Ridiculous Resistance in the lines when bleeding M785 XT brakes- Mtbr.com
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  1. #1
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    Ridiculous Resistance in the lines when bleeding M785 XT brakes

    I've noticed that whenever I try to bleed my rear brake there is a ridiculous amount of resistance against my bleeder syringe. I'm no Arnold, but it takes almost all of my strength to get a cc of mineral oil into my brake lines in 5-10 seconds.

    Basically what I'm doing is:
    1) Unscrew the top screw on the brake caliper reservoir and attaching a "catch" syringe
    2) Loosening the bleed valve counter clockwise about 1/2 a turn (any more and fluid leaks out the sides while injecting fluid)
    3) Attaching a large syringe with hose attached to the bleeder valve and injecting.

    I've successfully bled these brakes in the past and just figured the resistance was normal, but it's definitely just too difficult to bleed at the moment. I usually run about 20-30cc of mineral oil through the system to make sure all the air is out, but it's just becoming damn exhausting.

    Is there something terribly wrong, and has anyone else experienced this problem?

    Thanks
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  2. #2
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    Is the catch syringe "tightening" the nipple? Once during a bleed, I had the syringe rotate the nipple slightly under the weight of the fluid and essentially closed the bleed port. Just something to check/watch.

  3. #3
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    Quote Originally Posted by in the trees View Post
    Is the catch syringe "tightening" the nipple? Once during a bleed, I had the syringe rotate the nipple slightly under the weight of the fluid and essentially closed the bleed port. Just something to check/watch.
    I wish that were the case. I've loosened the bleed valve significantly and tried to push fluid through with little success
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  4. #4
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    Re: Ridiculous Resistance in the lines when bleeding M785 XT brakes

    The bleed port only needs to be opened 1/8 to 1/4 turn. If you go farther, you start to close/completely unthread it.

    If you have to force fluid, there is almost certainly something wrong. Is the reach dialed out?

    I would highly suggest grabbing a bleed funnel and doing a gravity bleed, by the way. It really is much easier.

  5. #5
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    Quote Originally Posted by wschruba View Post
    The bleed port only needs to be opened 1/8 to 1/4 turn. If you go farther, you start to close/completely unthread it.

    If you have to force fluid, there is almost certainly something wrong. Is the reach dialed out?



    I would highly suggest grabbing a bleed funnel and doing a gravity bleed, by the way. It really is much easier.
    That's a great idea ill gravity bleed it tomorrow.
    I have everything "opened up" including the free stroke and top fill screw. When you the reach, are you referring to the knob that allows me to change the lever position?
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  6. #6
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    As far as gravity bleeding, do I just simply keep a funnel reservoir full of mineral oil and just open up the bleeder valve to let the oil drain down? I don't need to depress the lever or anything and open and close the bleeder valve do I?

    Thanks for your help
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  7. #7
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    The reach adjusting knob/screw is what controls how far the lever blade is from the handlebar.

    When you do a gravity bleed, you'll need to open the system at both ends and have a general downward path to the caliper. Gently pull the lever a few times, and you should see fluid begin to slowly advance out of the caliper.

    I usually fill the funnel about half way, and that's fine, but you may need to add some extra fluid if there is a bunch of air in the line.

    When air stops coming out of the caliper (you will feel the lever significantly firm up) close the bleed port on it, and then gently stroke the lever until bubbles stop coming out. Incline the lever up 15ish degrees from horizontal and repeat, then down 15 degrees from horizontal.

    That should take care of it.

  8. #8
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    Do it how Shimano intended and you'll prob have no troubles, i.e. bleed it from the MC down to the caliper, letting gravity do the work AND use the Shimano open cup instead of the closed syringe. Never had an issue bleeding XTs or XTRs using the correct method.
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  9. #9
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    Okay so I'm stumped
    I just tried to gravity bleed the system and I could barely get any mineral oil to drain though with both ends open.

    I admitted defeat and dropped it off at my trusty LBS - will update when they figure out what's going on.
    Last edited by Ben_Im; 03-29-2014 at 11:00 AM.
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  10. #10
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    UPDATE:

    Just picked up my bike from the LBS that had a hell of a time bleeding my brakes. Apparently there was a chunk of oil in my brake lines had completely sludged. I don't know how they managed to eventually get it out, but I guess that's why they're my trusty LBS. Also, not sure why it occured in the first place. I will admit that I skimped out and ended up using drugstore mineral oil (big no no, I just found out). I had them completely flush the system with new shimano fluid and everything is working perfectly now.

    Glad that's done and over with.

    Thanks everyone for your input.
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  11. #11
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    Quote Originally Posted by Ben_Im View Post
    I will admit that I skimped out and ended up using drugstore mineral oil (big no no, I just found out).
    Good lesson learned. There's a difference between drug store mineral oil and a mineral based hydraulic fluid.
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  12. #12
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    Quote Originally Posted by Ben_Im View Post
    Also, not sure why it occured in the first place. I will admit that I skimped out and ended up using drugstore mineral oil (big no no, I just found out).
    It could be worse, at least you didn't put vegetable oil in your brakes, in which case you could honest say "man, my brakes are fried!" And yes, in the old days, I have seen people do that. I've also head of people putting vegetable oil in their forks, but that's another story.

    But yeah, stick to Shimano's hydraulic fluid. It works better and doesn't do bad things like turning into sludge and gumming up the works.

  13. #13
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    In a bind, I can see using a substitute, but if it's not an emergency, then have never seen the point of not using the correct fluids. Glad they got you sorted, guessing maybe they snaked the line or something to that effect.
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    Apparently they tried creating vacuum from the bleed port while pushing fluid through the fill hole, then reversing and pushing fluid through the bleed port. The back and forth pressure must have dislodged it somehow. They did some other tricks like holding down the lever while doing something else that I didn't quite catch.

    Hey everyone, captain obvious here, but please use Shimano brake oil if you have shimano brakes! Hopefully nobody repeats my mistake.
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  15. #15
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    Quote Originally Posted by Ben_Im View Post
    Hey everyone, captain obvious here, but please use Shimano brake oil if you have shimano brakes!
    While obviously it's fine to use Shimano brand brake fluid, it's not necessary. Just make sure that you use a high quality Mineral Based Brake Fluid or known equivalent (NOT drug store mineral oil). Do a little research and you will find there are several compatible fluids, but they are ALL Mineral Based Hydraulic Fluids, not drug store laxatives and make-up remover. Common sense can go a long ways.
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  16. #16
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    The only problem is that older pre-2012 Shimano XT lever bodies say "MINERAL OIL" right on the reservoir. Newer XT brakes now say "SHIMANO MINERAL OIL" so I wonder if it became enough of a misunderstanding that they had to relabel the newer lever bodies.
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  17. #17
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    Quote Originally Posted by Ben_Im View Post
    The only problem is that older pre-2012 Shimano XT lever bodies say "MINERAL OIL" right on the reservoir. Newer XT brakes now say "SHIMANO MINERAL OIL" so I wonder if it became enough of a misunderstanding that they had to relabel the newer lever bodies.
    Again, common sense goes a long way.
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  18. #18
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    Unfortunately common sense is not always so common. Hope nobody repeats my mistake
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  19. #19
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    Other mineral oils may work okay, but Shimano (naturally) only recommends their proprietary oil. It also doesn't hurt that Shimano's oil has a higher boiling temperature than even DOT 5.1.

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