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  1. #1
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    Rotor rub - XTR Trail w/180 XT ICE Rotor

    I've got a few rides on my new build but I'm experiencing rotor rub up front. I'm running XTR trail to a 180 XT ICE rotor, mounted to the correct Shimano extension post. Rotors are correctly mounted to my I9 Enduro hubs.

    I've tried everything I know, nothing seems to work:

    - Losen caliper and press lever to clamp onto rotor, then tighten caliper down.
    - Taken pad out to make sure pistons are flush.
    - Taken my time to very carefully set caliper by hand, using my eye and a rotating wheel to make sure I had no rotor rub. Then tightened to spec.

    Bottom line, I can eliminate the rub in my garage but as soon as I hit the rough stuff, the rub comes back.

    What am I missing? There must be something I've yet to try.

    Thanks!

  2. #2
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    Do you remove your wheel between home and the ride? I know that sometimes no matter how much you get them aligned, once you remove the wheel, bang, out goes all the hard work.
    Are the threads in the mounts clean? Bolts done up to correct tightness?

  3. #3
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    valid ideas. i live where i ride, so the wheel always stays on. i use a torque wrench, tightness is perfect.

    hmm, i've never cleaned the threads -- i'll look into that. i will say, when i tighten down, i definitely get some caliper drift. i figured it was due to the bolt washer turning and moving the assembly. i may need to really grease it all up super good and try again.

    thanks

  4. #4
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    I wouldn't grease anything regarding your brake mounts. Definitely make sure the caliper mounting bolts have loctite, and when tightening the bolts to torque spec do so VERY gradually, alternating between mounting bolts until both are torqued. It helps to hold the caliper firm while tightening the bolts, since you noticed that you get some drift (I definitely see this happen with my XT brakes). After setting mine up this way, the alignment seems to have stayed the same since... Also if your using normal QR skewers, rest the bike on the ground with the wheel loose in the dropouts and put downward pressure on the bike (push on the stem, or seat depending on which wheel your tightening), then tighten up the skewers snug. This helped me before when I used standard QR's.

    Another thing I noticed (using ICE tech rotors), is that after thoroughly breaking in the brakes my rotors warped slightly, but just enough to cause a little rubbing. I took a shot at truing them and made enough of an improvement to get rid of the rubbing, and they seem to have stayed true since... Maybe its an effect of the break in process.

    After getting everything squared away, I couldn't be happier with the newer shimano's!
    "That's a niiiiiiiice biiike boy! That a Huffy!?"

  5. #5
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    it's funny, i wrote about the grease and then realized how dumb that would be. the last thing i want is movement on the caliper and grease would certainly encourage that.

    when i torque things down, it took forever. i alternated bolts, went SUPER slow and set the caliper perfectly before my ride. zero rub. during my climb and the first part of my ride is was fine but when i hit the big bumps, the rub came back with a vengeance.

    maybe you're right, maybe the rotor got out of true somehow. i've never trued a rotor but i guess i should look into it.

  6. #6
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    When you aligned the brake rotor was it right at the edge of the L/R adjustment allowed by the brake caliper? On my bike with a Hope Pro II front hub, 2011 Fox F100 Terralogic 15QR fork , 180mm Shimano RT86 Ice Tech rotor, Shimano post mount adapter and Shimano M988 XTR Trail caliper I had to shim the brake rotor outwards in order to make the rotor line up properly.

    I've found that my Shimano RT86 180mm Ice Tech rotor is quite soft. It needs truing fairly regularly as the rotor seems to warp easily. It doesn't take much effort to bend back into shape though. If the rotor is running very close to one of the brake pads (which will seem to work ok at home) when you get mud and dirt on the rotor it will become noisy and rub until it cleans itself up again. If you're on a muddy track with constant spray onto the bike it means the brakes are going to rub all the time. The solution being to get the rotor further away from the brake pads.

    Brake rotor truing
    Disk Brake Rotor Precision Truing

    The other thing that I've found with my front M988 XTR Trail brake is that it tends to pump up a bit if I'm on the brakes for more than a few seconds. If I have to drag the brakes all the way down a descent you can hear the front brake rotor rubbing afterwards for a few minutes.

