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Caution on rebuilding Master Cylinders

J

Jack Klarich

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Under NO circumstances should you hone an Aluminum master cylinder or use any abrasive on the pistons. These have an anodized finish on them and the scratching will ruin the finish and cause leaks. Best to clean all parts in alcohol and flush with hot soapy water, air dry and use quality Assembly fluid with new seals for reassembly.
 
Hey guys,
I have a 2005 sportster 1200C with brake problems. I recently rebuilt the rear brake master cylinder, changed pads and rebuilt caliper. The problem is that after a while the rear brake would be too pressurized and lock up. I think it has something to do with adjusting the master cylinder. Ay ideas?
 
jonathanhahka said:
Hey guys,
I have a 2005 sportster 1200C with brake problems. I recently rebuilt the rear brake master cylinder, changed pads and rebuilt caliper. The problem is that after a while the rear brake would be too pressurized and lock up. I think it has something to do with adjusting the master cylinder. Ay ideas?
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Did you change the adjustment on the rod? If so you will need a bit of free travel
 
I basically kept it the same. I don't remember how much, but the instructions said it needed to have a certain distance from the end of the rod to the nut. Do you have the instructions? I can't find mine.
 
jonathanhahka said:
I basically kept it the same. I don't remember how much, but the instructions said it needed to have a certain distance from the end of the rod to the nut. Do you have the instructions? I can't find mine.
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Jack up the rear wheel, pump the brakes til they lock up and will not release, back off the adjustment 1 turn at a time counting or marking your original spot, do the brakes release? If not the master cylinder is probably bad and will need to be replaced, you can verify this by pumping the brakes up and cracking the bleeder at the caliper, it should be squirting out under pressue
 
Thanks, Jack! I will try that. Just to be sure (new to Harleys) the adjustment screw is on the master cylinder closest to the pedal attachment on the end of the pushrod, right?
 
Did you use the correct brake fluid ? Dot 3 has a lower boiling point than 4 or 5. Also any moisture in the system lowers the boiling point.
 
I used dot 5, new bottle. after 10 minutes of riding, the brakes slowly lock until I stop the bike and release pressure by opening the line on the caliper. I am thinking since I rebuilt the master cylinder the return line is clogged/blocked. Ideas?
 
jonathanhahka said:
I used dot 5, new bottle. after 10 minutes of riding, the brakes slowly lock until I stop the bike and release pressure by opening the line on the caliper. I am thinking since I rebuilt the master cylinder the return line is clogged/blocked. Ideas?
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The return line? That would be the compensator port in the master cylinder, if this problem persists you will need to replace the master cylinder, as the rebuild did not solve the original problem
 
Ok, the compensator port. That was the problem. Just to make sure it was the CP, I removed the MC, took it apart and looked at the CP and the smaller hole was blocked. I tried to clear it the best I could and put it back together and on the bike. Problem was gone. I DO NOT RECOMMEND DOING THIS FOR A QUICK FIX, GO BUY A NEW MASTER CYLINDER AND STAY ALIVE!!!:rr
 
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