What is brake bleeding?

Brake bleeding is the common procedure of removing air from the hydraulic brake line.

How do hydraulic brakes work?

Pulling your brake lever exerts pressure on the hydraulic fluid. Since fluid doesn’t compress easily, the pressure travels through the brake line to the caliper, which houses the pistons and brake pads to clamp onto the rotor and slow the wheels by friction. 

Why do my brakes need to be bled?

If you have to pull your lever all the way or nearly to the handle before your brakes kick in, you have what is commonly referred to as spongy brakes due to air in the brake fluid. Air compresses more easily as a gas, and when it enters the hydraulic line, it interferes with the brake responsiveness. Instead of the fluid transferring pressure from the lever to the caliper, you end up compressing the air in your brake line. 

How does air enter the brake system?

Air can enter the brake system when your brake pads get worn down. Thin pads cause the fluid level to drop, which lets air in. Every time you open the brake system, such as shortening a hydraulic hose or installing a new caliper or lever, air can enter the system. In addition, a damaged caliper or hose can lead to leakage of fluid and influx of air into the system. 

Do you need to completely flush your brake system?

Fluid gets dirty and breaks down over time, which is why you might need to flush the whole system to keep your brakes fully functional. The reason why you wouldn’t want contaminated oil is because dirt changes the viscosity of the fluid and hurts the fluid’s ability to dissipate heat, possibly even damaging the brake itself.

How often should I bleed my brakes?

When your brakes experience a reduction in functionality, it may be time to bleed your brakes. Some people service their brakes every year or two to keep them in top condition.

How difficult is it to bleed brakes?

Brake bleeding is a straightforward procedure. Once you've bled your first set of brakes you’ll wonder why you ever needed your local bike shop.

What do I need to bleed my brakes?

Generally, you’ll need the proper brake fluid specific to your brake model, a bleed kit, gloves, and basic hex and torx wrenches. 

How much brake fluid do I need to bleed my brakes?

From our experience, to bleed the entire front brake line, you need 10ml of mineral oil, and to bleed the entire rear brake line, you need 15ml of mineral oil. In other words, 60ml of mineral oil should be enough to bleed your front and rear brakes for two bikes. If this is your first time and you’re concerned about spills or not having enough fluid, we do sell a few kits that include 120ml of mineral oil, but if all goes well, you should be good with 60ml to bleed two bikes!

What is a bleed block?

The bleed block fits between the pistons of your brake caliper to prevent them from moving outwards during the bleed process. If you don’t have a bleed block, it’s around 10mm in thickness, so you can use a 10mm Allen wrench as a substitute.

Is your kit compatible with my brakes?

Check our compatibility list for the specific models that our kits work with! Note: our Shimano road and gravel kits are compatible with Shimano mountain bike brakes as well. The key difference is that if you buy our road and gravel kit, you'll be receiving an additional funnel adapter.