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  1. #1
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    XTR front disk alignment on 180mm rotor

    I mounted a new XTR disk brake on White rock solid forks, and the rotor only comes about half way or less into the brake pads. I have XTR 180mm rotor, and an XTR 180mm post mount adapter, but the caliper mounts too far out. This is the the 975, with a 180mm post adapter, not the 975P which is the post mount caliper. Has anyone else mounted the XTR on a rock solid fork? I have tried rotating the adapter every way, and it simply does not fit the 180mm rotor. What am I doing wrong?

  2. #2
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    Have you used the shims to adjust how close the caliper sits to the rotor? Do you have the caliper bolted on the right side of the adapter. I have an IS Caliper and the post mount adapter and got it to work.

  3. #3
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    Pics please
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  4. #4
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    Quote Originally Posted by NoendoinAK
    I mounted a new XTR disk brake on White rock solid forks, and the rotor only comes about half way or less into the brake pads. I have XTR 180mm rotor, and an XTR 180mm post mount adapter, but the caliper mounts too far out. This is the the 975, with a 180mm post adapter, not the 975P which is the post mount caliper. Has anyone else mounted the XTR on a rock solid fork? I have tried rotating the adapter every way, and it simply does not fit the 180mm rotor. What am I doing wrong?
    Is your fork post mount or 51mm IS and you're using an adapter? Front and rear IS adapters aren't the same, so if you are using an IS adapter make sure you have the right one (a 180mm rear adapter mounted on the front would space the caliper too far out [enough to allow a ~200mm rotor] like you are experiencing).

  5. #5
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    It sounds like you're using a post mount fork and a IS caliper with an adapter. Could it be that your post mount is not a 160mm post mount?

    If you have pictures, it would help a lot.

  6. #6
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    Quote Originally Posted by anotherbrian
    Is your fork post mount or 51mm IS and you're using an adapter? Front and rear IS adapters aren't the same, so if you are using an IS adapter make sure you have the right one (a 180mm rear adapter mounted on the front would space the caliper too far out [enough to allow a ~200mm rotor] like you are experiencing).
    I have attached a photo that shows the adapter, mount, and 180mm rotor. You can also see in this photo where the rotor enters the caliper. The model number is SM-MA-F180S/P, which I believe is a front.
    Attached Images Attached Images

  7. #7
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    Here is a picture that is not quite so close in, so you can see the fork mount.
    Attached Images Attached Images

  8. #8
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    It looks like your fork is for 180mm. Adaptor adds another 20mm. Since there's no adaptors that can mount an IS caliper on a post mount that doesn't increase rotor size, you're gonna have to get a 203mm rotor.... or a new fork.... or a PM caliper. All pretty expensive solutions, sry you're SOL. I hate PM

  9. #9
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    That's a rear caliper. Notice the extra long mounting "arm" on the bottom? The front caliper has a short "arm" just like the top.

  10. #10
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    good catch. y didn't i think of that. if you're lucky you've got the calipers swapped

  11. #11
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    The two calipers I was shipped are identical. The only marking on the back of each one is BR-M975 and F180. If they shipped me two rears, I should be able to swap one out for a front. The F180 doesn't mean it is a front, does it? I can't find photos and models on the Shimano site. I'd like to know exactly what I have so I can tell the shop what I need. Thanks for your help!

  12. #12
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    The F180 means that if it WAS used for the front in an IS scenario (no post mount adapter), it would be a "180".
    Last edited by the-one1; 04-19-2009 at 01:08 PM.

  13. #13
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    Quote Originally Posted by NoendoinAK
    The two calipers I was shipped are identical. The only marking on the back of each one is BR-M975 and F180. If they shipped me two rears, I should be able to swap one out for a front. The F180 doesn't mean it is a front, does it? I can't find photos and models on the Shimano site. I'd like to know exactly what I have so I can tell the shop what I need. Thanks for your help!
    Tell the shop you want a post mount caliper front and rear ,forget the I.S. there a drag to adjust...

  14. #14
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    Quote Originally Posted by the-one1
    The F180 means that if it WAS used for the front in an IS scenario (no post mount adapter), it would be a "180".
    like my grimeca

  15. #15
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    both calipers are the same front and rear its the lenght of the hose thats not, thats is why they mark it front for short hose rear for longer hose, IS to post PM with 180 adaptor will accomodate 8" rotor,just use standard adaptor for 160 IS to PM and your 180rotor will be just fine, if the pad contact is not perfect use shims to align it.

  16. #16
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    Did it end up being two rear calipers? How did you solve this? I'm looking at doing the same thing with my IS m975 and a PM Fox fork and 180mm rotor, but I haven't ordered the adapter yet. I hope I don't run into the same issue as you.
    Wanted: Ritchey P-20,21,22,23 in Team colors, 18-inch, '92-99, Ritchey Logic fork (threadless); NEW Rock Shox Judy Decal Sets

  17. #17
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    Quote Originally Posted by ferdie f
    both calipers are the same front and rear ...
    I don't think that's true.

    If you look at the Shimano site it has different technical drawings for the front (http://techdocs.shimano.com/media/te...9830609100.pdf) and the rear (http://techdocs.shimano.com/media/te...830609101.pdf). The rear looks like other IS mounted rear calipers and has a longer arm than the front.

    Tim

  18. #18
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    Quote Originally Posted by Wombat
    I don't think that's true.

    If you look at the Shimano site it has different technical drawings for the front (http://techdocs.shimano.com/media/te...9830609100.pdf) and the rear (http://techdocs.shimano.com/media/te...830609101.pdf). The rear looks like other IS mounted rear calipers and has a longer arm than the front.

    Tim
    Correct. Front an rear calipers are different in this case for this caliper. You can use the rear caliper in the front if you upsize the rotor to 180 from 160.

  19. #19
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    Yup, you guys are right. I checked my XTR's this morning and the rear has a longer arm.
    Wanted: Ritchey P-20,21,22,23 in Team colors, 18-inch, '92-99, Ritchey Logic fork (threadless); NEW Rock Shox Judy Decal Sets

  20. #20
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    Quote Originally Posted by bryanus
    Did it end up being two rear calipers? How did you solve this? I'm looking at doing the same thing with my IS m975 and a PM Fox fork and 180mm rotor, but I haven't ordered the adapter yet. I hope I don't run into the same issue as you.
    IS caliper to PM pork will fit 180mm to 203mm rotors only, some PM fork make for standard 203 rotor to elliminate adaptor, make sure your fork is standard 160 PM fork order an IS to PM adaptor and it will solve the problem. XTR now offers IS & PM caliper, The PM caliper is better than IS caliper you dont need shims to allign the caliper rotor.
    Last edited by ferdie f; 06-17-2009 at 04:56 PM.

  21. #21
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    Yes, my issue ended up being that I had a caliper for a 160mm front or 140mm rear (although this same caliper fits my 160mm rear without an adapter). The caliper for a 180mm front or 160mm rear, with a 180mm post mount adapter, fit fine.

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