2

so these are Shimano saint hydraulic disk brakes and i took the wheel off the other day to clean it, put it back on, and for some reason the pads are rubbing overly hard (without actually pulling the brake lever. So the front wheel wont spin too well, ive had another couple of rides with it, but is stil the same... the pads are rubbing too hard.

3
  • 2
  • 2
    Nearly 100% of the time, this happens because someone squeezed the lever while the wheel was out. Reset the caliper and try again. You can use a broad clean screwdriver if you are careful, but the proper tool is better.
    – JoeK
    Mar 3 at 21:57
  • 1
    Late addition, but I believe the proper tool is called a piston press.
    – Weiwen Ng
    Apr 2 at 15:57
1

The wheel might just be inserted slightly differently than it was before. That happens especially with quick release skewers. With thru axles the wheel insertion is more consistent.

Try to open the wheel, wiggle it a bit and close it again and see of the position changes. You might get it aligned well.

If it does not help, you may need to re-align your brake calipers.

1
  • okay thanks ill try it and see if that works! Mar 3 at 12:43
1

First thing I would check is that your wheel is fully seated and centered in the fork's dropouts. If you've confirmed correct wheel alignment, move on to the brake caliper. Shimano hydraulic brakes auto-compensate for pad and rotor wear by the pistons moving out from the caliper so they essentially obtain a new baseline start point as the pad and rotor wear. This is nice but it has a few problems when the wheel, and thus the rotor, are removed from the bike. If the brake lever is activated while the wheel is out and there is not a shim between the pads, the pistons can move too close together and the gap between them becomes too narrow and they'll rub the rotor. In extreme cases, the pistons can come clear out of the caliper body.

The fix is fairly easy, but care is required to not damage the pistons or the rubber diaphragm that creates the return force that brings the pistons back to their ready position. This is easiest to do with the wheel off and pads out of the caliper. I'll sumerize a bit of the information here, but Park Tool's, Shimano Hydraulic Disc Brake Service is the go-to reference for this and other situations related to disc brakes.

First, with wheel off and pads out, take a thin flat tool such as a standard screwdriver or a tire lever and carefully use it to push the pistons back into the caliper body. A steady force directed evenly on the piston face for a few seconds should cause the piston to retract into the caliper body. I usually do one side at a time, but the broad enough tool can be placed between both pistons and twisted so that both edges of the tool come into contact with each piston and as the twisting force continues the tool will push the pistons into the caliper as it tries to make room to rotate. It's a similar motion to turning a key in a lock. Wooden tongue depressors work well as do the sticks from a DQ Dilly bar, essentially a fat popcicle stick. If the pistons refuse to return fully into the caliper body, or they tend to move back out after tool pressure is stopped, the system may be overfilled. At the lever, with the reseivoir level to ground (usually requires the lever to be rotated up from it's down angle position on the bars), open up the bleed port cap with it's o-ring. Best to just remove it as the threading is very short and the o-ring can still be sealing the system even when loose. Return to caliper and push the pistons back into caliper. Excess oil will be forced out the bleed port. Return the cap and it's o-ring to the port and tighten. You've now reset the pistons and can return pads and springs to the caliper. The spring has right and left sides, designated by an R and L engraved on each side of the spring's arch. I cannot determine a difference in the spring's sides and brake pads that have the little handle with the hole which comes up from the center of the pad have no right-left designation and can be used on either side, however I'm always careful to have the spring oriented correctly when returning the assembly to the caliper.

Returning the wheel to the bike, again, fully engaged and centered in the dropouts, spin the wheel. There should not be any rotor rub what so ever at this point. If there is, that's an indication of significant misalignment somewhere. Anything from incorrect wheel placement in the drop-outs, rim not centered with it's hub, improper rotor installation, warped rotor, etc. If the wheel spins freely, note the position if rotor between the pads. Does it run centered or very close to it? Note the degree and direction of any offset from center. Go ahead an pull the brake lever. The first pull or two will be a longer pull and may feel soft. Subsequent lever activation will firm up and not as much distance to the bite point will be noted. Release the lever, spin the wheel and check for pad rub on the rotor.

If the pads still rub on the rotor for most or all of the rotation, this indicates the need to center the caliper to the rotor (given nominal wheel and rotor installation). This, too, is easily performed by loosening the caliper's fixing bolts so that the caliper has free side to side play (if an adapter is being used, be sure not to loosen it's fixing bolts going to the bike or fork frame as opposed to the caliper fixing bolts that are received into the adapter). Next, with the caliper loose, I like to spin the wheel and then pull the brake lever fully and hold it closed. If you're alone you can wrap something around the lever and handlebar to secure the lever in the closed position. While the brake pads are engaged on the rotor, tighten up the caliper fixing bolts. I go back and forth between the bolts snugging one up then the other, back to the first for maybe a ¾ to a full turn, then the other, essentially torquing them up together. I've noticed that keeping the Allen key very straight and putting the torque on it in such a way as to minimize any lateral forces imbued to the bolt and thus the caliper mounting aspects, the results are more satisfactory. After the bolts are tight, release the lever, spin the wheel and see about rub. Over 75% of the time, if no other anomalies are present, this fixes pad rub.

Sometimes the above fails. If the rub is intermittent, you may have a rotor out of true in a spot and that will need to be corrected. This is discussed in the linked Park Tool tutorial, and based on your described symptoms appearing after having the wheel off, it's not the most likely culprit.

5
  • okay ill try it, don't have a wedge for the callipers as i bought second hand just over a month ago Mar 3 at 12:42
  • A folded playing card or similar works. Excessive moving of the bike or putting it in windy conditions like a vehicle carrier would require securing the playing card wedge a little better, but it essentially stays in place very well.
    – Jeff
    Mar 4 at 6:09
  • Am I the only one who never seems to have any luck with the “squeeze the lever to align the caliper” method? On every build or repair that I’ve tried it, I still had to go back and align the caliper by sight every time that I can recall.
    – Pisco
    Apr 2 at 13:00
  • @Pisco the "squeeze to align" sometimes needs a temporary thin shim around the rotor, between the pads. A piece of paper or a folded business card can be ideal.
    – Criggie
    Apr 2 at 23:44
  • @Pisco The squeeze to center is a bit of an imperfect technique but does work more often than not for me. You can fine tune the caliper centering method by loosening one bolt at a time and squeeze to center or move that end of the caliper by hand. Also when tightening the bolts, go back and forth between fixing bolts so they more or less get torqued down together.
    – Jeff
    Apr 5 at 13:02

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.