REVIEWS DEALS BIKESHOPS TRAILS

Adapter / Rotor contact position question XTR Trail

6963 Views 31 Replies 8 Participants Last post by PissedOffCil, Mar 8, 2011

DanielM3

Discussion Starter · Mar 4, 2011

Does this look correct? I think that the caliper position is too high.

I have a anthem 29 that has a post mount rear. I went with 180mm shimano set up and have the shimano 180mm post mount adapter. All looks well in the front but the rear looks incorrect.

Anyone seen this before? Is the answer to have material machined off of the rear adapter?

Thanks for any info

Daniel

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1 - 20 of 32 Posts

Squash

· #2 · Mar 5, 2011

Nope that's not correct. Your caliper appears to be about 10mm or so to high.

What is the Shimano part number on the adapter that you are currently using on the rear? If it has an F in the number you've got a front adapter on the rear, example SM-MA-F180PPA. That number is for a front 180mm post mount brake to post mount fork adapter. The F in the part number designates a FRONT adapter. A rear adapter would have a part number like SM-SA-R180PPA, or something similar.

If that's the case, the answer is not having material machined off the adapter, but getting the correct adapter! However that might be an interesting exercise. I am not currently aware of anyone that carries a 180 pm to pm rear adapter, or if Shimano even makes one yet. Post mount frames are not that common, and it usually takes a bit of time for brake manufacturers to catch up with something new like that.

With most post mount frames the mounts are designed for a 160mm rotor and a direct mount of the caliper to the posts. This is the case with the Anthem. Since 180 rear PM to PM adapters are rather rare at the moment, I would suggest contacting Giant seeing what they recommend. Either that or contacting Shimano and finding out if the do indeed make a 180 PM to PM adapter for their brakes.

This is all assuming that you're rear brake caliper is indeed a post mount caliper. A picture of the caliper with the wheel installed would help a bit.

Good Dirt

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shiggy

· #3 · Mar 5, 2011

Squash said:
Nope that's not correct. Your caliper appears to be about 10mm or so to high.

What is the Shimano part number on the adapter that you are currently using on the rear? If it has an F in the number you've got a front adapter on the rear, example SM-MA-F180PPA. That number is for a front 180mm post mount brake to post mount fork adapter. The F in the part number designates a FRONT adapter. A rear adapter would have a part number like SM-SA-R180PPA, or something similar.

If that's the case, the answer is not having material machined off the adapter, but getting the correct adapter! However that might be an interesting exercise. I am not currently aware of anyone that carries a 180 pm to pm rear adapter, or if Shimano even makes one yet. Post mount frames are not that common, and it usually takes a bit of time for brake manufacturers to catch up with something new like that.

With most post mount frames the mounts are designed for a 160mm rotor and a direct mount of the caliper to the posts. This is the case with the Anthem. Since 180 rear PM to PM adapters are rather rare at the moment, I would suggest contacting Giant seeing what they recommend. Either that or contacting Shimano and finding out if the do indeed make a 180 PM to PM adapter for their brakes.

This is all assuming that you're rear brake caliper is indeed a post mount caliper. A picture of the caliper with the wheel installed would help a bit.

Good Dirt

There is no difference is the radial spacing of front and rear post mount so the same mounting brackets are used for larger rotors.

Daniel, might you have the bracket on backwards?

DanielM3

Discussion Starter · #4 · Mar 5, 2011

Thanks for the detailed replies. Like all the replies though that I have been getting there is conflict though.

Here is a picture but it is an older one when it had stock brakes.

My dealer called Shimano and they were largely unsure about post mount rear set up. They said that they did not make a rear post mount set up and asked to try the front, which I have already but is not correct.

I tried the adapter both directions and that is not the issue. The arrow is facing forward and I am using SM MA F180P/ P2 i believe the model is. This is the post mount front adapter.

I do not think that the correct adapter is available and may have to just go with a 160mm rear rotor?

