Shimano GRX brake adjustment

[jannmayer]

I replaced the rotors on my Carbonda CFR707 and I cannot get the brakes to stop rubbing. I'm using Shimano GRX calipers and levers and I just put on SLX rotors. I've tried pushing the pistons all the way in and lubricating them. After I squeeze the levers a few times, the gaps between the pads and the rotors are so tight that I can't get the rotor true enough to stop rubbing. I'm having this issue with both the front and rear brake.


Is there some trick I'm missing? I tried loosening the calipers before squeezing the levers and tightening them, but that doesn't get it anywhere near close. I feel like I have the calipers centered as well as I can but the clearance on the side is so tight that the slightest bend in the rotor rubs.


I haven't had this issue with the Shimano 105 brakes on my Canyon or the basic Shimano hydraulic brakes on my mountain bike. Are GRX brakes more sensitive? Or do I have some bad calipers?

[jr223]

Its possible the brake caliper mounts are not faced perfectly and result in the caliper not being in the same plane as the rotor. It's also possible your calipers aren't retracting properly. Are they rubbing the entire way around or just in spots?

Some diagnosing:

When you try the loosen calipers -> squeeze hard -> tighten, pay close attention to what happens to the caliper as you torque it down. There should be no movement other than getting closer to the mount. If you notice any twisting or yawing as you tighten down that could be a sign.

The other thing to look at it how the rotor rubs on caliper. When it rubs is it rubbing the entire width of the rotor or just the tip? If you are sure they are true and just the edge of the rotor rubs, it may further indicate it needs to be faced.

Should be able to find a bike shop to do this for you if you think it needs to be faced.

[theo__]

You can try to open the pads with the deposit of purge installed.
If there are too much oil in the circuit, this, removes the excess.

[svanimpe]

I feel your pain. I've also found the GRX brakes are really hard to set up. There's hardly any clearance to work with
The "loosen calipers -> squeeze hard -> tighten" never worked for me, nor does using an alignment tool. That usually doesn't even fit in between the calipers and the discs.

Assuming the brake mounts are faced properly and the rotors are true, just take your time. My procedure is to slightly loosen the caliper, adjust it by hand while slowly spinning the wheel, then *slowly* tightening the calipers as you hold them into place. I've noticed that even while tightening the screws, the calipers tend to move, no matter how hard I try to keep them in their place.

I should also note that I tend to bleed the brakes until they are really tight. If you're doing the same, you could try underbleeding them (just let out a tiny bit of fluid at the caliper end), then resetting the calipers.

I'm currently waiting for an update to the GRX group. The new Di2 groups have more pad clearance, so I assume the next GRX will have it too.

[jonathanf2]

Yep GRX calipers are a real pain to align unless your brake mounts are perfectly faced. This is a trick I found which might not be the safest, but at least it will minimize rub with new pads. Anyways, first loosely tighten the bolts using the 'squeeze the lever method' to get a ballpark alignment, second release lever and loosely tighten each bolt, but only tighten one bolt to torque spec, the other bolt will be tightened under torque spec to give the caliper slight leeway in alignment. If everything works out, you shouldn't have any rubbing. Ride the bike a bit to wear down the surface brake pads and then tighten the other bolt as you get more pad clearance.

Either that or you can use fine grit sand paper to make the pads thinner! Apparently this was a big enough issue that Shimano redid the calipers to allow more clearance for the Di2 12 speed brake calipers.

[jannmayer]

Thanks for the suggestions. I will loosen the calipers and see what happens when I squeeze the lever. I did not have the mounts faced, so that is a possibility.


I can probably improve the trueness of the rotors a bit. If I still can't make any progress, I'll try bleeding a small amount of fluid.

[carbonazza]

For recalcitrant brakes, I usually put the pistons back and remove the pads.
Calipers have generally markers to center the caliper on the rotor that must be true.
Try to align the caliper with the disc(it must be as flat as possible) the best you can.
Put the pads back and brake to see what happens.

Now gnerally two problems can occur.
Either one of the piston sticks more than the other.
Or the mounts are not faced.

