A careful brake bleed can restore a firm lever and consistent braking, but the correct kit, fluid and procedure must be used for your exact brake.

Hydraulic disc brakes rely on fluid to transfer pressure from the lever to the caliper. Air inside the system can make the lever feel soft, allow the bite point to move or reduce braking consistency. Bleeding removes trapped air and, depending on the procedure, replaces old fluid.

This guide covers the preparation and general process involved in bleeding bicycle brakes. The fittings, lever position and bleeding sequence vary between manufacturers, so always follow the service instructions for your exact brake model.

If you have not selected a kit yet, start with our Brake Bleed Kits: Which Kit Do You Need? buying guide. It explains the differences between Shimano, SRAM DOT, SRAM mineral-oil, Magura, Tektro, TRP and other systems.

Start With the Correct Brake Fluid

Before opening the brake system, confirm whether it uses mineral oil or DOT fluid. Never mix the two. They are chemically different, use different seals and require separate bleed equipment.

• Shimano brakes use Shimano-compatible mineral oil.
• Magura brakes use the manufacturer-specified mineral oil.
• Tektro and TRP hydraulic brakes generally use mineral oil.
• SRAM Maven, Motive and DB8 brakes use SRAM mineral oil.
• Many SRAM Code, Guide, G2, Level and older Avid brakes use DOT fluid.
• Hope, Hayes and Formula compatibility varies by model.

Do not choose the fluid from the brand name alone. Check the marking on the lever or caliper and consult the manufacturer’s instructions for the exact model.

You can find suitable products in our Brake & Suspension Fluid collection.

What You Will Need

• A bleed kit compatible with the exact brake
• The manufacturer-approved mineral oil or DOT fluid
• The correct bleed block
• Suitable hex and Torx tools
• A torque wrench where specified
• Clean lint-free cloths
• Isopropyl alcohol suitable for cleaning brake components
• Nitrile gloves and eye protection
• A suitable container for collecting used fluid

Shop our Brake Bleed Kits, or use our bleed-kit buying guide if you are unsure which fittings you need.

Protect the Bike and Work Area

Brake fluid can damage paint, finishes and other components. Support the bike securely and cover painted surfaces around the lever and caliper. Keep clean water available when working with DOT fluid and follow the handling instructions supplied with the fluid.

Use fresh fluid from a clean, sealed container. Do not return used fluid to the original bottle and do not reuse fluid collected during a bleed.

Keep mineral-oil and DOT-fluid equipment completely separate. A syringe or hose previously used with one fluid type should never be used with the other.

Remove the Wheel and Brake Pads

Remove the wheel and brake pads before performing a full bleed. Store them away from the work area where they cannot be exposed to fluid, dirty tools or oily hands.

Fit the correct bleed block between the caliper pistons. The block holds the pistons in the correct position and prevents them from extending while the wheel and pads are removed.

Do not pull the brake lever unless the rotor, a suitable pad spacer or the correct bleed block is fitted. Pulling the lever with nothing between the pistons can cause them to extend too far.

Leaving the pads installed may appear quicker, but even a small drop of fluid can contaminate the friction material. Removing them is a simple precaution that can prevent noise, poor braking and an unnecessary set of replacement pads.

Position the Brake Correctly

Adjust the bike and brake lever into the position specified by the manufacturer. Some brakes require the reservoir or bleed port to sit level, while others use a particular lever angle to help trapped air move towards the bleed port.

Check that the hose follows a smooth path without high points where air can remain trapped. You may need to rotate the handlebar or reposition the caliper during the procedure.

Prepare the Bleed Kit

Identify the correct adaptors for the lever and caliper before filling the syringes or funnel. Make sure every hose is securely attached and that the syringes move smoothly.

When filling a syringe, hold it upright and gently remove any trapped air before connecting it to the brake. Introducing air through the bleed kit makes the job more difficult.

