Rear Brake Bleeding

Discussion in 'Airheads' started by mikejet, Oct 2, 2012.

  1. mikejet

    mikejet KlrKid

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    Any trick to getting all the air out of the rear brake caliper on a R100S? Pedal is still a little soft. Rebuilt the cylinder - pads are good. I took the whole unit apart and it seems to me that the way its constructed, even using a pump - ( which I did ) - will not get all the air out. Maybe removing it from the rear wheel and turning it upside down while bleeding? Maybe pumping fluid up from the caliper into the master cylinder? Any thoughts would be appreciated. Not a good feeling riding with a soft rear brake !!!!
    #1
  2. pbarmy

    pbarmy Long timer

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    Havent done mine yet,but they say hang it upside down,this places the bleeder at the bottom,allowing all air to escape.Guess I'll try it this winter on my newly nekkid 79R100R/T.:evil
    #2
  3. bmwrench

    bmwrench Long timer

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    Remove the caliper and it's mount and hang it as high as possible. Bleed 'conventionally' by pumping the pedal and opening the bleeder. Make sure your linkage is adjusted correctly.
    #3
  4. DaveBall

    DaveBall Long timer

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    I have found that the easiest way to ensure no air in the system is to reverse bleed them. It can be done in place.
    Get yourself 2 large syringes from any pharmacy and some flex tubing that will fit the syringe and the bleed nipple. Use 1 syringe to remove the fluid from the resevoir. Fill the other syringe and tube with new brake fluid (suck it up). Attach the tube to the bleed nipple and loosen the nipple. Then slowly force fluid thru the system and fill the resevoir. I usually will empty the resevoir a few times to make sure I flush out the whole system of any old fluid and air bubbles.

    Once done, tighten everything back up and test the pedal. I bet you will find it will be much harder and actually make that disk and caliper work properly.

    Getting rid of the old rubber hose from the master cylinder to the caliper and using a braided stainless one will also help. You would be surprised how much those old rubber hoses bulge when you do a panic stop. And when they burst, you not only have no brake, but one hell of a mess to clean.
    #4
  5. Boxer Metal

    Boxer Metal Mad Scientist

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    Take the caliper off and get it bellow the master cylinder. Stick something between the pads that is a similar thickness to the brake rotor before you start pumping the brakes.
    #5
  6. DaveBall

    DaveBall Long timer

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    I know everyone has their favorite methods to do stuff, some like to get overly complicated. I would much rather just get the job done and spend the rest of the time riding the bike.

    I see no reason whatsoever to remove the caliper, unless you are replacing the pads. But, if you want to spend extra time removing the caliper, and either raising it above the resevoir or haning it down below it, and blocking the pads, feel free to do so. Once you have done that a few times and spent the extra time and effort to get a some what usable rear brake, put it all back together and try reverse bleeding. Done in half the time and end up with a very usable rear brake that will actually lock up if your press too hard on the pedal.

    I even reverse bleed my front brakes and get it done much faster. Why the heck would I want to spend a bunch of time pumping the brakes, hold them down and try to bleed the caliper on the other side of the bike?
    #6
  7. boxerboy81

    boxerboy81 Stay Horizontal

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    If air rises, why would bleeding work better with the bleed nipple at the bottom?

    I also like the retro flush technique as it's quick and simple and also gives you the chance to clean out the base of the reservoir. When did you last do that? You may find a film of something at the base and by emptying it and wiping it clean the system stays in a generally better state.

    When the reservoir is empty, it's very easy to inspect for crud that gets flushed into the reservoir. It's usually well seen in the first flush.

    Doing it the conventional way, getting the bleed nipple highest makes sense to me. The easy on bike method is to just rotate the caliper insitu. Undo the torque arm, loosen the axle clamp bolt/nut and it's a simple task to move the caliper clockwise.
    #7
  8. pbarmy

    pbarmy Long timer

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    Who said air rises?
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  9. bmwrench

    bmwrench Long timer

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    Yep, air rises. If the master cylinder is located properly, air will rise through the system and exit the vent port in the master cylinder. However, the brake line and hose on these bikes follow a torturous route: first upward from the master, across the frame, then down to the caliper. I use a Vacula, an air-powered bleeding device, but before I had one, I used the hang the caliper trick for years.
    #9
  10. mikejet

    mikejet KlrKid

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    Thanks everyone for the input. I did clean everything out ( restored the bike ) rebuilt the brake pedal pump - got new brake lines - etc... I like the reverse bleed idea , especially because I only have 2 hands :D Think I`ll give that a whack.

    Thanks - Mike
    #10
  11. bmwrench

    bmwrench Long timer

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    Only two hands? No wonder you're having trouble!

    Here's a handy tip-and I don't know how short your arms can be before this doesn't work-Stand on the left side of the bike, reach underneath it and work the brake pedal with your left hand and the bleeder with your right.
    #11
  12. boxerboy81

    boxerboy81 Stay Horizontal

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    Ever farted in the bath? :wink:
    #12