ASK MBA: WHY DO MY BIKE’S DISC BRAKE PADS KEEP RUBBING?

Mountain bike disc brake pad rub is annoying but there's a fix!

Rubbing brake rotors are not only annoying to listen to, but they can wear out parts prematurely.

 

WHAT’S THE RUB?

Q: My front brake pads keep rubbing no matter what I do. I center the pads and make sure everything is tight, yet by the end of every ride I can hear the pads rubbing on the rotor again. What is going on, and what am I doing wrong?
Cody Smith
Idaho

A: Brake pads rubbing on the rotor can be one of the most irritating things we come across as a rider, besides not being able to ride in the first place. Brake pads rubbing on the rotors are not only annoying to listen to, but they can hurt your efficiency and cause equipment to wear out prematurely. If you’ve centered your pads and checked that the axle and all the bolts are torqued to spec and still find the pads rubbing on the rotor, then you should make sure your rotor is straight.

 

It is possible to straighten lightly bent rotors but severely warped ones often need to be replaced.

 

If your rotor is okay, it’s most likely the caliper pistons sticking. Depending on your brake manufacturer, there are a couple of recommendations to try and fix the piston problem, so always check their recommendations first. Many brake manufacturers have detailed instructions on servicing and overhauling their brakes and these instructions should be followed. If any of these documents are confusing, stop and take your bike to a shop for proper service.

If this is happening with Shimano brakes, Shimano recommends removing the brake pads to expose the pistons and lubricate them with mineral oil. This can be done with a cotton swab to make sure you don’t use too much oil, and avoid contamination of the brake pads. After applying a small amount of mineral oil, push the pistons back into the caliper and cycle it several times to lubricate them, then reinstall the pads.

 

SRAM specifically reccomends cycling or “massaging” the pistons when setting up its new Maven brakes. We find it benificial on all of SRAM’s brakes.

 

If you have SRAM brakes, they specifically state to not apply DOT fluid, mineral oil or grease to the pistons when troubleshooting, as this can cause them to stick and make the problem worse. They do however sometimes reccomend lubing the pistons on initial assembly when seals or pistons are being replaced so be sure to follow their detailed instructions for your specific brake.

When troublshooting a sticky piston, SRAM recommends removing the brake pads and exposing the pistons, then pushing them back in four to six times in order to mobilize them. Some call this “massaging the pistons” and in our experience it does help SRAM brakes perform better. This will usually free up any binding that the pistons have and therefore should prevent the pads from continuously rubbing on the brake rotors. If you’ve done this and are still having the same problem, then it is likely time to take it to a good shop and have them take a look and check for a deeper problem.

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