Rear brake stuck.

Discussion in 'Mechanics Garage' started by Mariusz, Apr 13, 2019.

  1. Mariusz

    Mariusz New Member

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    Hi have a problem with me vfr 800 vtec 2002 rear brake is stuck and dont move... to be exact middle piston dont move. I take caliper apart clean it and bleed etc. Had piston moving nice and smooth but when everythink put together just press the brake and its geting stuck again its just not going back. Any ideas whats wrong? Do day gave some valv or pressure switch on abs or what can be the problem. Thanks for all the help

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  2. OOTV

    OOTV Member

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    The rear caliper center piston is controlled by the Secondary Master Cylinder, that’s the gizmo that is attached to the front left caliper. The way it is designed to work is that when the front wheel is rotating forward and the front brake is used, the caliper will squeeze the rotor and the rotational force will cause the SMC assembly will pivot forward and trigger the actual SMC. This in turn sends brake fluid to the rear center piston, it will go through a proportional valve first though.

    This is the simplified version as the ABS model I believe has two rear proportional valves. If you feel like tackling the brakes yourself, go to www.vfrdiscussion.com and down load the Honda Factory Service Manual from the downloads section. Sounds like the rear lines might need to be flushed and bled.
     
  3. fink

    fink Insider

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    Have just answered the almost exact same question on a Cbr forum. as per wot OOTV says.
     
  4. Terry Smith

    Terry Smith Member

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    So the short version is, there is some crud in the secondary master cylinder that needs to be cleaned out. All master cylinders have a tiny return port (most easily seen in the front brake, in the reservoir under the small metal cover on the floor) that allows pressure to release from the line after application. If that port gets clogged, the pressure doesn't release and you have a piston that can't retract.
     
  5. Mariusz

    Mariusz New Member

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    Thanks for all the help. It was smc stuck on small port ti try to flush it clean it and after small help of the compressor i get it out. Now is all working fine

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