Tools:
- Allen Key Set
- Cable Cutter
- Flashlight and Paper
Adjusting The Brakes
Mechanical Disc Brake Alignment
This article will help you gain the knowledge you need to adjust mechanical disc brakes.
If you are not confident in your ability to successfully and safely perform all steps, we recommend having the work performed or checked by a local, certified, and reputable bike mechanic.
Preliminary Information
Mechanical brake systems use a cable to actuate a lever arm on the caliper that engages the pads. Hydraulic systems use fluid through a hose to engage the pads. Disc brakes have long been the preferred braking method for modern mountain bikes. The braking force is applied to a disc that is bolted directly to the hub. They provide more stopping power, and better performance in bad weather than traditional rim brakes
- Brake Lever: The brake is actuated by a brake lever at the handlebars.
- Cable & Housing: On a mechanical system, the brake lever pulls a cable, which runs through the housing down to the brake caliper.
- Barrel Adjuster: The housing can effectively be lengthened or shortened with the twist of a barrel adjuster, which may be found at the lever and/or the caliper.
- Lever Arm: The brake cable actuates a lever arm. Most mechanical caliper designs have 1 lever arm that moves only the outer brake pad when actuated. The rotor then flexes over into contact with the innermost pad. There are also designs that have 2 lever arms. On these calipers, both pads move evenly into the rotor.
- Pinch Bolt: The cable is secured to the lever arm using the pinch bolt.
- Pads: The lever arm squeezes the brake pads to the rotor, causing friction to slow or stop the bike.
- Adjusters: Calipers are equipped with pad adjusters that move the brake pads in or out from the rotor. Some calipers have only one adjuster that moves the inner pad, while other calipers have both an inner and outer pad adjuster.
- Mounting Bolts: Caliper disc brakes secure to the frame or fork using two mounting bolts. The location of these bolts can vary depending on the frame mount standard.
- Mounting Holes: Disc brake systems are equipped with wide holes that allow for lateral movement relative to the rotor. These can be found on the caliper body (post mount), the frame (rear flat mount), or the caliper adapter (front flat mount).
Alignment Procedure
- Ensure that the wheel is fully seated in the dropouts. This, in turn, ensures that the rotor is properly positioned in the caliper.
- Elevate the bike, spin the wheel and inspect the rotor in the caliper. If the rotor shows a lot of lateral movement, it can be difficult or impossible to adjust the pads to not rub. The rotor will need to be trued or replaced.
- Turn the barrel adjusters all the way in (clockwise) at the lever and at the caliper if applicable.
- Check that the lever arm is released and in its relaxed position by loosening the cable pinch bolt. This ensures full lever arm travel during braking.
- Pull the cable tight so it is free of slack and tighten the cable pinch bolt.
Be careful not to move the lever arm when tightening the pinch bolt. This is important because the lever arm only has a small amount of useful motion.
Final Adjustments
The end goal is a caliper that is parallel to the rotor, with even gaps on each side and an adequate lever feel. Even though setting the pads against the rotor should theoretically have aligned the caliper correctly, it is common for further adjustments to be required.
Lever Adjustment
- Pull and release the brake lever a few times to check the clearance at the grip. Check that the lever travel feels adequate to slow and stop the bike. Typically, the pads should feel like they are contacting the rotor at a minimum of one-half the lever travel.
- Make adjustments as necessary using the pad adjusters, moving the pads in and out evenly on both sides.
Pad Rub
- Spin the wheel and check for pad rub. If there is no pad rub, the alignment is complete. If the wheel slows quickly or makes a rubbing noise, the pads need further adjustment.
- Inspect the alignment of the pads to the rotor. You may need to reorient the bike for a better view. It is helpful to backlight the caliper body by shining a light on a piece of white paper or material. This makes the pad clearances easier to see.