Caliper Alignment — The Basics
Hydraulic disc brake calipers must be centered over the rotor — equal clearance on both sides. Most rub comes from a caliper that's shifted or a rotor that's slightly bent. Fix the caliper first, then assess the rotor.
Fixing Brake Rub
Use a 5mm Allen key to loosen the two caliper mounting bolts just until the caliper can move freely — about a half turn. Don't remove them.
Hold the brake lever firmly squeezed (this centers the pads against the rotor) and while holding the lever, tighten both caliper bolts snugly. Release the lever. Spin the wheel — it should now spin freely. This method works about 80% of the time.
Hold a light behind the caliper while spinning the wheel slowly. You should see equal light on both sides of the rotor through the caliper slot. If one side is tighter, loosen the bolt on that side slightly and nudge the caliper over. A piece of paper between rotor and pad can help you feel the clearance while tightening.
If rub persists after alignment, the rotor itself may be bent. Hold a finger lightly against the frame near the rotor and spin slowly — you'll feel any wobble. A slightly bent rotor can be straightened by inserting a rotor truing fork (or a wide flat tool) and gently bending it back. Very bent rotors should be replaced.
When to Bleed
Bleed your brakes when: the lever feels spongy or pulls further than usual, lever feel has changed after a crash, or it's been more than 12 months. Air bubbles in the hydraulic line cause sponginess. Bleeding flushes air out and refreshes the fluid.
Shimano Bleed (Mineral Oil)
Shimano brakes use mineral oil only — never DOT fluid. You need the Shimano bleed kit (syringe, funnel, and hose), Shimano mineral oil, and the correct bleed port screws. Work in a well-ventilated area and keep oil off the rotor and pads.
Rotate the lever so the bleed port faces upward. Remove the port screw and attach the bleed funnel. Fill the funnel with mineral oil. Attach the bleed syringe to the caliper bleed nipple (underneath). Push fluid slowly from the caliper up through the system until clear, bubble-free oil flows out the funnel. Remove the syringe, close the nipple, remove the funnel, and reinstall the port screw.
SRAM Bleed (DOT 5.1)
SRAM hydraulic brakes use DOT 5.1 brake fluid. DOT fluid is corrosive — protect your frame finish and don't mix mineral oil into DOT systems. Wear gloves. The bleed procedure is the same push-from-caliper method with SRAM's own bleed kit and hose/syringe setup.
On SRAM systems, the lever bleed port is usually covered by a rubber plug near the lever pivot. Some systems require a lever-open tool to hold the lever in an open position during bleeding to get full fluid flow through the system.
Bedding In New Pads
New or freshly bled brakes need to be bedded in to transfer a thin layer of pad material onto the rotor. Find a safe area and: accelerate to moderate speed, apply the brake firmly (but not to full stop) about 10 times. Braking power should increase noticeably after 5–8 passes. Don't drag the brake or stop completely during this process — you want heat cycling, not glazing.
After bedding in, allow 5 minutes of cooling before full-power emergency braking. The rotor and pads need to cool and stabilize the transferred material. Your brakes should now feel firm and consistent from the first application.