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  1. #1
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    Shimano XTR M988 problems

    Recently bought a set of M988(trail) brakes from my LBS. Out of the box they were spongy and felt really horrible but I thought maybe they needed to be run in. Went out for a ride and I must say, they were bloody dangerous. Steep decents and air time totally kills the brakes. Not talking about anything DH riding just trail riding with drops no bigger than 3feet. Biting point is totally lost immediately when the bike is pointing down, up or in the process of a drop. It was to the point the lever is compressed all the way into the bar and still no "bite point" feel. After a couple of seconds later then, the bite point will return to normal, but still spongy, unlike my past shimano brakes. Never had this problem with avids.

    Thought it was bad factory bleeding and sent it back to my LBS for rebleeding and still the same problem persists - spongy on normal riding, no brakes on steeper decents and in the air. I am greatly disappointed at my XTR brakes as I thought they were very good brakes and worth the extra $ I forked out. I must say they are outright dangerous and unreliable on the trails. A couple of friends also have this spongy brake feel and was told it was quite common with some XTR brakes(race and trail)

    I have since emailed my local dealer about the problem but still awaiting their reply.


    Any of you having the same problem as well?

  2. #2
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    Sounds like a bad bleed. They are different to bleed from older Shimanos and they use a different bleed kit. They should not feel like that.

  3. #3
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    I had my lbs rebleed them, the problem went away for a few rides and came back after. Only worry it will get worse over time, and requires a constant bleeding to get them to work

  4. #4
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    It does sound like an air bubble in the braking system.

    It doesn't matter how many times they're bled, since it only requires the one time to do it right, and not everyone gets it right the first time. I've never relied on a Shimano out of the box bleed, since I usually cut the lines and bleed them as if they were freshly assembled. So I can't comment on Shimano's bleed (many know that Avid can't bleed their brakes worth a damn at all).

    Give the shop another chance, but for your own curiosity, ask them if they're using the Shimano bleeding kit. Maybe they'll let you watch.

    Of course, it is possible that something is wrong with the brakes, but that's something you'll have to work out with the shop. Otherwise, these brakes are really that good, and deserving of their reputation.
    May the air be filled with tires!

  5. #5
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    I have the 988 brakes on my Seven Sola with the RT86-S (XT Ice Tech) 6 bolt rotors.

    The brake setup was phenomenal for the first ~200 miles, but now the front brake has lost a great deal of grab. The lever feels normal (not "spongy" like the OP experiences) but power from the front now feels like a poorly-tuned V-brake. The rear still feels perfect.

    My LBS lightly sanded the rotors and pads yesterday, but on my ride today I found that the front brake is unchanged.

    My suspicion is that I may have damaged the pads on one very fast & wet descent. The brakes were shreaking and scaring away all the wildlife...and had much less power that run. I was hopeful all would turn to normal when they dried. The front did not return to normal--now upon inspection the pad surfaces are smooth...perhaps "glazed"...and definitely shiny. Is this normal? Might I have overheated the pads on that run?

    Note these are the metal variety of pad, (not the resin type offered) and I weigh 185 lbs.

    Should I just buy another set of pads to see if that fixes my problem? Has anyone else experienced this?

    Thanks and happy riding,

    Kurt

  6. #6
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    If it is still happening you might want to try replacing the cables as they might have a tiny hole or something going on in them.

  7. #7
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    Quote Originally Posted by Bikerturtle View Post
    I have the 988 brakes on my Seven Sola with the RT86-S (XT Ice Tech) 6 bolt rotors.

    The brake setup was phenomenal for the first ~200 miles, but now the front brake has lost a great deal of grab. The lever feels normal (not "spongy" like the OP experiences) but power from the front now feels like a poorly-tuned V-brake. The rear still feels perfect.

    My LBS lightly sanded the rotors and pads yesterday, but on my ride today I found that the front brake is unchanged.

    My suspicion is that I may have damaged the pads on one very fast & wet descent. The brakes were shreaking and scaring away all the wildlife...and had much less power that run. I was hopeful all would turn to normal when they dried. The front did not return to normal--now upon inspection the pad surfaces are smooth...perhaps "glazed"...and definitely shiny. Is this normal? Might I have overheated the pads on that run?

    Note these are the metal variety of pad, (not the resin type offered) and I weigh 185 lbs.

    Should I just buy another set of pads to see if that fixes my problem? Has anyone else experienced this?

    Thanks and happy riding,

    Kurt
    Swap your pads front to back and see what happens.

  8. #8
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    I installed new pads and the bike's back to ripping like an F1! Still a mystery how the originals could've roasted out in such a short period (and on the wet ride).

    This time I installed the resin/ cooling fin variety, in place of the outgoing metal/ cooling fin type. Incidentally, the late XTR pads are also available in resin and metal without the cooling fins, making 4 total pad choices. I look forward to learning whether the resin perform better than the metal.

    Will report back...

    Kurt

  9. #9
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    It is a very common issue for the brakes to very slowly leak at the crimp near the caliper. Eventually this contaminates the pads affecting performance... squeeze the levers hard and observe the crimp..

  10. #10
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    Baltik, you're right on the money.

    My mechanic found a leak at the piston(s) behind the pad. A slow leak, and perfect for contaminating the pads. Downside is I've toasted 2 sets of pads isolating the problem. Upside is Shimano is handling this very well...sending a complete new caliper and lever setup!

    Hope to have parts arrived & installed in a week or so. Will report back.



    Kurt

  11. #11
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    I've experienced the same issues with my XTR brakes as well. As ide from the banjo leaking, I also noticed leaking at the pistons. I'm on my third set of pads now... still waiting for the replacement set. The older versions were bombproof.

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