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Old 02-04-2018
dieseldude dieseldude is offline
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01 WR250 rear brakes

I keep going through rear master cylinder reservoirs due to the heat from the exhaust distorting the plastic canister.

I bought an aftermarket later model rear master cylinder off Ebay and have tried a few times to get it to work.

Is there a trick to bleeding these units?

I've used a large syringe to reverse bleed the system from the caliper up, but it doesn't work. There's no pedal feel either way. If I bleed the system by pushing the pedal down and cracking the nut, fluid dribbles out, but nothing happens as a result.

On the bench, the master cylinder appears to work. With a full reservoir and fluid in the chamber that moves via the piston / pedal being moved, fluid looks to move about. When fitted to the bike though, the full stroke of the pedal has little resistance and the piston on the caliper barely moves........

There are 2 allen key screws in the lower rear side of the master cylinder. Do these come into play when bleeding the system?

Cheers.
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Old 02-04-2018
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Pygmygod Pygmygod is online now
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Dunno about the 01 or the aftermarket one, but on mine I had to do the vacuum bleed method via a large vet syringe to pull a vacuum, then crack the bleed nipple and it forced a bunch of air out which normal bleeding didn't remove.
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Old 02-04-2018
dieseldude dieseldude is offline
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Quote:
Originally Posted by Pygmygod View Post
Dunno about the 01 or the aftermarket one, but on mine I had to do the vacuum bleed method via a large vet syringe to pull a vacuum, then crack the bleed nipple and it forced a bunch of air out which normal bleeding didn't remove.
Maybe I should by trying to pull the fluid through rather than pushing it in via the bleed nipple. Is this what you're saying you had to do? I reckon it would just suck air in from the bleed nipple doing it this way though............

It's a bastard of a thing.
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Old 02-04-2018
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Pygmygod Pygmygod is online now
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I tried pushing it up, I couldn't get it to build pressure either.

Read this thread:
http://www.dirtbikeworld.net/forum/s...=123075&page=2

The theory is the same as these:
https://www.youtube.com/watch?v=PwAQ2qDQjPg

Just by using the large syringe to pull a vacuum instead of that mityvac hand pump thing he's using.
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