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Thread: Dem bleedin' brakes

  1. #1
    Atomic City Boxer 154048's Avatar
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    Dem bleedin' brakes

    My rear Brembo worked pretty well, but as a PM, I replaced the hydraulic hose.

    With the new hose on, I set out to bleed the fluid from the line. I have done this many times on autos, but here, I pump and pump and don't seem to get 'solid pedal'.
    The reservoir is full of fresh DOT3, and I am getting a spurt out each bleed, but the pedal never seems to pump up to solid, even after a dozen or more pumps.

    What am I missing?

    Thanks
    Steve in Santa Fe
    1980 R100RT
    96' Triumph Trophy

  2. #2
    Make sure all the fittings are tight and the bleeder valve is at the highest point possible, maybe try bleeding the line first then the caliper?
    "Wow I didn't know BMW made motorcycles, Yeah I think Honda does too."

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    Registered User Anyname's Avatar
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  4. #4
    ABC,AMA(LIFE),MOA,RA,IBMW MANICMECHANIC's Avatar
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    If memory serves, the rear master cylinder is on the right side, and the brake line crosses over the top of the swing arm, then goes down and back to the caliper. So you have the potential for a large bubble in the crossover. What works is to have somebody hold the caliper up higher than the master cylinder, and possibly upside-down while bleeding to help force the bubble to the highest point.
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  5. #5
    This winter, for SuperTech, we sectioned open a Brembo caliper so folks could see where the fluid passages were and where air can get trapped. We learned that it's way too easy to trap air in the caliber and, on the early Brembos, you may not be able to flush the air out from behind the pistons with standard bleeding. Since you've opened the system to change the line you really need to be sure the caliper is full of only fluid before you reassemble it to the hose (oh, I wish you could see the cut-away. No, I don't have photos). Any air behind the piston, between it and the caliper body, could be trapped like air in a Pepsi bottle - only one opening at the top and no matter how hard you flush fluid past that one opening you cannot sweep the air out.

    I've not seen your caliper but I'll bet the bleed screw is in a port that is right at the end of one of the ribs that run up the outside of the caliper. The fluid passage from the hose runs past the opening for each piston and up that rib to the bleed screw. Dismount the caliper and orient it so that the junction of that rib and the cylindrical part of the caliper casting is a high point, then keep bleeding. You may also have some luck with leaving it that way over night and the air bubbles migrating to the bleed screw by themselves. You may need to take that caliper back off and manually fill it and pump the air out then start over.

  6. #6
    It often takes more than a dozen pumps, sometime way more, to clear a system of all air after draining the entire system. You can try pumping fluid with a syringe into the bleeder (be sure to empty the reservoir first). Try gently tapping along the whole system with a hammer to loosen air bubbles. Remember that air will rise to the highest point and look at the M/C and caliper to see if repositioning them will help. If all else fails, make sure the path from the reservoir to the M/C is clear. I once had a clog just below the reservoir that took (too long a time for me to admit) to diagnose.
    '61 Clubman's Gold Star, '13 690 Duke, '13 Daytona 675R, '14 Street Triple R (gone but not forgotten: '76 R75/6, '84 R100, '76 R90S)

  7. #7
    It is frequently necessary when bleeding the rear caliper to remove it so the bleeder faces up. It also helps to get the caliper lower than the master cylinder.

  8. #8
    Atomic City Boxer 154048's Avatar
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    Been meaning to reply for quite sometime. Thanks to all who offered advise. Bleeding the rear Brembo is a royal pain. What finally did it was; starting at the reservoir, I bled each componant separately, then quickly reassembled.

    What finally did the trick with the rear caliper was to use a 30cc syring to force brake fluid backwards from the bleed port (while rotating and shaking the caliper...sheeesh). But I am back in brakeland. Just in time for a full weekend of riding.
    Steve in Santa Fe
    1980 R100RT
    96' Triumph Trophy

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