We all know that disc brakes are the best braking mechanism that there is. These brakes are powerful and progressive.

The caliper is controlled by the cable, which forces the bike to stop immediately even at higher speeds. Most mountain bikes are fitted with an advance hydraulic system.

The calipers are placed on both sides of the rotor or the disc. When the brakes are squeezed, the calipers pressurize the rotation of the shaft from both sides, creating friction.

This friction is capable of reducing the speed of the rotational shaft and is ultimately able to stop the moving bike.

A lot of us are interested in having the most reliable brakes on our mountain bikes. We end up seeking answers to questions like, “How to fill disc brakes on a mountain bike?” Let us now go through a step-by-step process on how we can achieve that.

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Why should we get ourselves disc brakes anyway? 

Disc brakes have quite a few important benefactors which explain why they are becoming so popular in the world of cycling. Before we can move on to answer your query, “How to fill disc brakes on a mountain bike?” you should understand the answer to “why.”

Disc brakes will provide you with real control over your bike, which is much better placed than other braking mechanisms. The disc brakes are way more powerful, and it does not compromise on your overall control over the mountain bike.

One of the best reasons why you should get disc brakes is that no matter what the weather condition is, these brakes will never fail to deliver. It does not matter on what type of ground you are because disc brakes are perfect even for muddy off roads.

Step By Step Guide

First up, you need an array of tools to fill in disc brakes in your mountain bike. Before you get your hands dirty let us see what these tools are –

1st Step 

Make sure to have the bike stand up upright on a work stand. Then gently remove the wheels to access the bike better. The pistons of your brake pads need to be pushed into their bores. For this to happen, push in the flat-bladed screwdriver in between the brake pads. Pull out the brake pads and remove the pad retaining pin. You will now have to insert the bleed blocker in that gap between the two pistons of your brake caliper. The job of the blocker is to prevent the two pistons from shutting down the bleeding process.

2nd Step

Hex keys, also known as Wrench or Allen keys, are required to be used in the next step. The Allen key is the perfect tool used for tightening or loosening hexagonal fasteners or bolts. The brake lever bar clamp needs to be loosened by using the 4mm Allen key. This lever is required to be horizontal to the ground. Make sure to rotate the lever in that way. Then tighten it.

The bleed port screw needs to be removed by using the 2.5mm Allen key. You will find the bleed port screw on top of the lever’s reservoir. You should now remove the o-ring with the help of a pick. The cap may or may not come out with it. Now put in the bleeding cup into the opening of the bleed port, but make sure that you do not overtighten.

3rd Step

Calipers usually have a bleed nipple. Now gently take off the dust cover. Now, this is where you will have to use the syringe to pull out all the air bubbles. Once you get your bleed hose connected to the bleed syringe, you are required to fill in the mineral oil. You need to keep squeezing the syringe and observe the rising of air bubbles. Make sure that there is no more air left inside. The translucent hose will show you if there is any more air left or not, so keep an eye on it.

4th Step 

Once the oil is injected correctly into the system, you need to close the valve or the nipple and make sure no air enters the system now. After removing the hose and the fitting from the valve, tighten the rubber washer and the bleeder screw, one after the other.

 5th Step 

Make sure to remove the brake oil fluid because if it gets inside the disc brakes, it will permanently damage the performance of the brake pads.
To be able to do that, while removing the hose, steer it into a plastic bag and make sure fluid is coming out and depositing in that bag fitted at the mouth of the hose.

Do not forget to pump the brake lever a few times so that the fluid comes out completely. The disk brakes need to be cleaned by isopropyl alcohol if there is some kind of contamination caused by the brake oil fluid.

6th Step

Do not forget to remove the brake caliper from the bleed valve adapter. Replace the bleed nipple and gently put back the rubber dust cap the bleed nipple. The caliper and lever need to be mounted back on to the bike. Place the brake pads into their original place by continuously pumping the brake levers.

7th Step

Put the brake calipers in the middle of the disc. Always check for any leakages before you hit the road. If there are leaks, you will have to tighten the requisite bolts.

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Frequently Asked Questions

What is the functionality of a disk brake pad?

Brake pads take the heat every time you hate the brakes. This is why brake pads are more likely to face wear and tear than any other component of your bike. It is difficult to ascertain when the disc pads are running thin. However, frequent checking can keep you apprised of the situation. Moreover, if the disc brake pads become any thinner than 0.5mm, your bike will run the risks of frictions.

What is the ideal time to replace disc brake rotors?

Every time you hit the brakes, there is an erosion of your disc brake rotors. However, the disc brake rotors tend to last longer than disc brake pads. For every three brake pads, you should also consider changing the rotors. Do not forget to sync the replacement of your brake pads and brake rotors to achieve the highest level of efficiency.

What is a disc brake fluid?

The connection point between the lever and the caliper is filled with disc brake oil. The reason why you need to exert minimal pressure to stop the bike without having any difficulty is because of the fluid system.

The fluid gets dirty over time due to the deposition of debris and brake dust. There is a strong possibility of leaks and brake failures if the brake oil is too messy. This is why bleeding your disc brakes and changing the oil is necessary to keep your bike’s braking mechanism perfect. Frequent changing of brake oil will provide longevity to the bike components as well as security to your braking.


One of the major steps to end the answer to your query of “How to fill disc brakes on a mountain bike?” is to make sure that you clean and lubricate the piston in the caliper. This step will make sure that the disc brakes are fully functioning, effective, and secure for mountain bike riding.
Once you complete the entire process of bleeding your bike’s disc brakes, you will notice that the pistons and the pristine are moving in tandem. This process is extremely important for effective halting.

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