Slide pin stuck on? Sometimes the rubber around the end deteriorates:
Incorrect choice of lubricant can eat away the rubber, which then swells, sticks and tears – make sure to only use slide pin grease!
A normal slide pin rubber piece should look like this (dust boot removed, but identical slide pin):
The rubber piece does not appear to be available (or readily available, at least as far as we can find) as a separate part – we cannibalised another set of calipers for the above one in good nick.
If your slide pin rubber looks like the one in the top pic, there’s a good chance that it’s sticking inside the caliper and making it hard for your brake pads to move back away from the disc once you let off the brake lever – meaning that your brakes will stick on, with negative consequence for pad/rotor longevity, braking performance and consequently safety!
Don’t forget, there are plenty of other reasons why a front brake might be sticking – it’s worth investigating the lot if that’s your issue, as there may be more than one problem in the mix.