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Front break problems help please

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2003sporty

New Member
I have a 03 Sportster 883xlh, it has a 9/16 master cylinder with an aftermarket 4 piston caliper, and steel braided line. Ive changed all of the seals in the caliper and I cant see anything wrong with the seals in the master cylinder. I have fluid coming out of the bleeder valve (dot 5) but the only way I can build pressure is to pump the lever quickly and it will hold pressure as long as you do not let the lever go, if you do let the lever go after a few seconds it will go all the way to the handle bar. I have tighten every point that can be tighten to ensure the system is sealed and there are no leaks anywhere at this time - any suggestions?
 
I would suspect from your description of the problem that the master cylinder seals have failed
The seals on the piston in the master cylinder should hold firm when pressure is applied to the brake leaver and fold when released allowing more fluid into the system and hold it there when the piston is not moving
A master cylinder rebuild kit is what you need the new piston in the kit will have the seals fitted on it and they are not replaceable

Brian
 
I second that the seals in the master are letting the fluid bypass and the reason why loosing pressure.....
 
2003sporty said:
I just rebuilt the master cylinder and the symptoms did not change.....
Click to expand...

Take the cover off the master, pump the brakes do you see the bubbles coming out of the compensator port in the master?
Keep in mind even with a rebuild kit yor master still may have a bad or plugged compensator port or the seals have already rolled over
 
Is it possible that the master is too small to apply proper pressure for a 4 piston setup?
 
When pumped with the cover off I can see fluid squirting out of one of the ports - the fluid is to dark to tell which one bit appears to be coming from the one closest to the leaver
 
I'm not totally clear on what your symptoms are, but I think you still have air in the line. It can be a rather tedious process to get them bled completely. Additionally, if the fluid is that dark, it is time to change the fluid. Also, IIRC the factory single disc setup used a 5/8" bore master cylinder, and the dual disc ran a 9/16" bore master cylinder.
 
Looking at Tucker Rocky's catalog the '960'03 XL's use a 9/16 bore for single disc, and 11/16 bore for dual disc. 5/8 bore was from '84-'95 XL's.
I would agree with with more bleeding or something is in wrong in the MC
tourbox
 
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