Not sure of my other options. My dealer did not either and suggested the machining route but that was to just help when no correct options where there.

Thanks,
Daniel

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Trevorken

· #5 · Mar 5, 2011

I presume that you are still using the same hardware as on the original brake.
You have to mount the calliper straight onto the adapter, without using those "conical" things (sorry, I can't remember the name) below it.
These should only be used with avid brakes.

shiggy

· #6 · Mar 5, 2011

DanielM3 said:
Thanks for the detailed replies. Like all the replies though that I have been getting there is conflict though.

Here is a picture but it is an older one when it had stock brakes.

My dealer called Shimano and they were largely unsure about post mount rear set up. They said that they did not make a rear post mount set up and asked to try the front, which I have already but is not correct.

I tried the adapter both directions and that is not the issue. The arrow is facing forward and I am using SM MA F180P/ P2 i believe the model is. This is the post mount front adapter.

I do not think that the correct adapter is available and may have to just go with a 160mm rear rotor?

Not sure of my other options. My dealer did not either and suggested the machining route but that was to just help when no correct options where there.

Thanks,
Daniel

If the caliper lines up with the 160mm setup, it has to work with the 180, too. The parts used for post mount are identical front and rear. Zero difference.

Did you use the Avid CPS washers with the Shimano brake? (you should not) that would move the caliper up on the rotor about as much as you show.

DanielM3

Discussion Starter · #7 · Mar 5, 2011

No avid hardware is used.

The stack is...frame/adapter/caliper/2 shimano washers then bolt. Nothing to space it up incorrectly.

It is not the correct part i am nearly 100% certain????

shiggy

· #8 · Mar 5, 2011

DanielM3 said:
No avid hardware is used.

The stack is...frame/adapter/caliper/2 shimano washers then bolt. Nothing to space it up incorrectly.

It is not the correct part i am nearly 100% certain????

Take the 180mm bracket off the front and put it on the back.

The brackets are the same for front and rear. There is no other post mount spec. Nothing different about the Giant frame or the 160 rotor would not have worked either.

DanielM3

Discussion Starter · #9 · Mar 6, 2011 (Edited)

So here is the image of the 160mm rotor.

It looks like it may be slightly high but no where near as off as the 180 set up.

Thoughts? Look too high still?

Thanks for all the replies, I really appreciate it

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shiggy

· #10 · Mar 6, 2011

DanielM3 said:
So here is the image of the 160mm rotor.

It looks like it may be slightly high but no where near as off as the 180 set up.

Thoughts? Look too high still?

Thanks for all the replies, I really appreciate it

As long as the pads do not hang off the outside edge of the rotor it is fine.

DanielM3

Discussion Starter · #11 · Mar 7, 2011

So I still do not know what to do. I really do not understand it and tend to thing the original reply is correct and I need a Rear adapter..which is not made??

411898

· #12 · Mar 7, 2011

The adapter shown on the Shimano website for XTR race/trail for 180 is:

part# SM-MA90-R180P/S (REAR!)

There are DIFFERENT adapters indeed for front and rear!

The part# is the same but there is an "F" in front of the "180" for the FRONT adapter AND a "R" in front of "180" for the REAR adapter.

Here's the front and rear PDFs....see for yourself!

Front Brake: http://bike.shimano.com/media/techd...R/EV-BR-M985-F-3075_v1_m56577569830715115.pdf

Rear Brake: http://bike.shimano.com/media/techd...R/EV-BR-M985-R-3076_v1_m56577569830715116.pdf

SHIGGY IS WRONG, LOL!

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DanielM3

Discussion Starter · #13 · Mar 7, 2011

Yeah I have seen that but the SM-MA90-R180P/S is for a post to IS. I am going post to post so would need something like SM MA R180P/ P? Does that exist?

