Any tips on centering Shimano's flat mount disc brake calipers?

Especially for light weight issues concerning cyclocross / touring bikes & parts.

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ms6073
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by ms6073

Shimano XTR M9000 post mount calipers were so easy to get centered. Loosen the mounting bolts, assure the caliper moves freely, squeeze brake lever, tighten bolts, alternating to ensure even torque, viola, caliper centered and no rotor rub. My KTM Revelator Sky disc with flat mounts has been a continual exercise in futility, as I loosen the caliper, verify caliper moves/centers, squeeze the front lever, but as soon as I apply more than ~4nm torque to the mounting bolts, the caliper appears to cant and skew off center, resulting in the rotor rubbing the outboard pad. :unbelievable:
Michael - The Anaerobic Threshold is neither...

by Weenie


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Fixie82
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by Fixie82

My tip with flat mounts is to position a light above or below the caliper shining directly on to the caliper so it illuminates each side of the pads. It gets awkward but loosen the bolts just enough that the caliper will move with pressure, not so loose that it will move freely. Manually move the caliper in or out from each end until the rotor runs freely.

The shadows from the light source will help you see how much space is on each side. It sounds fiddly and it's not as easy as the old squeeze the lever and tighten but it's not too bad.

Of course this assumes your rotors are not warped.

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ms6073
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by ms6073

Thanks. Working brand new Shimano BR-RS805 brake calipers and RT99 Freeza 140mm rotors, so not likely they are warped.
Michael - The Anaerobic Threshold is neither...

TheKaiser
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by TheKaiser

I haven't worked on a flat mount bike yet so I haven't studied the interface closely. What seems to be keeping the caliper from holding position when you just squeeze the rotor and tighten the bolts as you would on a post mount? Does it tend to creep out of place as the bolts are tightened?

I have seen cases of post mounts where the mount is not properly faced, and they would creep or twist when tightened. There are tools available to face them properly, but I am not sure if the same type of thing is available for a flat mount, or of the position of the mount would make that impractical.

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ms6073
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by ms6073

Yes, caliper creeps as bolt torque is finalized. I was also thinking the mounts need to be faced and Park Tools has the toolset for the job but that is such a niche task, may check with local shop that specializes in MTB to see of they can face the mounts.
Michael - The Anaerobic Threshold is neither...

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nycebo
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by nycebo

Fixie82 wrote:...loosen the bolts just enough that the caliper will move with pressure, not so loose that it will move freely. Manually move the caliper in or out from each end until the rotor runs freely.


This. It's exactly how I got my calipers perfectly centered. Now occasionally with wear, you might hear the hint of a very very very light drag, but it's usually resolved with one FIRM stop (but not completely).

Good luck with the brakes. I use the exact same setup and am IN LOVE. One-finger, semi-on-the-lever to a complete and instant emergency stop the other day when a car pulled into my lane from a driveway without looking. Never could do that with my old Dura 7900 brakes.

TLa
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by TLa

ms6073 wrote:
Tue Sep 20, 2016 12:35 pm
Yes, caliper creeps as bolt torque is finalized. I was also thinking the mounts need to be faced and Park Tools has the toolset for the job but that is such a niche task, may check with local shop that specializes in MTB to see of they can face the mounts.
Did you get it fixed?

I have the same problem with my frame (not really keen on spending 500€ for the Parktool)

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Miller
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by Miller

I wonder if the caliper moves because the washer under the caliper bolt head rotates with the bolt and thus moves against the caliper body. Maybe adding another washer could mitigate this?

ooo
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by ooo

Peter Verdone offers news design for frame integration:

http://www.peterverdone.com/pvd-fm140-variant/
Peter Verdone wrote:Another post in the never ending saga of the new FM140 mount I’ve been working on.

I decided to go with a special variant to work better with SRAM calipers. SRAM calipers are shifted about 0.3mm outboard. Along with some manufacturing, paint, and tooling tolerances, the 1.omm slot from reference is quickly used up setting up the caliper. Many builders have been experiencing this issue.

I give an extra 0.5mm of room on the outboard side and is shy of the SRAM and Shimano specification on the inboard side. The slot is 3.0mm overal and should work a lot better in real life.
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by Weenie


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