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rear brake not bleeding - rebuilt master cylinder (x-post from 2-stroke forum)

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My bike is a 2004 CR250 2-stroke..prety sure it shares the same brakes as the CRFs did that year.

 

 

Fluid is being pushed out of the rear master cylinder where the line attaches to it but when I put the line on, it doesnt want to push the fluid through the line.

 

I have a vacuum pump here and spent quite a bit of time trying to get the fluid to come through and it wont, at all. Even held the brake lever down too.

 

What am i doing wrong?? Has anyone else experienced this?

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I have played a similar game with the front brake master cylinder.on two bikes.  there was an air bubble in the cylinder where the plunger operates.  I heated it very gently with a heat gun and pushed the brake lever down and let it snap back sending shock waves through the system.  Eventually little bubbles came out and then all was good!

Edited by bikedad1

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I have played a similar game with the front brake master cylinder.on two bikes.  there was an air bubble in the cylinder where the plunger operates.  I heated it very gently with a heat gun and pushed the brake lever down and let it snap back sending shock waves through the system.  Eventually little bubbles came out and then all was good!

 

i will be trying this. thanks

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I'll cross my fingers for you, let me know if it works, and if not, what did.  So we are still left with 5 possibilites IMO

air in master cylinder

master cylinder needs rebuild (cheap and easy) 30 bucks

breakline bocked (not likely)

passeges in caliper body blocked

calipers frozen.

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Another way is to close off the bleeder screw and pump the lever 15-20 times to build a little pressure (likely just air pressure) and crack the bleeder immediately after and it should start moving some fliud, after doing this a few times then you can normally gravity bleed it without issue.

 

If not then there is a problem, normally if it pumps forever and never makes pressure you likely have a bad internal master cyl seal. But its a cheap easy fix

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Get the caliper above the master cylinder (by removing it)

Push the  caliper pistons all the way in with the line opened up then close it.

Put the caliper below the master cylinder (off the bike)

Vaccum pull fluid with a mitey vac

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thats the problem..it seems to move fluid once the line is off but when i hook the line up it wont move any fluid. guess something didnt work out...i bought it 'rebuilt' so maybe i got shafted.

 

darnnit

 

 

Another way is to close off the bleeder screw and pump the lever 15-20 times to build a little pressure (likely just air pressure) and crack the bleeder immediately after and it should start moving some fliud, after doing this a few times then you can normally gravity bleed it without issue.

 

If not then there is a problem, normally if it pumps forever and never makes pressure you likely have a bad internal master cyl seal. But its a cheap easy fix

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Still think you got an Air bubble in the master.  or even one of the rubber plunger type things inside is backwards?  I haven/t seen a rear one apart so not really sure what in thier.. but I figured with the front one I took apart It would be possible to have one sort of folded and not seal.  Easy to rebuild and cheap like S.F. .said.  Did you try some of the tricks here to get it pumping.  My votes air bubble!  Mostly because its nearly 0 effort to fix and 0 cost,  RUle that out and then start worring about the caliper assembly.  Did it ever work?  WHat prompted you to require it to be fixed?  Maybee we need a bit more detail as to what happened?

Edited by bikedad1

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