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  1. #1
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    Another Shimano SLX M666 (2012) Review

    I received my Shimano M666 brake set this morning. For those interested here's my initial review. These were installed on a Trek Soho and replaced the previous M665 model. I rode for approximately 30 miles.

    Setup: I removed my existing brakes, shortened the new hoses on the M666's about 10cm each (and swapped levers) and was ready to go out for a ride by noon. Running the rear cable is slightly more time consuming on my Soho because it partially runs through the frame. Very straightforward.

    Power: The first few stops were as powerful as my M665. The braking became increasingly more powerful as I rode, and even after just 15 miles I could easily do one-finger braking. I could never comfortably brake with one finger with the M665, and I have no doubt that with the M666 I could have locked up the front wheel using my index finger. Not sure if it's because of the metal pads or the new brakes, or both, but who cares?

    Modulation: It is very good, maybe a tad less than my M665 with resin. But this might change as the pads get more use?

    Noise: Braking is a little more noisy than with the M665 with resin, but not a problem.

    Cons: The brake levers are midgy, and although they are quite comfortable they have disturbed my normal setup so I'll need to adapt. The older M665 had nice embossed text on it (including the model number underneath). The new M666 just has text painted on it and they look cheaper. There is a rattling (cooling fins?) even on moderately bumpy road which really bugs me.

    I don't have the problem with the levers getting stuck out of reach. There is a little less resistance when pushing the levers away from the handlebars as compared to the M665, but they quite happily go back into place. Obviously I'm not doing any trails on my Soho though

    Conclusion: Overall I'm very pleased. Best I've used. Hope this is helpful.
    Last edited by jsilva; 07-30-2011 at 10:48 AM.

  2. #2
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    Just to add an update to the pad noise issue.

    I tightened the pad retaining pins a lot more and the vibration noise is almost entirely eliminated. Much happier now. Maybe Shimano sends them out with the pin very loose?

  3. #3
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    Quote Originally Posted by jsilva View Post
    Just to add an update to the pad noise issue.

    I tightened the pad retaining pins a lot more and the vibration noise is almost entirely eliminated. Much happier now. Maybe Shimano sends them out with the pin very loose?
    Thx for the tip on tighting the pins,as my xt were rattling a bit

  4. #4
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    other than the missing of free stroke adjustment, what's the difference between M666 and M785 (2012 XT)?

    the callipers look like the same and the only difference on the lever is an extra screw for the stroke adjustment.

  5. #5
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    I wonder that myself. There has to be something, perhaps better quality control? I find it hard to believe Shimano would charge so much extra for a simple screw (the SLX has the same body but with a non-adjustable screw in its place). Maybe it's just as simple as that is how this year's models have worked out?

  6. #6
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    Someone on the german board even mentioned you could probably retrofit the free stroke adjustment screw. The SLX comes with a blind screw in the hole.
    I think the real difference is the lever and it's adjustment. You can see in the pictures that SLX and XT have different levers, but the master cylinder and the calipers should be the same.
    However if the SLX levers have problems with getting out of reach, this might be enough reason to buy the XTs.

  7. #7
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    Quote Originally Posted by cscsw View Post
    other than the missing of free stroke adjustment, what's the difference between M666 and M785 (2012 XT)?

    the callipers look like the same and the only difference on the lever is an extra screw for the stroke adjustment.
    Free stroke adjustment and a forged brake lever. The forged lever would have been nice, but I didn't think it was *that* much nicer. I have an uninstalled set of 2012 slx's in my garage to install tonight.

  8. #8
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    Quote Originally Posted by necro View Post
    Free stroke adjustment and a forged brake lever. The forged lever would have been nice, but I didn't think it was *that* much nicer. I have an uninstalled set of 2012 slx's in my garage to install tonight.
    I'd be interested to know what you think of them. As I use them more I am liking them more. The braking noise has reduced further and is almost the same as my M665's with resins were. Levers feel great. It's the braking performance I've been wanting since I bought the bike.

  9. #9
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    Quote Originally Posted by jsilva View Post
    I'd be interested to know what you think of them. As I use them more I am liking them more. The braking noise has reduced further and is almost the same as my M665's with resins were. Levers feel great. It's the braking performance I've been wanting since I bought the bike.
    I'll post after getting a ride in. I also run the M665's on my singlespeed and think those are great brakes. I ride formula oro's on my trailbike, which is what I am switching out from. Like the old slx's better than the formulas.

  10. #10
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    Quote Originally Posted by jsilva View Post
    I'd be interested to know what you think of them. As I use them more I am liking them more.
    Own those for a couple months. I've tried some juicy, elixir, different older shimano (xt, xtr, some very old saints), hayes etc. These are just an another league. Lot's of guys have tried mine and everyone noticed that.

    I like everything about them so far. Will see the how they perform in conditions of cold Russian winter - already got a bottle of LHM+ fluid for them.

  11. #11
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    Any news here?

