Results 1 to 7 of 7
  1. #1
    the new Gilbert Grape
    Reputation: laffeaux's Avatar
    Join Date
    Jan 2004
    Posts
    5,182

    Shimano XT m765 hydro - bleeding - initial install

    I'm helping a buddy install a set of Shimano XT (m765) hydro brakes. They did not come pre-bleed. Out of the box the hoses had no fluid, and two bottles of fluid were included in the box.

    Everything is installed, but we're not able to get any pressure at the lever. Shimano's instructions are pretty feeble, but we've attempted to follow them to clear the air from the lines but had little luck. When squezeing the levers with the bleed valve open, fluid is moving through the system and out the bleed valve, but there's no pressure at the lever. When the bleed valve is closed (done either with the lever squeezed or not), the results are the same - no pressure at the lever. Also there are no air bubbles coming out into the reservoir when it is repeatedly squeezed (there were a few initially, but none now).

    What's the trick? How do you clear the lines of air?
    Each bicycle owned exponentially increases the probability that none is working correctly.

  2. #2
    mtbr member
    Reputation: vk45de's Avatar
    Join Date
    Jan 2009
    Posts
    1,083
    The caliper is probably the main air trap you have to worry about. Here's how I fill my system:
    - take caliper off of bike, pad off of caliper
    - open caliper bleeder valve then close it a finger-tight (so you can open it w/o wrench)
    - attach syringe to bleeder valve
    - hold caliper such that the part where the hose comes in is on top
    - open bleeder valve and pump fluid in (mineral oil in your case)
    - if it's enough fluid to fill caliper (you'll have to guess - or pull the hose off to be sure), inject a little more so have some in the hose
    - cycle the fluid in and out of the caliper to dislodge any air bubbles from hose side of caliper (bubbles will go into hose) - you can tap the caliper occasionally with a screwdriver handle to dislodge blubbles
    - turn caliper so your bleeder valve is up
    - cycle fluid to remove bubbles from bleeder valve side of caliper - again, you can tap the caliper
    - close bleeder valve and refill you syringe w/ fluid (repeat these as much as necessary)
    - reattach syringe, open valve, suck some fluid in first (to avoid introducing bubbles)
    - pump fluid through brake line until fluid rises into reservoir
    - cycle fluid w/ syringe to dislodge any bubbles in reservoir
    - close system and test for pressure

    Oh sh!t, I got hardcore. what you do not is pump fluid from caliper and remove fluid that comes into reservoir. What you probably have are bubbles that are closer to the caliper and they won't move up that fast unless you pump their as$ess up.

  3. #3
    mtbr member
    Reputation:
    Join Date
    Apr 2004
    Posts
    7,880
    Is that common, brakes coming not pre-bled, no fluid in the lines, owner gets to start from scratch? Is that a Shimano thing, an XT thing, do other manufacturers just toss the new owners un-bled brake systems? I'd like to know because I just ordered some Elixir Rs and I'm expecting them to be pre-bled. (insert emoticon of a guy with his fingers crossed).
    A blind man searches in a dark room for a black hat that isn't there. Dashiell Hammett

  4. #4
    the new Gilbert Grape
    Reputation: laffeaux's Avatar
    Join Date
    Jan 2004
    Posts
    5,182
    Quote Originally Posted by xcguy
    Is that common, brakes coming not pre-bled, no fluid in the lines, owner gets to start from scratch? Is that a Shimano thing, an XT thing, do other manufacturers just toss the new owners un-bled brake systems? I'd like to know because I just ordered some Elixir Rs and I'm expecting them to be pre-bled. (insert emoticon of a guy with his fingers crossed).
    I use Magura brakes on my own bikes, and they are pre-bled from the factory. Until seeing these brakes, I would nto have thought that anyone shipped them this way.
    Each bicycle owned exponentially increases the probability that none is working correctly.

  5. #5
    mtbr member
    Reputation: vk45de's Avatar
    Join Date
    Jan 2009
    Posts
    1,083
    Quote Originally Posted by xcguy
    (insert emoticon of a guy with his fingers crossed).
    wish granted

  6. #6
    mtbr member
    Reputation:
    Join Date
    Jan 2004
    Posts
    324
    Quote Originally Posted by laffeaux
    I'm helping a buddy install a set of Shimano XT (m765) hydro brakes. They did not come pre-bleed. Out of the box the hoses had no fluid, and two bottles of fluid were included in the box.

    Everything is installed, but we're not able to get any pressure at the lever. Shimano's instructions are pretty feeble, but we've attempted to follow them to clear the air from the lines but had little luck. When squezeing the levers with the bleed valve open, fluid is moving through the system and out the bleed valve, but there's no pressure at the lever. When the bleed valve is closed (done either with the lever squeezed or not), the results are the same - no pressure at the lever. Also there are no air bubbles coming out into the reservoir when it is repeatedly squeezed (there were a few initially, but none now).

    What's the trick? How do you clear the lines of air?
    I had a similar problem with a new set of SLX brakes. Although they came pre-bled, I had to cut the hose to size, and install a new olive and end fitting, so the system was opened. I tried following the Shimano instructions and the instructions on the Park website, but no pressure at the lever.

    The wierd thing was, sometimes after tapping the calipers with a screwdriver and flicking the lines, I would get some pressure, but then if I would do a few more cycles of the the lever and opening the bleed nipple, the pressure would dissapear. I don't have a syringe, so I just had a tube going from the nipple into a bottle, submerged in fluid.

    When I first squeezed the lever, some fluid came out of the nipple into the tube, but subsequent squeezing of the lever and opening the nipple would not cause more fluid or bubbles to come out. The Shimano instructions say open the nipple 1/8 turn, Park says 1 turn, I expermiented with both, but the same results.

    There seemed to be no rhyme or reason why pressure would appear, and then further bleeding would make it dissapear, so I kept doing it till I got pressure, and then stopped. However, they are pretty mushy.

    I have bled many, many car and motorcycle brakes before, and never had this problem!

  7. #7
    PCC
    PCC is offline
    mtbr member
    Reputation:
    Join Date
    Sep 2005
    Posts
    1,046
    How timely. I just installed a set of BR-M765s on my buddy's bike (just created a thread about this). They came pre-bled but we're going to be cutting the rear hose down this coming weekend so we will be bleeding that system.

    WRT to bleeding brakes the procedure should be:
    Insert the yellow brake bleeding block into the caliper.
    Hook up the bleeder tube thingie at the caliper.
    Squeeze the brake lever, giving gentle pressure.
    Release the bleeder valve, allowing any fluid to escape.
    Close the bleeder valve (probably less than a half second open at max).
    Release lever.
    Check fluid level in the reservoir.
    Repeat until you are satisfied that there is no more air in the system.

    Absolutely make sure that you have not allowed the reservoir to completely drain out as this will introduce air into the system at the top of the system which you will then have to drive all the way through to the caliper to get out.

    As far as your brakes are concerned, it seems to me that you are reintroducing air into the system somehow. Try following the above procedure and see what happens. Keep at it. With a completely dry system it could take some time to fill the system with fluid as the air compresses when you squeeze the lever. You can even try pumping the lever a few times to build pressure until the lever feel firms up. Releasing the bleed valve will allow the air to escape.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •