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Brake headache solved PSA!

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I want to share this so others won't do the same thing.  I spent quite a few hours troubleshooting a rear brake problem. It was painful.  It did not matter how I bled them I could not get pressure out of the rear brake on my WR 450.  

I will spare the gory details but I rebuilt my master cylinder twice and rear caliper threee times (I used rebuilt kits).  I swapped high calipers and hoses off my 125.  No dice. In the end I emerged victorious!  The culprit was a scratched piston!  I took an extra close look at the piston on the last round.  You could not really feel any ridges on it (DOT 4 fluid is slick) easily  but if you looked close enough and ran your thumbnail over it, you could feel them.  I polished it with 2000 grit paper, put it back together one last time and achieved pressure is a few pumps.

When rebuilding brakes it is best to do both the master cylinder and caliper.  Blow all fluid out of the line and polish that piston.  Do this and you will not have to chase your tail like I did!

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