The first is easy. Get some silicone gel used in plumbing to assemble pipes.
Get one piston as out as you feel comfortable without popping it out.
Clean it with alcohol and apply the gel on it.
Put it back in and out a few time to lubricate everything.
Mineral oil can be used as well for the brakes that use it.

The second is easy too... if you have the facing tool.
Face the mount. Recenter the caliper, put the pad.

And ride !

[jonathanf2]

I have one more suggestion. Sometimes if your bike thru-axles are too tight, it'll cause rubbing. You can even slightly ease back on tightness (while still being adequately torqued) to give that minor gap needed to stop rubbing. You can even try fudging the wheel slightly to one side before tightening the thru-axle. I know none of these solutions sound like something needed for high end cycling equipment, but the GRX brakes have notoriously little leeway and you just want to break the pads to allow more breathing on those new pads!

[jannmayer]

I have one more suggestion. Sometimes if your bike thru-axles are too tight, it'll cause rubbing. You can even slightly ease back on tightness (while still being adequately torqued) to give that minor gap needed to stop rubbing. You can even try fudging the wheel slightly to one side before tightening the thru-axle. I know none of these solutions sound like something needed for high end cycling equipment, but the GRX brakes have notoriously little leeway and you just want to break the pads to allow more breathing on those new pads!

I will play with the axle tightness. as for the pads, they are already worn down a little bit since I didn't change them at the same time as the rotors.

[jannmayer]

For recalcitrant brakes, I usually put the pistons back and remove the pads.
Calipers have generally markers to center the caliper on the rotor that must be true.
Try to align the caliper with the disc(it must be as flat as possible) the best you can.
Put the pads back and brake to see what happens.

Now gnerally two problems can occur.
Either one of the piston sticks more than the other.
Or the mounts are not faced.

The first is easy. Get some silicone gel used in plumbing to assemble pipes.
Get one piston as out as you feel comfortable without popping it out.
Clean it with alcohol and apply the gel on it.
Put it back in and out a few time to lubricate everything.
Mineral oil can be used as well for the brakes that use it.

The second is easy too... if you have the facing tool.
Face the mount. Recenter the caliper, put the pad.

And ride !

I wasn't aware of the markings on the calipers. I will look for those and try to align with them.


I did lubricate the pistons with mineral oil but it probably wouldn't hurt to try that again. There was a lot of brake dust in that area, so maybe they are still sticking a bit.

[jonathanf2]

I forgot to ask, did you try resetting the hydraulic piston pads? I usually do this when installing new pads, but it might help in alignment as well. Also double check if your disc rotors are properly torqued to spec. Sometimes centerlock rotors can be a bit loose also causing rubbing.

I do love my hydraulic GRX brakes on my gravel bike, but it took many long frustrating nightly hours to figure out half the stuff I suggested!

[00Garza]

Wait a minute! I was ruling out chinese groupsets because supposedly shimano or sram are so much easier to set up. What gives?!!

[jannmayer]

I forgot to ask, did you try resetting the hydraulic piston pads? I usually do this when installing new pads, but it might help in alignment as well. Also double check if your disc rotors are properly torqued to spec. Sometimes centerlock rotors can be a bit loose also causing rubbing.

I do love my hydraulic GRX brakes on my gravel bike, but it took many long frustrating nightly hours to figure out half the stuff I suggested!

Yes, I did reset the pistons. I got the rotors as tight as I could but I will double check that.

[jannmayer]

Wait a minute! I was ruling out chinese groupsets because supposedly shimano or sram are so much easier to set up. What gives?!!

The shifting has been great though, especially given how far out of the Shimano specs I am!

[jonathanf2]

If all else fails, you might want to try different rotors. For example my Shimano ice rotors didn't place well with my GRX calipers, so I switched to a different rotor for my rear caliper and I was able to get that to align properly.

Wait a minute! I was ruling out chinese groupsets because supposedly shimano or sram are so much easier to set up. What gives?!!

Shimano shifters and RD/FDs are still my favorite, but GRX brake calipers are a PITA to get aligned properly due to very tight tolerances.