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Rear brake issue 04 CRF250

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Peoples,

 

Having some rear brake issues, after a big ride the pads were getting down and lost some feel so decided to replace the pads and fluid. Changed the pads out and the. Bleed the old fluid out until all the new had worked it’s way through. But I couldn’t get the pedal to firm up at all and the piston won’t move. I re-bleed again to make sure I hadn’t sucked air in by accident, I then bleed backwards using a syringe, still nothing. I’ve now pulled the whole unit off in one piece and bleed on the bench with the MC below the caliper to make sure any air goes up. Still getting no movement or pedel feel. I could hear what sounded like air passing through the MC when I was manually depressing, I also did notice an air bubble appear. I wondering if the main cause could be the MC not producing enough pressure and also sucking air in? Or is it the caliper? Should I look at replacing the line also?

 

Cheers in advance for the help.

 

Warren

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If the caliper's piston is free to move in/out (not rusty, binding, cocked etc.)

and you're positive the air has been bled out, then most likely yes a bad master cylinder could be suspected.

 

Using the same technique a you, the MC positioned lower and caliper higher

while switching over to a steel braided line my front master would just not pump up

 

Only after doing the initial fill by gravity with the MC positioned higher (as mounted on the bike)

even with the caliper lower, only then was the fluid able to push out the majority of the trapped air.

Final bleeding done on the bench with the caliper held higher.

 

Also making sure you are using a spacer between the brake pads that simulates the approx. thickness of the brake rotor.

Edited by mlatour

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If the caliper's piston is free to move in/out (not rusty, binding, cocked etc.)
and you're positive the air has been bled out, then most likely yes a bad master cylinder could be suspected.
 
Using the same technique a you, the MC positioned lower and caliper higher
while switching over to a steel braided line my front master would just not pump up
 
Only after doing the initial fill by gravity with the MC positioned higher (as mounted on the bike)
even with the caliper lower, only then was the fluid able to push out the majority of the trapped air.
Final bleeding done on the bench with the caliper held higher.
 
Also making sure you are using a spacer between the brake pads that simulates the approx. thickness of the brake rotor.



Yeah I’m able to move the piston manually l, but get no movement at all when pumping the brake, I’ve let it hang for a while to make sure any trapped air is allowed to move up, failing that I think it’s a MC rebuild, which isn’t a massive thing, just didn’t want to go rebuilding things if I’m missing something first.

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