Results 1 to 6 of 6
  1. #1
    mtbr member
    Reputation:
    Join Date
    Jun 2009
    Posts
    214

    Problem during M596 bleed - oil leaking from the reservoir

    Hi all,

    I own a M596 2012 rear brake. I find it very good, except I need to pump the brake a few times to get it brake with more power (and also the lever gets firm after doing that). Even during long descents, when I pump the lever it is firm for only a second or two.
    So I tried to bleed it.

    I have 2 syringes, one with a M4 i think fitting, that fits the reservoir bleed port like a glove. The other syringe is on the caliper connected with the plastic tube (like Shimano recommends it).

    When I tried to push fluid from the caliper to the lever reservoir, it started to leak mineral oil at the place where the reservoir cap and the rest of the lever meet. Same thing when I pushed from the lever syringe to the caliper. Of course I didn't push like a maniac, but very slowly.

    Something is wrong, but can't tell what. Then I removed the reservoir top cap, found another screw that holds the metal plate over the rubber membrane so it doesn't leak oil. Either the membrane isn't sealing, something is missing or the membrane isn't sealing like it should. Therefore I opened the lever and removed the reservoir top cap.

    This is the picture taken from the web (since I didn't take pics with the top cap on):


    There are 2 screws. One on the left that lets you enter the bleed port, the second one (the one with the torx screw head) that keeps the top cap on the lever.

    After removing the right bolt (the torx one) the inside looks like this:


    See the metal plate covering the membrane, with one torx screw on the left (hard to see, this black thing on the left).

    After unscrewing the last torx screw under the top cap, you can see a white plastic part under it (so the screw presses it, then the plastic thing presses the metal plate which presses the membrane to seal oil). As you can see, I saw that under the right torx screw (which was removed when the top cap was going off the reservoir) there isn't any plastic part.



    Removing the metal plate, gets us to the membrane:



    After carefully removing the membrane, I can acces the oil in the reservoir:


    I tried to bleed the brake old style, pushing the lever so the oil goes to the caliper syringe. Also tried to push the oil from the caliper to the reservoir (removing it before spilling with the other syringe). Some bubbles had risen from the compensating port at the reservoir when the lever was operated pushing the oil to the caliper syringe.
    I saw a little improvement on the brake, but it still need to be pumped to get firm and to increase power.

    What could be the problem ? The missing plastic washer/part on the other torx screc (but the plastic reservoir top cap should be pressing it when the screw is tight. Checked the membrane - no holes or anything that would indicate it is damaged.

    The top syringe screws right into the lever bleed hole, oil leaks right trough the membrane. Really, very similar to the 2012 bleed kit with the yellow funnel or what it is called:
    http://www.slanecycles.com/bmz_cache...ge.650x650.jpg

    Any advices to get the brake bleed properly ?

  2. #2
    mtbr member
    Reputation:
    Join Date
    Jul 2007
    Posts
    304
    I bleed them the old fashioned shimano way - prior to funnels - hose on caliper bolt, topping oil after I removed the hardware like on your last image (you just have to top the oil more frequently - reservoir is not horizontal).
    Try it the oldfashined way, just make sure that oil can get out - maybe the caliper syringe pressure is preventing it - just connect the hose and let it drip.

    Bled 2 pairs so far without issues.

  3. #3
    mtbr member
    Reputation:
    Join Date
    Dec 2006
    Posts
    1,252
    If you are using a syringe and not the plastic Shimano funnel, its possible that the threads on the syringe are bottoming out in the port before the syringe fitting clamps down on the reservoir cap. . This confounded me till i figured it out. Unllike most bleed ports, this one is designed so the yellow funnel acts as both a topoff funnel AND as clamp to hold the res cap down tight on the res seal. (just like the bolt does when its all together.) If the syringe isnt clamping down tight on the cap when the threads are fully engaged, oil will push past the seal. Are you using an Avid syringe? I figured out a way to stack a few small washers of just the right size around the fitting on the syringe to take up the extra space so it would clamp tight while bleeding, then no more leaks from the reservoir seal. Or just get the Shimano funnel. And whatever internal parts are missing, you need them!
    '14 rocky mountain altitude, rally edition
    '11 transition blindside

  4. #4
    mtbr member
    Reputation:
    Join Date
    Jun 2009
    Posts
    214
    Quote Originally Posted by Goran_injo View Post
    I bleed them the old fashioned shimano way - prior to funnels - hose on caliper bolt, topping oil after I removed the hardware like on your last image (you just have to top the oil more frequently - reservoir is not horizontal).
    Try it the oldfashined way, just make sure that oil can get out - maybe the caliper syringe pressure is preventing it - just connect the hose and let it drip.

    Bled 2 pairs so far without issues.
    Thanks Goran,

    in the end I did it the way you said - like older XT/SLXes - plastic hose on the caliper, opened the reservoir and adding oil to it when the reservoir oil levels were low. I can see mayor improvements in the power, but still need to pump the lever once or twice to get it stiff like it should be.
    Quote Originally Posted by dwyooaj View Post
    If you are using a syringe and not the plastic Shimano funnel, its possible that the threads on the syringe are bottoming out in the port before the syringe fitting clamps down on the reservoir cap. . This confounded me till i figured it out. Unllike most bleed ports, this one is designed so the yellow funnel acts as both a topoff funnel AND as clamp to hold the res cap down tight on the res seal. (just like the bolt does when its all together.) If the syringe isnt clamping down tight on the cap when the threads are fully engaged, oil will push past the seal. Are you using an Avid syringe? I figured out a way to stack a few small washers of just the right size around the fitting on the syringe to take up the extra space so it would clamp tight while bleeding, then no more leaks from the reservoir seal. Or just get the Shimano funnel. And whatever internal parts are missing, you need them!
    Yeah, though about this also. But the membrane is pressed by the two bolts (one right to the bleed port on the lever, one under the cap on the left side - none of them are unscrewed while the bleed port is opened) that press the metal cover over it.
    Because of that I can't see why there should be any problem using a old Avid bleed syringe with its M4 fitting.

    None of the parts are missing. Only if Shimano forgot to put them in during assembly.

  5. #5
    mtbr member
    Reputation:
    Join Date
    Dec 2006
    Posts
    1,252
    Pretty sure the cap needs to be clamped down too for full sealing of the membrane, the inner metal piece isnt stiff enough to clamp it evenly. You will need to shim the avid fitting with washers like I did or use the Shimano funnel. Why else would mine leak without the shims, but didnt with them?. But... mine were xts, I think the internals are the same but could be different. At least try it. Easy way to see is, try bleeding them with your setup, but have someone "clamp" the cap down between thumb and forefinger near the bleed port. When I tried taht with mine, is when I realized what was going on.
    '14 rocky mountain altitude, rally edition
    '11 transition blindside

  6. #6
    mtbr member
    Reputation:
    Join Date
    Jun 2009
    Posts
    214
    @ dwyooaj
    I believe You. Thanks for all Your help. I'll try to find some shims or something similar that will ensure the top cap is pressing the membrane. Then I'll report back, probably with similar finding like yours .

Posting Permissions

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