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New Rear Master Cylinder not performing well

Discussion in 'Norton Commando Motorcycles (Classic)' started by p400, Apr 4, 2019.

  1. p400

    p400 VIP MEMBER

    Joined:
    Jul 14, 2014
    I purchased a new stainless rear master barrel assembly from Bonnevilleshop and have installed it , tried to bleed the rear caliper, but this master did not seem to be pumping.

    Removed new rear master, filled with fluid, attemping to pump, but it only pushes a inch or so of fluid when compressed, but sucks it back in when released.....when hooked up as shown.

    There is about .005 - .010 clearance from this new stainless barrel and the pushrod.

    Is a preload needed to achieve correct pumping?

    20190404_Rearmaster.jpg
     
    Last edited: Apr 4, 2019
  2. p400

    p400 VIP MEMBER

    Joined:
    Jul 14, 2014
    So reading further - I have screwed the new barrel in one turn to preload and seem to get the same result of pump small amount out but suck it all back in .

    I cannot get another barrel turn to achieve more preload.
     
  3. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Joined:
    Nov 20, 2004
    Have you tried restricting the return flow?


    Correct procedure is to screw the barrel assembly inwards until all pushrod play has just been removed.
    The barrel should then be given one full turn plus whatever part of a turn it takes to bring the reservoir stud back to the vertical position at which point it should be possible to blow air back through the unit from the outlet to the reservior vent hole.

    http://www.classicbike.biz/Triumph/.../Lockheed_Hydraulic_Brakes_Triumph_Norton.pdf
     
    p400 likes this.
  4. p400

    p400 VIP MEMBER

    Joined:
    Jul 14, 2014
    This Mk3 rear assembly, and I am sure any other mk3 would be same, has the push rod making contact and allowing 3/4 turn to complete the reservoir back to upright and no more turns allowed due to mechanical lock up of the push rod within the black cast housing.

    Is the only test to confirm that fluid and air will return to the reservoir when at rest ?

    RearMasterTest1.jpg
     
  5. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Joined:
    Nov 20, 2004
    The pushrod shouldn't completely lock up and prevent the barrel assembly from being screwed further in, if that's what you meant, or the pushrod wouldn't activate the piston.
    If you mean the pushrod then starts to press against the piston as you screw the barrel assembly into the casting then that sounds normal.

    It's a check that can be done before reinstalling the master cylinder. It doesn't actually need a pump but it's probably healthier than physically blowing through the unit once it is contaminated with brake fluid and it doesn't need to have fluid in the reservior.

    An alternative would be to check if the caliper pistons push back into the caliper relatively easily but the system needs to be connected and bled for that.
     
    Last edited: Apr 4, 2019
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  6. p400

    p400 VIP MEMBER

    Joined:
    Jul 14, 2014
    I was able to bleed the system with this additional 3/4 preload turn.
    1/4 turn until no push rod clearance and then 3/4 to complete a full turn,
    brake works okay , but too much rear brake pedal stroke required.

    i believe that i cant get another barrel turn because of running out of clean threads.
    So i can think of three options-
    1. take apart and clean threads in the cast housing to allow another turn.
    2. grind the first thread off the new barrel.
    3. add a spacer to the push rod.
     
  7. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Joined:
    Nov 20, 2004
    That would be the logical (sensible) course of action, in my opinion.
     

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