    I'm about to buy either SLX or XT. I was thinking about the Elixir R or CR, but it seems Shimano hit the nail spot on here, so I'll give them a go :-)
    I'm not sure if the free stroke adjusment is of any real use or not?
    Is the lever quality very different?
    Finally, I don't understand "lever getting out of reach" ? You can adjust the reach, yes??


    PS. Are the pads replaceable on the track with just the multitool and no pliers needed?
    The XT's seems to have a screw for pad retaining, and the SLX a split pin ??
    Last edited by NielsJ; 02-20-2012 at 12:01 AM.

  12. #12
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    The XT's threaded pin will fit the M666 calipers, you can actually see the thread where the split pins goes through, so you can retro-fit it and then you have the trail side ability to swap pads (although I've never needed to changes pads while riding).

  13. #13
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    Quote Originally Posted by NielsJ View Post
    Any news here?
    Nothing new, just continuing to enjoy the brakes I did get the pad screws because I don't like using the pins, though I haven't had to do anything with the pads since last September.

    I can't comment on the free stroke adjustment, but the unadjustable amount on the SLXs is fine for me. The "lever getting out of reach" problem has never happened to me, but someone else who reviewed the brakes had it happen to them. Though I can't imagine how unless there was something wrong with them.

  14. #14
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    What pads & rotor are people using with the M666. Wore through the original set of pads pretty much on the one run (about 3 hours in rain and gritty conditions).

    I'm looking to run a RT75 6 bolt rotor. I understand I then have the option to use met pads, G03S if that fit. Any thoughts?

  15. #15
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    Quote Originally Posted by jsilva View Post
    Just to add an update to the pad noise issue.

    I tightened the pad retaining pins a lot more and the vibration noise is almost entirely eliminated. Much happier now. Maybe Shimano sends them out with the pin very loose?
    So loose that my m666 pin actually fell out and I lost my pads on the trail. Effing Shimano! Otherwise these are fantastic.

  16. #16
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    Quote Originally Posted by jsilva View Post
    Just to add an update to the pad noise issue.

    I tightened the pad retaining pins a lot more and the vibration noise is almost entirely eliminated. Much happier now. Maybe Shimano sends them out with the pin very loose?
    It seems odd that the tightness of the retaining pin ("pad axle" on XT) should have anything to do with noise, but if it works this way, it's great! The pad axle is only in contact with one side of the caliper, so maybe it's the (loose) pin that makes the noise. If that's the case, the SLX should be noisier than the XT's, since the split pin on SLX is difficult to make tight


    Quote Originally Posted by JonathanM View Post
    So loose that my m666 pin actually fell out and I lost my pads on the trail. Effing Shimano! Otherwise these are fantastic.
    The split pin, or re-fitted the pad axle?? The pad axle has a snap ring as well. I thought it was overkill, but I guess not...??

  17. #17
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    Quote Originally Posted by NielsJ View Post
    It seems odd that the tightness of the retaining pin ("pad axle" on XT) should have anything to do with noise, but if it works this way, it's great! The pad axle is only in contact with one side of the caliper, so maybe it's the (loose) pin that makes the noise. If that's the case, the SLX should be noisier than the XT's, since the split pin on SLX is difficult to make tight




    The split pin, or re-fitted the pad axle?? The pad axle has a snap ring as well. I thought it was overkill, but I guess not...??
    I have the M666 (SLX) Calipers. They come with a split pin (or cotter pin) but I would be partial to the pad axle at this point as the split pin flew out and I lost my resin pads. Good thing is that the SLX calipers appear to have threads where a pad axle could go so I could always make that minor upgrade if I needed.

  18. #18
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    Quote Originally Posted by Kiwiplague View Post
    The XT's threaded pin will fit the M666 calipers, you can actually see the thread where the split pins goes through, so you can retro-fit it and then you have the trail side ability to swap pads (although I've never needed to changes pads while riding).
    Does anyone know where you can buy the XT threaded pin?

  19. #19
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    Some aftermarket pads come w/ the threaded bolt. SwissStop for instance

  20. #20
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    Quote Originally Posted by JonathanM View Post
    Does anyone know where you can buy the XT threaded pin?
    Your local LBS should be able to get them easily enough.

  21. #21
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    i should get some of these

  22. #22
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    XTs work better than SLX

    Quote Originally Posted by cscsw View Post
    other than the missing of free stroke adjustment, what's the difference between M666 and M785 (2012 XT)?

    the callipers look like the same and the only difference on the lever is an extra screw for the stroke adjustment.
    I've split time between 2 bikes with XT 785s over the last 3 years. Best brakes yet. Bought a new bike with SLX 675s. I thought they'd work the same, but they just didn't have the refined modulation and raw power of the XTs. I must be looney, I thought, so I rode my old bike with XT, definitely felt better. Swapped the 675 with 785 on the new bike, not a huge difference, but DEFENITELY not the same, not as good. I go 220 lbs, so maybe lighter folks won't notice so much. XT is worth the slight difference in price and different beyond cosmetics

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