1981 R 100 RT rear brake problem! What did I do wrong?

Discussion in 'Airheads' started by Mikepotter86, Mar 16, 2013.

  1. Mikepotter86

    Mikepotter86 Been here awhile

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    I just swapped the brake lines and front master cylinder off my 81 R100Rt, replacing with new steel lines from spiegler, and a brand new OEM MC.

    Before the operation the front had no brake pressure due to a leaky MC, with the new MC and the new steel brake lines the front is working great.

    Before the operation the rear was fine, but I figured I might as well swap the line out since they're probably 30 years old, but after installing and bleeding the rear, it has no pressure. I bled the system for what seemed like hours, but no pressure builds, even once the air bubbles are all gone. I don't mean it is spungy, it is like I have no brakes! With the bleeder closed I have no leaks that I can see.

    I am sure I did something stupid. Help me out here!
    #1
  2. Married Man

    Married Man Been here awhile

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    I've had the same issue after replacing the rear mc and brake line. I tried pushing and sucking the fluid through with the same poor results. I got pressure after I removed the caliper, put a wedge in between the brake pads, and strung it up so that the bleeder was on top. I used a one-way valve brake bleeder until I got no air and then let it sit for a day and bled it again. Teflon tape the bleeder valve to keep air out. I have good brake pressure now.
    #2
  3. Plaka

    Plaka Brevis illi vita est

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    What does this mean: "...swap the line out."?
    #3
  4. Paul_Rochdale

    Paul_Rochdale Been here awhile

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    Replace the brake hose for a new one.
    #4
  5. TINK

    TINK Been here awhile

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  6. TINK

    TINK Been here awhile

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    +1 on the Teflon tape.. oh, ya, don't forget to wedge the pads.
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  7. hardwaregrrl

    hardwaregrrl ignore list

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    Have you disconnected the line from the caliper to insure there isn't a block in the new line?
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  8. pbarmy

    pbarmy Long timer

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    Everything I've read says hang the caliper upside down,this puts the bleeder at the bottom,allowing for any trapped air to escape.
    #8
  9. Mikepotter86

    Mikepotter86 Been here awhile

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    Thanks for all the advice! I will try a new approach when I next have use of a garage, or when the weather improves.
    #9
  10. Slipkid

    Slipkid Long timer

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    I have had a couple of difficult brake bleeding sessions. The best trick I found is to not just pump the brakes up and then open the bleeder when compressed but to always remember to pump the brake pedal or lever many times before starting the pump and purge process with the bleeder wide open. I think this gets the brake fluid and air moving towards the vent. Also add a length of flexible hose to the bleeder to catch the fluid and create a liquid trap.

    Just keep trying and don't get any on the paint.
    #10
  11. lucky6600

    lucky6600 Been here awhile

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    Do you have the rear caliper all screwed/tide down at it's position while you are trying to "bleed" out all the air?


    If you did, lose the support arm and move the caliper angle little bit (rotate it) having the bleeder facing up, let gravity does it's job. You might find more air still trapped in there.

    worth a try and ask me why I know that
    #11
  12. DaveBall

    DaveBall Long timer

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    I see that everyone wants to bleed the brakes using the most time consuming and difficult methods.

    1. Leave everything mounted as it should be.
    2. Go to local pharmacy / drug store and purchase 2 large syringes that hold at least 30cc of fluid. and purchase some clear surgical tubing from them as well, about 2 feet is more than enough.
    3. Use 1 syringe to suck all the fluid out of the master cylinder and dispose of it in a disposable container.
    4. Using the 2nd syringe attach about 12 inches of tubing and suck up some new brake fluid.
    5. Attach the tubing and the 2nd syringe to the bleeder on the caliper, and crack the bleeder.
    6. Slowly inject the fluid in thru the bleeder while having someone hold the brake pedal slightly depressed. I just put a 1 quart paint can on it.
    7. Close the bleeder and refill the syringe.
    8. Repeat steps 5 and 6, watching the master cylinder for bubbles and remove excess fluid as required.

    I have done the above procedure on a lot of friends bikes with "useless non working rear disk brakes" and every one of them has ended up with an excellent rear brake. This procedure is simple and once you do it, you will be very surprised how easy it is to get a good solid pedal, and a brake that will actually stop the bike.

    I also use this same procedure on front brakes if I have had to remove any lines, or I just can't get the spongy feeling out of them using the normal methods.
    #12
  13. hardwaregrrl

    hardwaregrrl ignore list

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    +1 In your neck of the woods, hit up a feed and seed for the syringe.

    #13
  14. jackd

    jackd Long timer

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    Is it just me or does this statement make no sense to anyone else? Why would you put the bleeder at the bottom when any trapped air in the caliper would be floating up toward the top of the chamber, where it can not be expelled? I bleed lots of disc brakes in my line of work and you always go for the uppermost bleed screw to allow the bubbles to leave the unit.
    #14
  15. Plaka

    Plaka Brevis illi vita est

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    I use a small electric vacuum pump and a receiver for the fluid. Brake bleeding is incredibly fast zero hassle process. Any brake, any time, anywhere (that has power). This is what shops use, for a reason. I can do a full flush in about 5 minutes and most of that time is getting the pump off the shelf and hooked up. if the system is dry I put on the vacuum first then add the fluid. Gets pushed right through driving any air ahead of it.

    I notice MityVac makes vacuum pumps. Vacuum pump and receiver, runs of an air compressor.
    http://www.amazon.com/Mityvac-6830-...=UTF8&qid=1363830686&sr=1-13&keywords=mityvac



    This will pull vastly more vacuum than you need but the pric is right and you can play some other games with it (I use a bigger one to preserve food as well as do HVAC work). The easy way to use it would be with a cheapo portable air tank. Evacuate the tank and then use the tank to bleed to a receiver---or you could just work right off the pump into a receiver.

    www.amazon.com/Mityvac-6830-Brake-Bleeder/dp/B000JFN9WC/ref=sr_1_13?s=automotive&ie=UTF8&qid=1363830686&sr=1-13&keywords=mityvac

    pumps are just getting so cheap there isn't a reason not to have one. it's a tool that makes you happy every time you use it.
    #15
  16. dm635

    dm635 I Roll

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    This works. On the old bimmers I drive bleeding the clutch is a real pain that leaves the clutch pedal at the floor where it does you no good. I have an oil squirter can I use to bleed my clutch lines now from the bleeder.
    #16