A good brake bleed should leave you with a firm lever, a consistent bite point and dependable braking. The job is not especially complicated, but you must use the right fluid, fittings and procedure for the brake in front of you.

Hydraulic brakes transfer pressure through fluid inside the hose. Once air gets into the system, the lever can feel soft, pull closer to the handlebar or develop a bite point that changes between pulls. Bleeding removes that trapped air and, depending on the procedure, replaces old fluid at the same time.

Shimano, SRAM, Magura, Tektro and TRP brakes are not all bled in the same way. This guide covers the preparation and general process, but you should still follow the service instructions for your exact model.

If you are still working out which kit you need, start with our Brake Bleed Kits: Which Kit Do You Need? guide.

Get the Fluid Right Before You Start

First, confirm whether your brake uses mineral oil or DOT fluid. Never mix them. They are chemically different and the seals inside the brake are designed for one or the other.

• Shimano brakes use Shimano-compatible mineral oil
• Magura brakes use the mineral oil specified by Magura
• Tektro and TRP hydraulic brakes generally use mineral oil
• SRAM Maven, Motive and DB8 use SRAM mineral oil
• Many SRAM Code, Guide, G2, Level and older Avid brakes use DOT fluid
• Hope, Hayes and Formula systems vary, so check the exact model

Do not choose fluid from the brand name alone. SRAM is the obvious example because it produces both DOT-fluid and mineral-oil brakes. Look for a fluid marking on the lever or caliper, then confirm it against the service information for that model.

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

What You Will Need

• A bleed kit made for your brake
• The correct mineral oil or DOT fluid
• The correct bleed block
• Suitable hex and Torx tools
• A torque wrench where required
• Fresh medium-strength threadlocker if removing a six-bolt rotor
• Clean lint-free cloths
• Isopropyl alcohol suitable for cleaning brake components
• Nitrile gloves and eye protection
• A container for the old fluid

You can browse our Brake Bleed Kits, or use the buying guide above if you are unsure which fittings you need.

Keep DOT and Mineral-Oil Tools Separate

A syringe or hose used with DOT fluid should not later be used with mineral oil, even if it looks clean. We keep the two systems separate in the workshop and recommend doing the same at home.

Use fresh fluid from a clean container. Do not pour used fluid back into the bottle or reuse fluid collected during a previous bleed.

DOT fluid can damage paint and some finishes, while mineral oil can leave slippery residue and contaminate braking surfaces. Cover the bike around the lever and caliper, then clean any spill immediately using the method recommended for that fluid.

Remove the Wheel and Brake Pads

For a proper bleed, remove the wheel and take the brake pads out. Store them somewhere clean, well away from open fluid, dirty tools and oily hands.

We regularly see brakes that started squealing after someone left the pads installed during a bleed. It only takes a small amount of fluid to ruin the friction material, so removing them is worth the extra couple of minutes.

Fit the correct bleed block between the caliper pistons. This holds them in the right position and prevents them from extending while the wheel is out.

Do not pull the lever with nothing between the pistons. If they extend too far, you can create another job before the bleed has even started.

Position the Brake and Prepare the Kit

Set the lever at the angle required by the brake’s service instructions. Some reservoirs need to sit level, while other systems use a different position to help air move towards the bleed port.

Check the hose path as well. A high point or tight loop can hold an air bubble, so you may need to turn the handlebar or reposition the bike during the bleed.

Work out which adaptor goes where before filling anything with fluid. Fittings can look almost identical while using different threads or seals. If one does not screw in easily, stop and check it rather than forcing it.

Make sure the hoses are secure and the syringes move smoothly. Hold a filled syringe upright and work out the trapped air before connecting it to the brake. Otherwise, you are adding fresh bubbles to the system you are trying to bleed.

Bleeding the Brake

The method depends on the brake. Shimano commonly uses a lever-mounted funnel, while many SRAM systems use two syringes. Other brakes may be bled from the caliper upwards or use their own sequence.

1. Fit the correct bleed block, adaptors and hoses.
2. Move the fluid slowly using the sequence specified for the brake.
3. Work trapped air out of the caliper, hose and lever as directed.
4. Close the bleed ports in the correct order and tighten them to the stated torque.
5. Clean the brake thoroughly before reinstalling the pads.

Do not rush this part. Pulling hard on a syringe can draw air past a seal, while pushing too aggressively can disconnect a hose and send fluid across the bike.

Once the lever feels firm, change the angle of the bike and check the lever again if the service procedure allows. A small bubble can sometimes hide in the hose or lever and only become noticeable when the bike is pointed uphill, downhill or stored vertically.

Clean the Brake and Check the Pads

Once the bleed ports are closed, remove the equipment carefully and clean the lever, caliper and surrounding area. The caliper should be completely clean and dry before the bleed block comes out and the pads go back in.

Inspect the pads while they are removed. Replace them if they are below the stated wear limit, cracked, unevenly worn or contaminated with oil or brake fluid.

Can You Sand Brake Pads?

Sometimes. If a pad is glazed but otherwise in good condition, lightly resurfacing it can expose a clean, flat 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 is not a reliable fix for a pad that has absorbed brake fluid, chain lubricant or another oily contaminant. Pads are porous and the contamination may sit deeper than the surface. If braking power has dropped or the squeal quickly returns, replace the pads.

Sanding and bedding-in are 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 properly.

Brake Rotors Wear Too

Rotors do not last forever. Measure the braking track with a micrometer in several places and use the lowest reading. A micrometer can reach past the unworn ridge that often forms around the outside edge of the rotor.

