Motorcycle Repair: 84 Honda CB900 brakes, honda cb900, caliper pistons

Question
Chris,

I am fixing to tear into my son-in-laws 900 the front disk brakes lock up tight.  He has changed the fluid, and changed the brake lines, I think it is the master cylinder, but have not opened one up  before, is there something to look for?  It seems to trap pressure in the system, a sunny day warms the master cylinder, then it locks up.   It has done it other times as well, sometimes it seems there is no reason.

Thanks,
Colby

Answer
Hi Colby.
 Well, there is only one thing to look for with this problem and that is anything blocking the return ports.    You shouldn't have any real problems with it as the master cylinder is a very basic assembly with few moving parts.
But I would be willing to bet that the problem is down in the calipers or in the T-connection in the line for the callipers.

 If the bike has dual front disc, which Hondas are known for, then make sure that it is both discs that are locking and not just one that is locking.  If the pad wear is uneven between the 2 calipers, then the problem is in the one caliper and not the master cylinder.  They could need to be rebuilt or just cleaned out properly.

Sometimes, the only thing needed to be done is to go in with a brass bristle detailing brush and some heavy cleaner and clean the grime off of the exposed portion of the caliper pistons.  Sometimes you need to disassemble the caliper completely and do a thorough cleaning of the calipers.

Good luck.
FALCON