of ANYTHING that would cause this? It's a lever, a cylinder, a line and a caliper! What could cause this? I patiently await your answer-Thank You!
AnswerPatrick, it sounds like the bleed port in the master cylinder is blocked, which holds pressure in the line. As this occurs, the pads heat up and expand, then grab the disc.
Rebuild the master cylinder, or at least clean it thoroughly. The bleed port is the tiny one where the bubbles are supposed to come out, located in the floor of the master cylinder towards the line end.
If you get the brake to apply, try opening the caliper bleeder and see if the pressure releases it again. If not, then you may have a caliper piston hanging up or some kind of alignment issue. Make sure the caliper is free to slide on its mounts, too.
If all seems okay at both ends, perhaps the brake line has collapsed internally.
Bill Silver
