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Discussion Starter · #1 ·
I can't figure this one out.

I replaced my front master cylinder because the old one was acting odd (the handle seemed like it was stiffening up after I hit the brakes hard.)

I bled the brakes at the cylinder and both front brake calipers. After riding about 40 yards, the following happened:

  • Front calipers locked up
  • Brake handle is so stiff I can't squeeze it at all.
  • Brake light comes on.
  • Pressure can be released by opening the bleed valve at the front right caliper.
I used DOT 5.1 fluid and filled the reservoir below the max fill line. For the life of me, I can't figure this one out. All signs would point to a faulty master cylinder, but the one I bought is an OEM part brand new.
 

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790R, KLX350, Canyon Enduracer, Santa Cruz
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133 Posts
I would closely inspect the pad/rotors for clearances once it locks up. Something is getting stuck or h2o got in the brake fluid and it all needs to be replaced.
 

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Sounds like you need to take out the pistons, clean them out, and put new seals in. I had a 900 Trophy in the UK (lots of winter salt on the roads) and it needed doing every couple of years due to the calipers corroding, and the brakes would start binding and locking up if it wasn't done
 

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2008 RC8 / 2007 690
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7,332 Posts
I bled the brakes at the cylinder and both front brake calipers. After riding about 40 yards, the following happened:
i suggest reseting the front brake lever so the pushrod is loose and the lever isnt acting on it.then test again.
 

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Discussion Starter · #8 ·
Figured it out. It was the front brake lever that was slightly actuating the master cylinder, therefore not allowing the fluid back into the reservoir when the brakes heat up.

I bought the bike used and it had an aftermarket brake lever. When I replaced the master cylinder, this happened. It turns out the previous owner had shaved down the master cylinder actuation pin to make it work with the aftermarket handle.

When I put the factory handle back on, it worked perfectly. This was maddening, but we figured it out. Thanks for all of the help.
 
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