Do not force a fitting into a bleed port. Brake fittings can look similar while using different threads or sealing systems. The wrong adaptor can damage the brake or fail to seal properly.

Bleeding the Brake

Brake manufacturers use several different methods. Depending on the system, fluid may be pushed from the caliper to the lever, moved between two syringes or introduced through a lever-mounted funnel.

1. Install the manufacturer-specified fittings at the lever and caliper.
2. Open the bleed ports in the correct sequence.
3. Move fluid through the system slowly, following the brake manufacturer’s procedure.
4. Gently tap the hose and caliper to encourage trapped air to rise.
5. Operate or position the lever only as directed in the service instructions.
6. Continue until no further air bubbles appear and the exiting fluid is clean.
7. Close the bleed ports in the specified sequence.
8. Tighten the bleed screws and fittings to the manufacturer’s torque specification.

Work slowly. Pulling a syringe too aggressively can draw air past a seal, while pushing too hard can disconnect a hose or force fluid out around a fitting.

Do not assume that one online procedure applies to every brake carrying the same brand name. Manufacturers may use different procedures across road, mountain-bike and different-generation brake systems.

Clean the Brake Before Refitting the Pads

Once the bleed ports are closed, remove the equipment carefully and wipe away any visible fluid. Clean the lever, caliper and surrounding areas using the method approved for the brake fluid and component finish.

Inspect the caliper before removing the bleed block. It should be clean and dry before the pads are reinstalled.

Check each pad for wear, glazing or contamination. Replace pads that are below the manufacturer’s minimum thickness, cracked, unevenly worn or contaminated with brake fluid, oil or grease.

Can Brake Pads Be Sanded?

Lightly sanding a glazed pad can sometimes expose a clean, even friction surface. Place clean, fine sandpaper on a genuinely flat surface and move the pad across it while keeping the friction face level. Remove only enough material to refresh the surface.

Sanding does not reliably recover a pad that has absorbed brake fluid, chain lubricant or another oily contaminant. Contaminated pads should be replaced, particularly if braking power has dropped or the noise returns after cleaning.

Sanding and bedding-in perform different jobs. Sanding refreshes a glazed pad surface. Bedding-in transfers an even layer of pad material onto the rotor so the two surfaces work together correctly.

Check the Brake Rotors for Wear

Brake rotors wear as well as brake pads. A micrometer is the preferred tool for measuring the braking track because it can reach past any unworn ridge around the outside edge. Measure the rotor in several places and compare the lowest reading with the minimum thickness marked on the rotor or stated by its manufacturer.

Compare the lowest measurement with the minimum thickness marked on the rotor or stated by its manufacturer. Do not assume that every rotor has the same wear limit.

• Many Shimano rotors must be replaced at 1.5 mm or less.
• SRAM 1.85 mm rotors must generally be replaced at 1.55 mm.
• SRAM 2.0 mm rotors must generally be replaced at 1.7 mm.
• Other brands and rotor models may specify different minimum thicknesses.

The figure printed or etched onto the rotor and the manufacturer’s current service information should take priority. Replace the rotor if it is at or below its specified minimum thickness.

A rotor should also be replaced if it is cracked, badly scored, significantly warped, heat damaged or showing an aluminium layer that should not be exposed.

Do Contaminated Pads Mean the Rotor Must Be Replaced?

Not necessarily. Brake pads are porous and can absorb brake fluid, chain lubricant and other contaminants. Once this happens, replacement is the safest option because sanding may remove only the surface contamination.

A steel rotor does not normally absorb fluid in the same way. Remove it from the contamination source and clean both sides of the braking track thoroughly with fresh isopropyl alcohol and a clean lint-free cloth. Use a fresh section of cloth until no residue remains.

Fit new pads, then complete the manufacturer’s bedding-in procedure. If the brake remains noisy, braking power is poor or contamination reappears, check the caliper and hose for leaks.

