QuestionQUESTION: Hi, thanks for your help.
I've rebuilt the (front) master cylinder on my '77 CB 550, but now can't get the brakes to bleed. An hour and a half of the pump-and-hold method only pushed six inches of fluid into my bleed tube, and I feel no pressure at all on the brake handle. Tried the hand-pump vacum without any better luck. The two holes in the bottom of the resivoir are clear, and I bench-bled the master.
A couple things: the bike sat all winter.
The brake piston is extended to, and the pad is flush against, the rotor. Could it be frozen? If so, would that cause my problem?
I'm having trouble opening the bleed valve enough to allow fluid to pass without opening it so much that fluid seems out. (Realize this isn't good for keeping air out, but not sure it would cause the problem I'm having.)
I'm thinking of taking the whole system apart and bench-bleeding each section as I put it back together. What do you think?
Thanks again for your help.
ANSWER: Tyler, the brake piston isn't the problem. If the system was building pressure, the brake would firm right up even if the piston was seized in the caliper. When you put the vacuum pump on it did it draw fluid out of the upper reservoir? You need to have a pretty good flow through the system to get all the air out. Assuming you got the parts back into the master cylinder the way they should be, it has to be air trapped in the system. If you happen to put the cup in the master cylinder backwards, it never will build pressure.
Regards
Rich
---------- FOLLOW-UP ----------
QUESTION: Thanks a lot, Rich.
A vacuum on the master cylinder itself did draw fluid from the reservoir, but a vacuum on the bleeder bolt didn't do anything. I don't know, but it seems to me that a vacuum on the bleeder will draw fluid unless there's a blockage somewhere. Is that right?
It's certainly possible that I put the master back together incorrectly, but I'm reluctant to take it apart again unless you really think that's the problem because of how hard it is to get that internal circlip out. (I broke the last one.)
Otherwise, I'm going to try to bench-bleed again and maybe check the hoses individually to make sure they're flowing. Any other ideas for getting trapped air out?
Thanks again.
AnswerTyler, it sounds like the bleeder screw is plugged up or the brake lines have swelled up internally and are constricting the flow. You should be able to draw fluid from the reservoir down to the slave cylinder by putting the vacuum line on the bleeder screw.
Try blowing compressed air through each of the lines to make sure they are clear.
Yea, that snap ring is a pain, check that olny after everything else checks out.
Regards
Rich