    Love the new 2012 XT brakes

    .

  7. #7
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    Good stuff, thanks.

    Truing the disc seems like a pain -- is it as difficult as it looks?

    I think you're right about how the brakes pumps up a little if you stay on it for a while. I've noticed that the pistons stick out a like 1/16 or even 1/8 if I pull the pads after a ride and look in. To set them back, I let out the little screw on the lever reservoir and push back in the pistons. But it doesn't seem to last. This said though, I doubt that the pistons only sticking out that far would create rotor rub. I think it's the rotor being out of true -- because the rub isn't constant -- there are hot spots.

    While I totally am amazed by the breaking power of the Trails -- this ICE rotor thing could be a little bit of a problem. For what it's worth though, my rear 160 is perfect. Hmm, I wonder if the larger 180 just isn't as strong because of it's larger diameter?

  8. #8
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    Could be the mineral oil heats up while you ride and pushes the pistons toward each other. Maybe take out excess or re-bleed?

  9. #9
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    Quote Originally Posted by wyolink View Post
    Hmm, I wonder if the larger 180 just isn't as strong because of it's larger diameter?
    The larger the disc the greater the braking force. It is always easier to lock up your rear compared to the front though, so the perception is that the rear is stronger.
    I have RT98 rotors and I've never had them go out of true, even after a couple of offs, are they really that soft? Truing discs is usually quite straight forward though, you can buy rotor truing tools from your lbs for a minimal cost.
    Shimano's free stroke adjustment is notorious for not doing much though, so might not be much point with you playing around with it.

  10. #10
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    Truing a brake rotor is quite easy, unless you're aiming for perfection when you need to use a gauge. If you're just straightening it a bit then you can do it by eye using a single truing tool (eg: Morningstar or Park) and the brake caliper. At a push you can use an adjustable spanner but a longer tool is better so you don't damage the rotor.

    Park Tool Co. DT-2 : Rotor Truing Fork : Brake Tools

    Spin the wheel and at the sections where the rotor is out of true gently bend the rotor in the opposite direction. Only do this on the supported spoke sections of the brake rotor as you'll put a kink in the rotor bending the thinnest sections. Gently repeat until the rotor spins without rubbing.

    My previous 183mm Hope floating rotor hardly ever needed touching but this 180mm Shimano RT86 front rotor has needed tweaking a few times now. What's notable is how little effort it takes to bend it. A gentle push on the Shimano RT86 rotor is all that's needed to bend it back to being true again.

  11. #11
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    maybe the pad that touches the rotor is not at 12&6o'clock when brake is appllied, it touches first the upper part or the lower part left and right of the pads, this is what cps do like avid uses with their caliper the pads and rotor are always parallel. avid are the only brand that use this and its good. for shimano what i do is make the standard procedure to allign discbrake - i put it in the bike stand then i remove the wheel insert a ruler to the caliper press lever holding by a toe starp or rubberband and look at the allignment of the ruller you insert to the caliper see if the ruler is at 12&6 o'clock looking from the rear if not file some part of the adaptor that the caliper rest to make it at 12&6o'clock in this way it will make more clearance and pads alway parallel to the rotor do the allignment procedure again,best if you have new pads, if post mount file some part of the caliper, i hope this will help.
    Last edited by ferdie f; 01-08-2012 at 01:48 AM.

  12. #12
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    I am not sure what 'cps' is from what ferdie f said but if you mean the concave/convex washers, then that is what I would recommend as well. I had the same problem and used them off an Avid set and the rubbing became a non issue. It allows you to modulate the caliper by up to 8 degrees I believe. However, I need to go to the hardware store and get a lower profile washer so the pad can brake on more of the rotor. Good luck

  13. #13
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    Does the Ice-tec rotor RT86 work with non series Shimano calipers? Like an M446 Shimano caliper i.e. This is because I've seen an RT76 rotor around as well and they are a lot easier to find than the Avid rotors.

  14. #14
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    yes kaneshiro76 i think so, as long as you are using the right adaptor. avid185, hope183,shimano180. diff rotor size needs different adaptor.

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