Rear Master Cylinder Pressure
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  1. #1
    Noob! JohnnieBoy's Avatar
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    Rear Master Cylinder Pressure

    I have rebuilt my rear master cylinder with new banjo bolts, washers, seal kit, connector kit. I have rebuilt the rear calipers with new pistons, seals, banjo bolts, and nipple.

    I cannot build pressure. I took everything apart again, and all the lines were clear and installed properly. All seals are installed properly. The 2 holes on the master cylinder that connect to the reservoir are clear. I have tried various adjustments with brake lever height.
    I tried a combination of bleeding from master cylinder banjo bolt, caliper banjo bolt, and nipple; nothing draws the fluid.

    When I remove the banjo bolt from master cylinder and press on brake foot lever, the fluid rises then immediately falls as I release foot lever. Is the fluid supposed to fall again? Shouldn't it only go in one direction? How would pressure build?

    My next move is to reverse bleed by pushing fluid up from the caliper nipple with a syringe, but I don't want to waste my time if master cylinder isn't functioning properly.

    Thank you for suggestions.

    John
    Last edited by JohnnieBoy; 10-07-2018 at 07:08 AM.

  2. #2
    Noob! brittrip's Avatar
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    Hi John, Had the same scenario when changing from 14mm to 12mm rear master on the cripple, changed to a pressure switch in the banjo at same time,didn't want to bleed down, pressure bleeder from caliper back did the trick, get the same with most truck air/hydraulic clutches, pushes air back to reservoir and jobs a goodun,

    hope this helps, Calvin.

  3. #3
    Noob! JohnnieBoy's Avatar
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    Thank you; however, I just tried a reverse bleed and still no success. I pushed fluid from the caliper all the way to the reservoir. The caliper is still loose on the disc and the pistons have not engaged.
    I think the problem is because the fluid in the master cylinder is flowing both ways, hence no pressure can be established?

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  5. #4
    Noob! brittrip's Avatar
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    You will always get a small amount of fluid going back to the reservoir before it decides to do its job, that's how the pressure in the line is relieved when the brake is released, if the reverse bleed did not work,you may still have air in the line depending on how your brake lines run,you can remove the master again, move it up and make sure the pipe has an uphill path to the cylinder itself from the caliper then no air can get trapped,usually either side of the dip by the swing arm, take the pipe off the reservoir and put it into something a little larger you can push thru a goodly amount then without keep stopping, its very often air in the pipe work that pushes the fluid back and the compression of a volume of air by a gnats piss that the cylinder delivers doesn't make the game easy
    Last edited by brittrip; 10-08-2018 at 12:33 AM.

  6. #5
    Noob! Se Sua's Avatar
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    Quote Originally Posted by JohnnieBoy View Post
    Thank you; however, I just tried a reverse bleed and still no success. I pushed fluid from the caliper all the way to the reservoir. The caliper is still loose on the disc and the pistons have not engaged.
    I think the problem is because the fluid in the master cylinder is flowing both ways, hence no pressure can be established?
    Hi I've had the same... But taking the caliper off and keep the bleed screw in the highest position (of the complete line) and try again. This works with me every time. I don't even try to bleed it when it still is mounted on 'swingarm'.

 

 

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