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Discussion Starter · #1 ·
After my last ride a few days ago, I reached down to feel my rotor and it was burning hot. Took the caliper off and noticed that the caliper piston dust cover was either worn or burned through. Got another one ($20.30!) and put it on today. In addition, I drained the system and ran everything through the ultrasonic cleaner. Rinsed and dried, I reassembled the system and bled the brake. Spun the front wheel and noted a great deal of drag. For what it's worth, I have a new USA Motorcycle Master Cylinder, a new braided brake line, a new caliper seal, and fairly new pads. Obviously the piston is not releasing properly. Any ideas?
 

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When you had the caliper off, did you also remove the piston seal and completely clean out the sealing groove with a dental pick or other object. I would doubt that a sonic cleaner would touch that stuff that builds up in there. And a clean groove is important to the retraction of the piston. I assume you lubed the sliding pins in the caliper so that it can "float" on the mount.
 

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Discussion Starter · #3 ·
When you had the caliper off, did you also remove the piston seal and completely clean out the sealing groove with a dental pick or other object. I would doubt that a sonic cleaner would touch that stuff that builds up in there. And a clean groove is important to the retraction of the piston. I assume you lubed the sliding pins in the caliper so that it can "float" on the mount.
I did clean the groove well. Surprisingly little was there. And yes, I also cleaned and re-lubed the sliding pins. Frustrating situation.
 

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Discussion Starter · #4 ·
I did clean the groove well. Surprisingly little was there. And yes, I also cleaned and re-lubed the sliding pins. Frustrating situation.
Going to polish the piston to mirror quality...there has to be a source of drag and I'm guessing this could be it.
 

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Bryan, common source of the issue is clogged return hole in the MC. I'd check that next (actually first, but it's a bit late for that now lol
)
 

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With a new MC, I would assume the return hole to be clear, but who knows? Have you tried forcing fluid back up to the MC, using a syringe on the bleeder screw? That would show if the return hole was clear. Other than that, I'm not sure what could be causing the problem. The only thing left is a pinched line, and you said they were new too. You might swap back to the old line temporarily and see it that helps.



I know Rickbert had a problem with his MC from USA, but it wouldn't develop any pressure. Maybe a quality control issue.
 

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Discussion Starter · #8 ·
Just a thought, how's your rotor?
Interesting thought about the rotor. Prior to rebuilding the caliper I did notice a "spot" in which the brake would grab a bit harder. To counter that I loosened and re-torqued the rotor bolts which seemed to correct most of the issue. It would seem very possible that the heat generated by the rubbing could have warped it enough that it could affect the brakes. I will try to check it for true.
 
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