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  1. #1
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    Shimano XT M785's in the cold

    Have the newer series M785's proven to be more reliable in the cold in comparison to the M775's? First really cold ride of the season today, and had the usual caliper retraction issues on my M775's. I've never had leaking fluid, just pad drag.

    Lie to me, convince me to upgrade.
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  2. #2
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    I'll be riding my M785's in 25ish degree weather on Tuesday. I'll let you know if there's any difference between then and today (55 today).

  3. #3
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    I've ridden with mine in 12F weather with no issues.

    Sent from my Android - because Carrier Pigeons are slow!

  4. #4
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    I'm on M785 XT's and have ridden in mud, snow and down to around 20 degrees F and haven't had any issues with them leaking or sticking. They are incredibly loud when it's cold though, no loss of stopping power.

  5. #5
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    I'm not sure if it was due to the cold but my 988 XTRs have developed a leak over last winter at the master cylinder. I eventually had to replace them.

    They also got stiffer than usual in the cold but it wasn't a big deal.
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  6. #6
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    What is the symptom of a sticky caliper? It was about -5F this morning and my front lever had no play before activating the brake but it didn't seem to be dragging. Is this indicative of a sticky caliper?

    My rear brake hasn't worked well in a while so that lever was really soft and the brakes howl. Scouring the forum for a solution. I must have a leak even though I've never noticed oil on the calipers.

  7. #7
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    Quote Originally Posted by bedwards1000 View Post
    What is the symptom of a sticky caliper? It was about -5F this morning and my front lever had no play before activating the brake but it didn't seem to be dragging. Is this indicative of a sticky caliper?

    My rear brake hasn't worked well in a while so that lever was really soft and the brakes howl. Scouring the forum for a solution. I must have a leak even though I've never noticed oil on the calipers.
    Biggest problem with cold weather is leaking fluid....I have to refill my brakes once a winter....You can notice the oil on the caliper after it warms up...

    Check your pads it looks like black dirt..the leaking is obviously very small amounts.
    Wash the barkes in soap and water then...
    Put your pads in a old fry pan set the stove to medium heat...the fluid in and on the pads will burn off.....after about 15 mins let them cool and lightly sand of the carbon, re-install


    A sticky piston is a piston that does not retract away from the rotor....when bad you will notice a swishing sound as the rotor turns....and brake drag will increase.

    The non sticky piston move in and out much further than normal cause the volume from the master cylinder has to move something.

    Soft lever and howling brakes is a leak.....brake drag and noises while not braking is a sticky piston.

  8. #8
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    Thanks Jeff, So what's an overly firm lever a symptom of? I doubt I could hear any swishing above the sound of crunching snow.

    Is the cold weather leaking around the banjo clamp?

    I've never noticed any oil but I found this thread XT-XTR BR-M785 Warranty Brake Leaking Issue and the symptoms fit my problem exactly. See my post at the end. I'll look harder for some oil and see if I can find a shop to fix it.

  9. #9
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    Quote Originally Posted by bedwards1000 View Post
    Thanks Jeff, So what's an overly firm lever a symptom of? I doubt I could hear any swishing above the sound of crunching snow.

    Is the cold weather leaking around the banjo clamp?

    I've never noticed any oil but I found this thread XT-XTR BR-M785 Warranty Brake Leaking Issue and the symptoms fit my problem exactly. See my post at the end. I'll look harder for some oil and see if I can find a shop to fix it.
    To firm a lever is often due to overfilling the reservior....I have never had that problem.

    The cold weather leak is always from the piston seals for me....I think maybe just a tad from the master cylinder piston seals as well.

    My brakes a XTRs.

    You can hear thw swishing when you spin the wheel with the bike up on the stand.

  10. #10
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    So how do you maintain any braking power in the winter if the cylinders are pissing oil all over the rotors? Mine do look like they are leaking around the pistons in the cold. They are M775s not 785s.

  11. #11
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    Mine are actually M775s. I'm riding around 0F and the back piston is leaking like a sieve. It was leaking some but now it seems to be leaking a lot. I popped both pistons out and cleaned up the pistons and seals but I didn't ride it today since I hadn't had a chance to test them.

    Jeffscott, more questions, do you bake off the oil in the pads? What temp? Can you do it with resin pads?

  12. #12
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    I'd go for some saints for better sealing perhaps? I ride M765 hydraulics with dual control. Got a leaky rear piston riding in sub 0F weather in Maine a few days ago, front brake is completely fine though.

  13. #13
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    Must be a Maine thing, that's where I am, Raymond. Where are you?

    I don't think I need to jump to saints. It sounds like it is hit or miss on all of these. Just in this thread we have leaky 765, 775 & 785 calipers. My front's are still great. I'll try new seals next.

  14. #14
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    Hmmm, I've heard that these brakes calipers are not user serviceable. Plus the BR-M765 run for like $80 a pair on eBay nowadays, I'm tempted to just switch out my rear caliper with a used pair from eBay and use everything else as backup. Luckily it's not really urgent since I do 80% of my braking with the front right now. Or maybe it's time for me to upgrade to some XTRs. I gotta stick with Shimano cause I want dual control, but I'm starting to wonder at what cost?

