XTR Rear Brake Loses Center

[Thrawn]

From day 1, the rear brake has been rubbing the rotor during a ride. I center the pads before every ride, but it ends up rubbing after finishing a quick section. Once, I even set it up so that there was a huge pad gap with a squishy brake lever. Still ended up rubbing later in the ride. What's causing this? Are the pads not retracting? Frozen piston? Something from when the brakes heat up?

Bike is a hardtail. It's a new build with about 9 rides. Brakes were bled and pads were centered using feeler gauges. Current XTR with 160mm rotor, 6-bolt, and IS adapter.

[the-one1]

Is the caliper centered over the rotor?

[Motivated]

I think your rotor is warping.

[Thrawn]

Yes... Caliper is centered... There is a slight warp to the rotor, but it hasn't changed... even with the pads open to the max, they found a way to rub after riding...

Gonna see what happens when I ride without using the rear brakes... Just to eliminate the mounting bolts from loosening... It was on there gorilla tight last time... we'll see...

Anyone ever have their piston freeze? Maybe the pad it not retractingas after they heat up...

[AlexRandall]

Usually a sticky pad. Disc brakes are pretty finicky sometimes.

Remove the pads, give the lever a small squeeze and drop some light lube around both pistons, focusing on the one that moves less. Us a large flat head screwdriver, crescent wrench or similar to push the pistons back to flush with the body and repeat 4-5 times. The more reticent pad should be moving much more freely now.

[scottap2003]

I'd be more specific about the lube part of that. Shimano recommends only using their mineral oil to lube the pistons. They claim that some other types can leak back into the system, which is what some of them are designed to do is to get into all the little nooks and crannies. But, like Alex said, allow the pistons to come out a ways, lube them with mineral oil, push em back, and repeat a few times.

[Thrawn]

Thank you Alex and Scott! I will try that. Hope it does the trick... Must be sticking after it heat cycles...

[Thrawn]

Lubricating the pistons seem to have worked. Unfortunately, I got air in the system somehow. I found mineral oil leaking from the bleed port. Not a lot though. Just enough to fill the rubber cap. Guess I need to bleed. What caused this? Too much pumping on the levers without the pads installed?

[petercarm]

Guess I need to bleed. What caused this?

Bleeding with the pistons extended and then forcing them back. .. The fluid has found a path of last resistance.

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[Thrawn]

Brakes bled and was finally able to go on a ride... Brakes remained centered the whole time... No more post ride rubbing... Thanks everyone...

[SHIFTY1]

I just got my xt's....having the same issue...

[Wheelman55]

If it's all new...brakes, rotors, pads...double check your clearance with a flashlight...used as a backlight it'll show any clearance issues in your setup.