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problem bleeding rear brakes on Sportster

rgooch

New Member
I rebuilt the master cylinder. I'm unable to get the brakes bled. Using a vacuum pump its not working. Emptied the reservior three times and still sucking air. Brake paddle still soft. Cylinder on caliper is pushing out with no presser. Pedal falls to the floor. No brake light.
 
It has been my experience that the only way to reliably get that master cylinder bled is to open the bleeder screw, push the pedal down, and close the bleeder with the pedal depressed. Release the pedal, open the bleeder, depress the pedal, close the bleeder.....you get the picture. It is a slow, tedious process, but it will work.
 
Possible something is a miss with master and fluid is bypassing one of the seals....:(
Can master be removed and tried to be bench bleed?
 
Sound like the master rebuild isn't quite right. May need to take it apart and inspect it carefully.
 
Sound like the master rebuild isn't quite right. May need to take it apart and inspect it carefully.

I'll second that motion. Common problem is a nick in the piston oring/seal, or a bit of rubber in the return port.
 
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Also with the cover off pump the brakes do you see bubbles coming out of the compensator port in the bottom of the cylinder? If you do not either rebuild again and clean the port or replace the master
 
I tore apart the master cylinder in found the primary Cup was torn I was real careful when installing how can I be more careful
 
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