Always follow the minimum thickness marked on the rotor or listed by its manufacturer. Common examples include:

• Many Shimano rotors require replacement at 1.5 mm
• SRAM 1.85 mm rotors generally require replacement at 1.55 mm
• SRAM 2.0 mm rotors generally require replacement at 1.7 mm

These figures do not apply to every rotor. The marking on the rotor and the current specification for that model take priority.

Replace a rotor if it is at its wear limit, cracked, badly scored, significantly warped or heat damaged. A rotor with an exposed aluminium layer or damaged carrier also needs replacing.

Do Contaminated Pads Mean You Need a New Rotor?

Not automatically. Pads can absorb oil and brake fluid, but a steel rotor normally does not absorb contamination in the same way.

Remove the source of the contamination, then clean both sides of the rotor thoroughly with fresh isopropyl alcohol and a clean lint-free cloth. Keep changing to a clean part of the cloth until no residue appears.

Fit new pads and bed them in properly. If the brake is still noisy or lacks power, check the caliper, hose and fittings for a leak before blaming the new pads.

We would replace the rotor if it:

• Is at or below its minimum thickness
• Is cracked, badly scored, warped or heat damaged
• Has a damaged braking surface, aluminium core or carrier
• Still performs poorly after thorough cleaning and correct bedding-in

Refit and Centre the Brake

Remove the bleed block and reinstall the pads, pad spring and retaining hardware. Refit the wheel and make sure the axle is fully seated and tightened.

The rotor does not normally need to be removed for a brake bleed. If it has been removed for cleaning, inspection or replacement, take care when reinstalling it.

If you have removed a six-bolt rotor, we strongly recommend using fresh medium-strength threadlocker when reinstalling the rotor bolts, unless the bolts already have a fresh pre-applied locking compound or the manufacturer specifies otherwise.

Clean the bolt threads first, apply the threadlocker sparingly and tighten the bolts gradually in a crossing pattern to the rotor or hub manufacturer’s torque specification. Do not use high-strength permanent threadlocker, as this can make the bolts extremely difficult to remove later.

Centre Lock rotors do not use rotor bolts. Clean and refit the lockring, then tighten it to the torque specified by the hub or rotor manufacturer.

Pull the brake lever several times to move the pads back towards the rotor. The lever should become firm and return to the same bite point each time.

Spin the wheel and check for rotor rub. Centre the caliper if necessary, then check the axle, caliper bolts, rotor hardware and pad-retaining hardware before riding.

Bed the Pads In

New or freshly resurfaced pads need to be bedded into the rotor. Find a safe area away from traffic, build up moderate speed and brake firmly until you are down to walking pace. Avoid locking the wheel or coming to a complete stop with the brake held on.

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

Skipping the bedding-in process can leave a perfectly good set of pads feeling weak, inconsistent or noisy.

What About Noisy Disc Brakes?

A bleed removes air from the hydraulic system. It does not normally cure squealing by itself.

Noise is more commonly caused by contaminated or glazed pads, poor caliper alignment, uneven pad deposits, loose hardware or a damaged rotor.

If a brake is noisy, check:

• Pad wear and condition
• Pad and rotor contamination
• Caliper alignment
• Rotor thickness and condition
• Rotor, caliper and axle hardware
• Whether the pads have been bedded in correctly

Some noise in wet or muddy conditions is normal and often disappears once the brake dries. Persistent squealing combined with poor braking usually points to contamination, glazing or an uneven transfer layer.

If the pads smell oily, the noise quickly returns or braking remains weak, fit new pads and clean the rotor thoroughly. If the contamination comes back, look for a leak around the caliper, hose or fittings.

Final Check Before Riding

• The lever feels firm and does not pull back to the handlebar
• The bite point remains consistent
• No fluid is leaking from the lever, hose, caliper or bleed ports
• The pads, retaining hardware, wheel and axle are secure
• The rotor is above its wear limit and free from damage
• The wheel turns without excessive rotor rub
• The brake produces dependable power during a low-speed test

Begin with a slow test ride somewhere safe. Do not ride the bike if the lever remains soft, the bite point keeps moving, a leak is visible or the brake does not produce reliable stopping power.

When It Is More Than a Bleed

Not every soft or inconsistent lever is caused by air. A leaking hose, damaged caliper seal, sticking piston or worn master cylinder can prevent the brake from working properly no matter how carefully it is bled.

The master cylinder sits inside the brake lever and creates the hydraulic pressure that operates the caliper. As its piston and seals wear, the lever may return slowly, lose pressure or develop a bite point that changes from one pull to the next.

A lever that gradually sinks under steady pressure or still feels wrong after a careful bleed can also point to worn or damaged internals.

Rebuild parts are available for some brakes. Others require replacement of the complete lever or master-cylinder assembly. The right repair depends on the model, its age and whether service parts are still available.

We see bikes that have been bled several times when the real problem is worn lever internals, a leaking caliper, contaminated pads or a rotor below its wear limit. If the lever will not become firm, returns slowly, changes bite point or shows signs of leaking, inspect the complete system rather than bleeding it again.

Need the Right Kit or Some Workshop Help?

Read our Brake Bleed Kits: Which Kit Do You Need? guide before ordering. It will help you match the fittings 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.

If you would rather leave the job to us, bring the bike into Chain Reaction in Christchurch. We can identify the brake, complete the bleed and check the lever internals, pads, rotors and caliper setup at the same time.