Sticky rear brake
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Sticky rear brake
Hi all,
I recently changed my rear brake master cylinder on my '78 FLH as the old one was duff. Before I put it on the bike I took it apart and checked it over. The cylinder moved smoothly all the way in and out and all seals and the spring looked fine.
However, once it was on the bike and I had taken all the air out of the system, the brakes go on well, but then don't release enough for the pads to clear the disc completely. The friction then heats up the whole caliper including the brake fluid whilst riding and closes the pads onto the disc. This goes on for a mile or two until the whole thing seizes up and I have to release brake fluid from the caliper to get going again.
Questions:
- by what mechanism are the pads supposed to move away from the disc (completely) and where does the brake fluid go in that case? Back in to the MC?
- If so, could it be that the cylinder in the brake MC doesn't move back enough for the brake fluid to flow back in to the MC after braking?
- what else can it be; duff caliper? It was professionally cleaned before I put the new MC on....
Appreciate any pointers.
Cheers
Paul
I recently changed my rear brake master cylinder on my '78 FLH as the old one was duff. Before I put it on the bike I took it apart and checked it over. The cylinder moved smoothly all the way in and out and all seals and the spring looked fine.
However, once it was on the bike and I had taken all the air out of the system, the brakes go on well, but then don't release enough for the pads to clear the disc completely. The friction then heats up the whole caliper including the brake fluid whilst riding and closes the pads onto the disc. This goes on for a mile or two until the whole thing seizes up and I have to release brake fluid from the caliper to get going again.
Questions:
- by what mechanism are the pads supposed to move away from the disc (completely) and where does the brake fluid go in that case? Back in to the MC?
- If so, could it be that the cylinder in the brake MC doesn't move back enough for the brake fluid to flow back in to the MC after braking?
- what else can it be; duff caliper? It was professionally cleaned before I put the new MC on....
Appreciate any pointers.
Cheers
Paul
Last edited by McBoney; Sep 6, 2011 at 03:40 PM.
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Update;
I have found the problem.
Because the push-pin linked to the pedal was too long, the cylinder in the Master Cylinder was not retracting all the way back after braking, thus blocking the fluid return into the MC. That kept the pressure in the caliper, which heated the fluid, which pushed the pads further against the disc etc etc.
Apparently the pin needs to have 1mm play to the cylinder when the pedal is not depressed. That allows the cylinder to fully return and opens the fluid return enabling the pads to fully retract from the disc.
Easy fix (for once!)!
Cheers
Paul
I have found the problem.
Because the push-pin linked to the pedal was too long, the cylinder in the Master Cylinder was not retracting all the way back after braking, thus blocking the fluid return into the MC. That kept the pressure in the caliper, which heated the fluid, which pushed the pads further against the disc etc etc.
Apparently the pin needs to have 1mm play to the cylinder when the pedal is not depressed. That allows the cylinder to fully return and opens the fluid return enabling the pads to fully retract from the disc.
Easy fix (for once!)!
Cheers
Paul
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