How to Service Your Own Brakes (Rim and Disc)

Most brake service you can do at home is adjustment: take up cable slack, set pad position, center the caliper, and replace worn pads. Hydraulic bleeding, rotor problems and anything involving a bent or cracked part are different, and are better handled by a shop. Brakes are the part of the bike where a wrong guess costs the most, so this guide also says where to stop.

First, identify what you have. Rim brakes squeeze pads (also called shoes) against the wheel rim. Disc brakes squeeze pads against a metal rotor bolted to the hub. Disc brakes are either cable-actuated (mechanical) or hydraulic, where a sealed fluid line moves the pistons.

Before you start: check, then decide

Squeeze each lever with the bike stationary and push forward. The bike should stop rolling, and the lever should stop well before it touches the handlebar.
Look at the pads, the rim or rotor, and the cable or hose for wear, fraying, leaks or cracks.
Use the quick routine in the pre-ride checklist before every ride, and repeat the stationary test after any adjustment.
Look up the manufacturer’s instructions and torque values for your brake model. Torque figures for pad, caliper and rotor bolts vary by brand and model, so use the numbers printed on the part or in its manual rather than a general figure.

Rim brakes

Cable tension

If the lever travels too far before the pads touch the rim, the cable has stretched or the pads have worn. Turn the barrel adjuster (the threaded cylinder where the cable enters the lever or brake body) counterclockwise to add tension. If the barrel is nearly fully unscrewed, screw it back in, loosen the cable clamp bolt at the brake, pull the cable through a little, and retighten. Shimano’s setup method, as described by Sheldon Brown’s site, starts with the barrel set partly open: “Set the adjusting barrel 2-3 mm from fully closed.” That leaves room to adjust in both directions later.

Pad alignment and toe-in

The pad should land flat on the braking surface of the rim, clear of the tire and clear of the spokes. Toe-in means the front of the pad touches the rim first: “The shoe should be set so that the front edge of the shoe contacts the rim slightly before the rear edge.” Without toe-in, braking is weaker and the brake may squeal until the pad wears in.

Centering

Most calipers have a small screw that balances the spring tension on each side. Adjust it until both pads reach the rim together and the wheel spins without a pad dragging. If the wheel itself wobbles side to side, true it first; see how to true a wheel.

When to replace pads and what to check on the rim

Replace pads when they are visibly thin. Two points are worth knowing: as pad material wears on some cantilever brakes, “the shoe hits lower and lower on the rim, increasing the risk of ‘diving’ into the spokes,” so periodic checks matter. And a pad worn down to its metal backing will cut into the rim: “Replace the brake shoe before it wears a groove in the rim sidewall.” A rim worn that way is a structural concern, so have a shop assess the wheel before riding.

Squeal and weak braking from contamination

Persistent squeal is “usually caused by a new brake shoe that has not worn in, or by grease or oil on the rim.” Clean the rim: “Clean the rims with a good, oil-free solvent (citrus, alcohol, something like that.)” Keep lubricant off the rim and pads when you oil the chain or wash the bike; the washing guide covers what to avoid spraying near brakes.

Cable disc brakes

A cable disc brake has a screw or dial that moves the pad toward the rotor as pads wear. Alignment between caliper and rotor matters most: “Rotor-caliper alignment is critical so the rotor turns freely except when braking.” Check that the rotor is straight first, since “even a slightly warped rotor will keep the pads from being adjusted close enough without rubbing.”

The sequence described by Sheldon Brown’s disc-brake article is: take up cable slack so the arm rests against its stop, use the pad-spacing screw to bring each pad close, then loosen the caliper mounting bolts, which sit in slotted holes, and reposition the caliper so the two pads sit the same distance from the rotor. A thin spacer such as an index card between each pad and the rotor helps you judge the gap. Tighten the mounting bolts to the manufacturer’s torque.

Hydraulic disc brakes

“Hydraulic disc brakes are self-adjusting,” so pad wear does not need cable adjustment. What does need attention is air in the fluid, which makes the lever feel spongy and travel to the bar, and the pads and rotor, which wear.

Fluid type matters

Hydraulic disc brakes use one of two fluids, and they are not interchangeable. Wikipedia’s bicycle brake article states: “Two types of brake fluid are used today: mineral oil and DOT fluid.” It adds: “O-rings and seals inside the brake are specifically designed to work with one or the other fluid.” Sheldon Brown’s disc-brake article warns: “Improper reassembly or use of the wrong type of brake fluid will result in brake failure.” Check the brake’s manual for the fluid it specifies before opening any reservoir. Never top up with whatever is on hand.

Bleeding: take it to a shop unless you have the right kit

Bleeding procedures differ by brand and model and need the matching bleed kit and fluid. If your lever feels spongy, a shop bleed is the safe route. Do not ride a brake that has leaked fluid at a hose, fitting or caliper, or one whose lever pulls to the handlebar. Have it repaired first.

Disc pads and rotors: wear limits

Disc pads wear faster than rim pads: “Pads wear quickly compared with the shoes of rim brakes.” Wear limits vary by pad: “Wear limits are different for different pads — check manufacturer’s specifications.” Look up the minimum pad thickness in the brake’s manual, and replace pads before the metal backing plate can reach the rotor.

Rotors thin as they wear. Sheldon Brown’s disc-brake article gives a general guide: “With most brands, if the rotor is less than 1.5 mm thick, or seriously concave, it should be replaced.” It also notes that some brands specify other limits, such as 1.7 mm for Moment Industries and 1.52 mm for Hayes. Check your rotor and its manual for a brand-specific minimum, which takes precedence over any general figure. A bent, cracked or heat-discolored rotor should be replaced, not straightened by eye on the road.

Be careful with heat: “The disc gets extremely hot. It can cause injury if touched, and melt nearby plastic or cloth items.” Let the brakes cool before you handle them.

Test before you ride

Spin each wheel. It should turn freely, with no steady rub from a pad or rotor.
Squeeze each lever hard while stationary. The lever should feel firm and stop short of the handlebar.
Check that quick-release levers or thru-axles are closed and that all brake bolts are tight to the manufacturer’s torque.
Ride slowly in a safe, traffic-free area and brake progressively several times. New pads need some use before they reach full stopping power, and manufacturers publish their own break-in instructions; follow them.

Stop and see a professional if

A lever pulls to the handlebar after adjustment, or feels spongy even after the pads are correct.
Fluid is leaking anywhere on a hydraulic system.
A rim has a worn groove, a crack, or a dent at the braking surface.
A rotor is bent, cracked, or below its stated minimum thickness.
Cables are frayed or rusted inside the housing. The cable and housing guide covers inspection and replacement.
You are unsure what fluid your brake uses, or what torque a bolt needs.

Sources

Last reviewed: October 2026.