411898

· #14 · Mar 7, 2011

DanielM3 said:
Yeah I have seen that but the SM-MA90-R180P/S is for a post to IS. I am going post to post so would need something like SM MA R180P/ P? Does that exist?

Yup you're right ...I'M WRONG!

Did you try flipping the adapter around as suggested?

SHIGGY IS CORRECT, LOL!!! (sort of...there obviously needs to be a different 180 rear adapter in this case)

411898

· #15 · Mar 7, 2011

It' too bad the positioning slots in the caliper were not positioned to allow for the caliper to be slid forward or backward instead of just side to side...

Also check to see if there is enough clearance to possibly machine the adapter down a bit to lower the caliper position when mounted.

According to Shimano, a rear PM adapter is not available. The PM mount shown in the PDF is clearly coded "F" for "front". This would leave me to believe that a rear adapter would be different. Yet, Shiggy has a point, the position of the PM mounts on the frame should be just like the position of them on a fork.

I'd machine it down (if there would be enough clearance so that the caliper didn't contact the adapter) if it was me...

Otherwise, create your own adapter OR try a different brand PM 180 mount.

Easier still, drop to a 160mm disc and forget about your rear adapter woes....

DanielM3

Discussion Starter · #16 · Mar 7, 2011

I have tried the mount in both directions. When it is the other way around the inside top of the caliper hits the rotor.

I did get a 160mm rotor and have a picture of it mounted above. It mounts properly (may be a little off but I suppose I am getting picky there..)

Just a bummer that I can not figure this one out.

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Daz_1983

· #17 · Mar 7, 2011

I think the shimano pads are a little narrower than what most other brands use in there brakes. My Deore M595's uses the same pads i believe, My contact patch with the rotor is similar to yours on the front and rear rotors, the outer edge of the pad is in contact with the rotor though so all is fine.

I'd be a little concerned if the pad over shot the rotor though.

411898

· #18 · Mar 7, 2011

DanielM3 said:
I have tried the mount in both directions. When it is the other way around the inside top of the caliper hits the rotor.

I did get a 160mm rotor and have a picture of it mounted above. It mounts properly (may be a little off but I suppose I am getting picky there..)

Just a bummer that I can not figure this one out.

The fact that the caliper sits a little high on the 160 rotor indicates an error in PM mount positioning when it was welded to the frame. Sad to say but I have to assume that any brake caliper is going to ride high mounted there. Scream like Hell at the bike frame company. You've certainly got the proof in pictures to back up your troubles. I think they should replace your frame!

Daz_1983

· #19 · Mar 7, 2011

ambassadorhawg said:
The fact that the caliper sits a little high on the 160 rotor indicates an error in PM mount positioning when it was welded to the frame. Sad to say but I have to assume that any brake caliper is going to ride high mounted there. Scream like Hell at the bike frame company. You've certainly got the proof in pictures to back up your troubles. I think they should replace your frame!

If that was the case then the original Avid caliper would have had the same issue, but it didn't.

As my previous post, i think it's just down to the shimano pad being narrower than the avid pads, and the Shimano rotor as been manufactored to suit other brands of caliper/pad size, which would make sense. As long as the pad isn't over shooting the rotor then you've got no problems.

411898

· #20 · Mar 7, 2011

Daz_1983 said:
If that was the case then the original Avid caliper would have had the same issue, but it didn't.

As my previous post, i think it's just down to the shimano pad being narrower than the avid pads, and the Shimano rotor as been manufactored to suit other brands of caliper/pad size, which would make sense. As long as the pad isn't over shooting the rotor then you've got no problems.

The pad positioning over the rear 180 rotor as shown in the picture supplied looks like it overhangs the top of the rotor to me! Not good!

It simply can't work perfectly on the front and then not on the rear, that's a frame mount positioning issue.

Hey DanieIM3, post pics at angle that shows the positioning of pads over the rear 180 rotor, looking through the caliper from behind. Use a flashlight so that we can see it clearly.

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