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  1. #1
    CB750 Addict Chris in Dorset England's Avatar
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    Bleeding the twin piston, twin caliper front brakes. CB750 F 1983.

    Having reached the stage in my rebuild of fitting the front brakes I ran into problems bleeding the air out. Rebuilt calipers, new pads and new braided brake lines. Following the manual(s) resulted in a very soft brake lever, several attempts at bleeding produced no improvement, the lever almost reaching the grip. Not good. Time for a rethink. Clearly there was still air in the system, how to get it out? Then I remembered that there was an Allen headed bolt on the underside of the calipers with a small hole connecting the twin bores together. This bolt is not mentioned in any of the manuals, which is less than useful. I took the calipers off, one at a time, used a piece of wood between the pads to stop the pistons coming out. Lifted the caliper as high as the line would allow with the bolt uppermost. Cracked off the bolt 1/2 turn and gently squeezed the brake lever, result, lots of air bubbled out! Closed the bolt, released the lever, and repeated. Refit caliper. This on the other caliper as well. Result, a good solid brake lever. I can only assume the Allen bolt is a secondary bleed point. None of this is mentioned anywhere in the manuals. Hope this helps someone with the same problem.

  2. #2
    CB750 Addict pidjones's Avatar
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    Good info. I'll be fitting '82 twin calipers to my '79 (with '82 C forks). IF I can get it all to fit up, bleeding is never fun for me. Any hints help (like priming the master before hooking it up to the system).


    Brakes are never fun for me.
    "Love 'em all.... Let GOD sort 'em out!"

  3. #3
    CB750 Addict Chris in Dorset England's Avatar
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    Quote Originally Posted by pidjones View Post
    Good info. I'll be fitting '82 twin calipers to my '79 (with '82 C forks). IF I can get it all to fit up, bleeding is never fun for me. Any hints help (like priming the master before hooking it up to the system).



    Brakes are never fun for me.
    Hi, Initially follow the manuals and see what happens. Bleed the left side 1st as it is slightly longer due to the cross over pipe.
    Fill the master cylinder with the handle bar to the left (keeps the reservoir level). If doing it by the manual does not give you a solid lever, not soft or spongey then try my system. The reason for holding the calipers high is to encourage the air bubbles to rise up ( as the gas in beer!) You may need a friend to pump the lever if you don't have 3 hands. The routine is the same. GENTLY squeeze the lever, crack off the bolt 1/2 turn, there is no way of fitting a tube, air should bubble out, close the bolt, release the lever and repeat until no bubbles appear. same on other caliper. Some things to remember: Keep the cap on the reservoir whilst squeezing the lever, or you will have fluid squirting everywhere, a piece of wood between the pads, to stop the pistons coming out and keep an eye on the fluid level on in the reservoir, too low and air will be sucked through the fluid rather like the bath emptying through the plug hole. DO NOT reuse old fluid, fresh fluid from a sealed container only.

  4. #4
    CB750 Addict pidjones's Avatar
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    A trick I've read about for new lines/calipers, etc. Is to fill as best you can, pull most of the fluid from the reservoir, then press the pads and pistons in to drive fluid (and trapped air in calipers/lines/crossover back intothe reservouir. Watch the level carefully and don't let it overflow or go low as you now pump the pads back out.
    "Love 'em all.... Let GOD sort 'em out!"

  5. #5
    CB750 Addict Chris in Dorset England's Avatar
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    Thanks. Worth remembering.

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