    I'm up in Waterville, low tomorrow is -6F with 9F high!

  15. #15
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    Quote Originally Posted by rogerfromco View Post
    I've ridden with mine in 12F weather with no issues.

    Sent from my Android - because Carrier Pigeons are slow!
    Me too, no issues at all. Still working great with no leaks.

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  16. #16
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    Quote Originally Posted by Crank Monkey View Post
    Hmmm, I've heard that these brakes calipers are not user serviceable. Plus the BR-M765 run for like $80 a pair on eBay nowadays, I'm tempted to just switch out my rear caliper with a used pair from eBay and use everything else as backup. Luckily it's not really urgent since I do 80% of my braking with the front right now. Or maybe it's time for me to upgrade to some XTRs. I gotta stick with Shimano cause I want dual control, but I'm starting to wonder at what cost?

    I'm up in Waterville, low tomorrow is -6F with 9F high!
    I've heard that a hope mini seal kit has piston seals that fit but I haven't' tried it. I would think a used caliper on ebay has the same chance of leaking as the one on my bike.

  17. #17
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    Leaking fluid

    Just my 2 cents here.
    I had the 775 and my rear was leaking at the caliper.
    Went to grab some rear brake and next thing I knew I was on the ground w a broken pelvis.
    Basically the rear brake lost all power due to the fluid loss/ fluid on pads.
    If you ever see leaking fluid on your brakes, don't ride them!!
    Shimano I need a new brake set ASAP

  18. #18
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    Quote Originally Posted by bedwards1000 View Post
    Mine are actually M775s. I'm riding around 0F and the back piston is leaking like a sieve. It was leaking some but now it seems to be leaking a lot. I popped both pistons out and cleaned up the pistons and seals but I didn't ride it today since I hadn't had a chance to test them.

    Jeffscott, more questions, do you bake off the oil in the pads? What temp? Can you do it with resin pads?
    YES I do bake the oil that accumulates in the pad....

    I wash the bike with soap and water, then put the pads in an old frying pan on the stove at med heat.....I cook them till the smoke gets very small....a lite sanding to remove the carbon and away I go....

    Yes I have done it with resin pads.....no problem

    Right now I have sintered metal pads they cook up fine too.

    Basically the issue is one of amount and time....

    Mine leak when it gets really cold, the time I spend going downhill is not enough to heat the pads up so they self clean.....on the other hand they brake okay at least for a while.

    The oil leak is not directly onto the pads but is mostly contained in the caliper by dirt and roost.

    In addition to the oil I also have salt and water getting into the pads....

    The guy that totally lost braking power may have an oil leak but I suspect that that was an iced up rotor...

    That occurs generally around -16 to -20 C with snow and no salt....the rotor gets hot you let the brake off...then the rotor melts the snow...a very thin layer of ice forms on the rotor...next brake absolutly zero braking...

    You have to hammer the brakes of and on as hard as you can...the thin film will crack off.....

    it doesn't melt off cause there is zero friction....(well it might if you have enough time and runout space).

  19. #19
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    Thanks for the long informative reply. I've experienced the ice on the rotors when my bike took an impromptu polar dip. I heated my pads this weekend but haven't tried them yet.

  20. #20
    West Chester, PA
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    I've done 4 or 5 rides with temps in the 30s since I got my XT 785 brakes, with no problems. But yesterday I was out really early and I think it was about 26-28 degrees. I was experiencing a weird thing where the lever travel would get much shorter on the first pull, but then if I did 2 or 3 pulls real fast I was getting the normal contact point I had set. I got off the bike at one point and watched the caliper very closely as I pulled. If I pulled the lever and let it go quickly, I could see the pads retracting very slowly (they would retract a little bit and then take another second to retract all the way).

    I have to figure out if this is fluid related or piston seal related. I was also wondering to myself if running regular pads instead of the the ice tech in the winter might be beneficial - to retain a little more heat in the caliper.

  21. #21
    West Chester, PA
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    Another update. I never messed with the brake last week. I was out again in mid-20s temps sunday morning, and had the very slow pad retraction issue again.

    Last night, temps got into the 40s so I took a few laps around my street and tested it - working fine. So there's definitely an issue when it's below 30. But only on my rear brake, front one isn't doing it.

  22. #22
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    I still don't have full power even after heating my pads. I can briefly get it back if I have a long downhill to heat up the rear brake but then it gets worse again after a while. I don't think it is leaking any more because I put a piece of paper between the piston and the pad and gave a few hard squeezes and I don't see any oil on the paper. Maybe I need to leave it in there during a ride.

  23. #23
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    My front brake lever has started to leak now that it is warmer say -6C to 4C...

    I will have to have a look...

    I did a messy bleed and got oil on the rear pads....a burn fixed them up nicely...

    Bedwards it may not be oil that is contaminating the pads....it might be salt and water...and because the brakes just down't get as hot in the winter they don't really get a good chance to dry out.

  24. #24
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    Yeah but the fronts stop like champs. I may try burning them longer. I went until the smoke stopped but maybe there was still some residual oil on them. I'd consider a new caliper but it seems like there is no guarantee that it would be much better.

  25. #25
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    Did you sand off the burn carbon from the pad surface and bed the brake afterward?

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