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Black streaks in brake fluid??

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    #16
    Thanks Steve,

    Re the lever removal to push the piston in further... had already done that (see post 6).

    Re the turning of the bars and taping the lever hard in.... I have/had done both and also note that if the lever is tapped a hundred times and pulled in hard half a hundred times while the bars are turned hard left and then right, the combination of lever vibration and master cylinder angle will also clear the trapped air. Pays to cover the MC with glad wrap (cling film) held in place with a rubber band, to avoid squirting fluid all over the tank etc.

    I tried installing a 3.5mm by 13mm dia plastic spacer and found that it was too big to allow MC priming. I ground it down to 2.5mm and re-installed. It works great. My previously huge (and prolonged) fluid fountain is now a mere squirt. Lever travel is now fine. It was about 35 -45mm of travel before engaging and is now about 13 - 15mm. (not perfect, but close)

    I haven't taken it for a ride yet to bed in the new organic pads (which don't appear very sticky) but am confident that I have resolved the lever travel.

    Once sure that all is well I will post an explanation of how the modification can be used to address at least some excessive lever travel issues.

    Another thing I noticed was that the piston can be slightly depressed in if the brake lever assy is moved too close to the throttle grip assy (preventing the heel of the lever from fully returning). This could be problematic if it resulted in the seal being prevented from clearing the relief port.



    Originally posted by Steve View Post
    Another function of the compensating port is to compensate for liquid volume due to heat expansion. It is natural for the claipers to get warm while riding, due to the pads dragging ever so lightly on the disks. This warms up the brake fluid, causing it to expand. If the compensating port is blocked, the only way the fluid can expand is to press on the pads, dragging them harder. Dragging harder adds heat. Heat adds expansion. Expansion drags the brakes harder.

    Would you believe that even a 1300cc V-4 Yamaha Venture in first gear can not overpower a locked rear brake to make it the last 200 yards to home?
    Had to get out the Leatherman and open the bleeder for the rear brake to get home.

    Moral of the story: whenever cleaning the master cylinder, poke something through that hole to make sure it's open.


    Colin, now to your lever travel problem:
    There could be an air bubble trapped in the master cylinder. Remove the lever, use a large Philips screwdriver to push the piston in. It will travel farther than the lever can push it, usually getting rid of that troublesome space at the end of travel inside the bore.

    If that doesn't work, there is one last-ditch method. Rotate the handlebars so the output of the master cylinder is the lowest point of the assembly. Squeeze the lever, tie it to the handlebar to keep it squeezed, leave it overnight. I have talked to several guys that have done this to allow the air bubbles to migrate up, through the assembly on its own, but it does take several hours to happen.

    .

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      #17
      Originally posted by Steve View Post
      Another function of the compensating port is to compensate for liquid volume due to heat expansion. It is natural for the claipers to get warm while riding, due to the pads dragging ever so lightly on the disks. This warms up the brake fluid, causing it to expand. If the compensating port is blocked, the only way the fluid can expand is to press on the pads, dragging them harder. Dragging harder adds heat. Heat adds expansion. Expansion drags the brakes harder.

      Would you believe that even a 1300cc V-4 Yamaha Venture in first gear can not overpower a locked rear brake to make it the last 200 yards to home?
      Had to get out the Leatherman and open the bleeder for the rear brake to get home.

      Moral of the story: whenever cleaning the master cylinder, poke something through that hole to make sure it's open.
      .
      The brakes on any vehicles should be able to develop enough torque hold back the motor. The ability to decelerate a vehicle from top speed at high g's is higher the motor torque plus multiplication out of the drivetrain.

      Your brake lock-down is kind of the chicken-egg debate, but in my opinion goes back to the blocked port issue. When we had thermocouples in the brake pads on vehicles under off-brake conditions such as long distances on highways without brake applys, would have the brake pads only at 80-100F, and the caliper pistons and fluid would be cooler then that. If the calipers are working correctly, and the pads are free in their brackets, there should be 0.010 to 0.015" clearance between the pads and rotors. If the O-Rings have lost their compliancy, then the roll back will not be as much. But that is a problem with older brake parts or those that have gotten very hot, the rubber hardens.

      Anyway, if there was the clearance necessary then the fluid should not have expanded from heat. But if you've got a blocked port, with some good braking I'm sure the heat did have a factor and the fluid expansion just applied the brakes harder. But just going down the road should not be heating up the fluid.

      Comment


        #18
        Originally posted by TooManyToys View Post
        The brakes on any vehicles should be able to develop enough torque hold back the motor. The ability to decelerate a vehicle from top speed at high g's is higher the motor torque plus multiplication out of the drivetrain.

        Your brake lock-down is kind of the chicken-egg debate, but in my opinion goes back to the blocked port issue. When we had thermocouples in the brake pads on vehicles under off-brake conditions such as long distances on highways without brake applys, would have the brake pads only at 80-100F, and the caliper pistons and fluid would be cooler then that. If the calipers are working correctly, and the pads are free in their brackets, there should be 0.010 to 0.015" clearance between the pads and rotors. If the O-Rings have lost their compliancy, then the roll back will not be as much. But that is a problem with older brake parts or those that have gotten very hot, the rubber hardens.

        Anyway, if there was the clearance necessary then the fluid should not have expanded from heat. But if you've got a blocked port, with some good braking I'm sure the heat did have a factor and the fluid expansion just applied the brakes harder. But just going down the road should not be heating up the fluid.
        True, there should always be some clearance betwen the pads and rotors. That is the very reason I fitted up a set of o rings instead of trying to replace the rubber sleeves that are fitted to one pin in stock calliper configuration. The new setup provides instant and complete release. I've run the bike this way for a couple of years now.

        The other thing that can happen when that port is blocked, is the brake fluid will expand in the system just through sitting in the sun. I had this happen on a couple of very hot days after work, and had to release the pressure at the banjo, just to ride the bike home (a short distance so no dramas).
        :) The road to hell is paved with good intentions......................................

        GS 850GN JE 894 10.5-1 pistons, Barnett Clutch, C-W 4-1, B-B MPD Ignition, Progressive suspension, Sport Demons. Sold
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