Replace the rotor rather than continuing to clean it when:

• It is at or below the manufacturer’s minimum thickness.
• It is cracked, badly scored, warped or heat damaged.
• It remains noisy or produces poor braking after thorough cleaning and bedding-in.
• The manufacturer requires a new rotor when changing pad compounds.
• The braking surface, aluminium core or carrier is damaged.

Refit and Centre the Brake

Remove the bleed block and reinstall the brake pads, pad spring and retaining hardware. Refit the wheel and confirm that the axle is correctly seated and tightened.

Pull the brake lever several times to move the pads back towards the rotor. The lever should become firm and its bite point should remain consistent.

Spin the wheel and check for rotor rub. If necessary, centre the caliper using the adjustment method recommended by the brake or frame manufacturer. Check that all caliper, rotor and axle hardware is secure.

Bed the Pads Into the Rotor

New or freshly resurfaced pads must be bedded in. In a safe, traffic-free area, accelerate to a moderate speed and apply the brake firmly to reduce your speed to walking pace. Do not lock the wheel and avoid coming to a complete stop while holding the brake on.

Repeat the process until braking power builds and the brake feels consistent. Allow the brake to cool if the rotor becomes excessively hot.

A proper bedding-in process creates an even transfer layer on the rotor. Skipping this step can leave a new pad feeling weak, inconsistent or noisy.

How to Stop Noisy Disc Brakes

Brake noise is not always caused by air in the hydraulic system, and bleeding a brake will not normally cure squealing by itself. Noise can come from contamination, glazed pads, poor caliper alignment, uneven pad deposits, loose hardware or a damaged rotor.

• Check that the pads are above the manufacturer’s minimum thickness.
• Inspect the pads and rotor for oil or brake-fluid contamination.
• Clean the rotor with fresh isopropyl alcohol and a lint-free cloth.
• Check that the caliper is correctly centred over the rotor.
• Confirm that the rotor, caliper and wheel axle are secure.
• Measure the rotor and compare it with the stated wear limit.
• Inspect the rotor for bends, heavy scoring, discolouration or heat damage.
• Lightly resurface glazed pads on clean, flat sandpaper, then bed them in again.

Some noise in wet or muddy conditions can be normal and may disappear once the brakes are dry. Persistent noise accompanied by weak braking usually points to contamination, glazing, uneven pad material on the rotor or an incorrect setup.

If the noise returns quickly, the pads smell oily or braking performance remains poor, replace the pads and thoroughly clean the rotor. Replace the rotor if it cannot be restored to consistent performance or is outside its wear specification.

Final Safety Check

Before riding, confirm that:

• The lever feels firm and does not pull back to the handlebar.
• The bite point remains consistent when the lever is operated repeatedly.
• There is no fluid leaking from the lever, hose, caliper or bleed ports.
• The pads, retaining hardware and wheel are correctly installed.
• The rotor is above its minimum thickness and is free from damage.
• The rotor turns freely without excessive rubbing.
• The brake produces adequate power during a controlled low-speed test.

Start with a slow test in a safe area before returning to normal riding. Do not ride the bike if the lever remains soft, a leak is visible or the brake does not produce dependable stopping power.

When to Bring the Bike Into the Workshop

A bleed may not solve a leaking hose, damaged piston seal, worn master-cylinder assembly, seized caliper piston or badly contaminated brake. If the lever will not become firm, the bite point changes repeatedly or fluid appears around any seal, the brake needs further inspection.

Brake work is safety-critical. If you are unsure about the fluid, fittings, rotor condition or bleeding procedure, stop before opening the system. Our Christchurch workshop can identify the brake, complete the bleed and check the pads, rotors and caliper setup at the same time.

Need the Right Bleed Kit?

Read our Brake Bleed Kits: Which Kit Do You Need? buying guide before ordering. It will help you match the kit and fluid to your brake rather than relying on the brand name alone.

You can also browse our Brake Bleed Kits and Brake & Suspension Fluid, or contact the Chain Reaction team if you need help identifying your brake.