mb04042

After spending an obscene number of hours reading and trying to fix front disc brake rubbing, hoping someone can help me:

I can get the front brake to not rub through manually adjusting the caliper position. But as soon I do a medium or hard brake it starts rubbing. And keeps rubbing. Until I unscrew the caliper bolts, manually adjust position and re-tighten again. But same experience at next braking. Have gone through this at least 50 times, feel that stuck in unchanging infinite loop. Super frustrated.

My theory is that the caliper is moving when brake hard, and then never returns to original position. But I have tightened bolts with a lot of force on some of these attempts. I have read the sticky piston issue, but I don’t think that is it because it feels like I am re-shifting caliper back into same position each time, and they are new brakes so hoping not sticky out of box.

One concern I have is that the top bolt is quite long and has an interesting set of 5 washer type things (not sure correct term, wish I could post photo). This is what came with the bike (Canyon AL 5.9, with similar Shimano brakes). Wondering if that stack of washers is normal, if any possibility that is creating a small amount of room for caliper to shift. If we weren't in current quarantine situation I would head to store try to get help finding a bolt that was different length to try with fewer washers. But no possibility to easily do at moment.

They are nearly brand new Shimano Deore brakes. Have about 100km on them. With good amount of descending included, so hoping I am past any break in period excuses.

Many, many thanks if anyone has an idea? Feel like I have read hundreds of posts on disc brake rubbing, and tried suggestions. But haven’t found exact same situation.

dsbrantjr

It also sounds to me like the caliper is moving. Have you used a torque wrench and applied the manufacturer-recommended torque? If you are using an L-wrench or (ick!) multi-tool you may not be applying sufficient torque.

alo

I had a situation where, after hitting the brakes hard, they would lock on. The only way to release them was to move the bike in reverse. This was dangerous, for example, if I had to stop suddenly in the middle of an intersection. I suspect it might be a design fault with those particular calipers.

I replaced calipers and pads.

On my bike, everything to do with the gears is Shimano. The brakes may or may not have been Shimano.

dsaul

There should not be more than 1 washer under the head of the mounting bolt. SRAM used to use CPS(caliper positioning system) washers under the caliper, but I don't think any brand uses those anymore.

bikeme

When you are "manually adjusting the position", are you doing so by loosening the bolts then squeezing the brake lever and holding it tight to let the caliper self-center, then tightening the bolts, releasing the lever afterward? Or are you trying to eyeball the centering?

bikeme

My Deore XT M8000s have a dished, conical, and a flat. 5 seems extreme and would cause slop, I'd think.

bikeme

The torque is only 6nM to 8nM.

Trevtassie

Centering disc brakes is the new adjusting post mount brake pads!

Anyhoo, it shouldn't have the washer stack. Not even according to the Shimano parts diagram. Pretty well the only disc brakes that have and need those are single piston mechanical calipers (don't know of any single piston hydraulic calipers), they are there to correct the uneven wear caused by the single moving pad distorting the disc. Any twin piston caliper doesn't need them. If I had to guess I'd say somebody either replaced mechanical brakes with hydraulic and left the washers on there or lost the top bolt and reused an old one. Theoretically if all the washers were on the top of the caliper under the bolt head it shouldn't matter.
One thing to try would be to use something like two 0.5mm feeler gauges between the pads and the disc while you tighten the bolts to space them out. Like the Hayes brake caliper centering tool does.

Trevtassie

Oh and another thing to check... make sure the axle is really tight. The pictures I looked at of the canyon show a QR front axle. If it's an external cam skewer, replace it with an internal cam one like a Shimano and do it up good and tight with the wheel bedded into the drop outs. If it's a through axle, make sure it's tight.

SalsaShark

One more thing to check is to make sure the lock nut and cone on your hub has not worked loose. Any amount of slop in your hub will be transferred as side to side play up through the radius of the wheel and also the brake rotors. Have seen this cause similar centering issues on rim brakes, but could also cause a problem to a lesser degree on disc brakes.

mb04042

Thanks all. It does seem to have been caliper moving. Tightened bolts extremely hard and no rubbing after a few rides. But appreciate the confirmation above that 5 washers might be contributing (that is what came from Canyon) - planning to replace that setup at next moment it falls out of this good equilibrium; too scared to touch anything now. And going to watch axle more closely next time as well.

But yes it was manual eyeballing adjustment - which was super hard because as put big torque on the bolts it would move slightly. I tried the squeeze brake method many times, but zero luck. And correct that there was some use of a multitool. Still I was tightening pretty hard. I didn't recall from the days when I used a good torque wrench that 8Nm is that much effort. But found a cheap torque wrench sitting around and used that. Such bad quality wrench that I am skeptical on its precision - so much effort (or I have just gotten weak) that was worried would strip bolt head. Ordering a good torque wrench. But anyway is working now - no rubbing after hard braking.

(And for any newbies stumbling across this with disc brake rubbing problems, stating the obvious but to hopefully save someone from insane amount of time: check that it is actually the rotor rubbing the brake pads. I spent an absurd amount of time making adjustments on unpredictable "pad rubbing" noise. Eventually discovered that it had nothing to do with pads. Somehow the plastic dork disk thing was brushing up against a spoke in a way that had convinced me I had warped rotor or something.)

Many thanks again for the help, really appreciate it!