How to bleed MTB brakes

According to a survey I posted in the YouTube community section last week, 32% of you

bleed

your

brakes

. 21% of you have a brake

bleed

ing shop and I can't blame you. There are no shortage of reasons to let someone else do it, especially if you live in an apartment. As for the remaining 46% of you, it's not about the knowledge, the tools, or the mess. You just don't know what a weird brake bleed is, plain and simple. This is good because today that is going to change. Even today's most basic mountain bikes have disc

brakes

. Some use cables, while others use oil-filled hoses.

Hydraulic brakes are powerful and precise, which is why cars and motorcycles have used them for almost a century. Hydraulic brakes on a bicycle consist of a lever, a hose and a caliper. This closed system is filled with oil, so when you pull the lever, the oil moves, forcing the caliper pistons to squeeze the rotor. But why are these systems full of oil? Why not a gas like air? Well, air is easily compressed, which is why it is ideal for suspension forks. Filling a fork with air guarantees that it will move when you hit a bump. But if we filled your fork's air chamber with oil or some other liquid, it would feel completely stiff.

As for cable-actuated brakes, they work fine, but there is friction between the cable and the housing, plus some bending and stretching. This results in a loss of energy that hydraulic systems can overcome. But hydraulic brakes are prone to wear and contamination. Air can pass through the seals and become part of the system. Air in the system makes the lever feel spongy and reduces brake effectiveness. A brake service may involve flushing the system and replacing old oil, but more often it just involves removing air bubbles. This process is called bleeding, but why? Why not a fart? At the end of the day, we are trying to get air out.

Good question. The term originated in automobile shops, where some procedures involved dripping some oil from the caliper, hence the term "bleeding." But on a bicycle the procedure can vary greatly depending on the brand and model. Each brake model requires a different set of tools, a different oil, and a unique set of steps. That's why most manufacturers include detailed tutorials on their YouTube channels. As detailed as they are, these tutorials assume a basic level of understanding that a bike mechanic or enthusiast would have. Otherwise, you don't know what monster they are talking about. Today that is going to change.

We'll build a transparent model so you can see how a bleed works. The system uses a lever and gauge made from syringes, connected together with clear aquarium tubing. I even cut this trigger out of wood, which turns out to look like a nose. At the end of each syringe there is a connector that includes a purge port that we can cover. This is far from a perfect representation of a hydraulic disc brake, as it is not very well sealed, only has one piston, and is filled with vegetable oil. But pull the nose and the caliper moves.

As you can see, there is quite a bit of air in this system. This requires bleeding. To bleed any brake system you need a bleed kit. Mine contains oil, two syringes and a purge block. We will install the bleed block first to prevent the piston from moving. This will ensure that we end up with the correct amount of fluid in the system. Next we will fill our syringe with brake oil, and we will take care of removing all the air by turning it over and letting the bubbles rise towards the opening. This is also an important step in an actual bleed, since you don't want to pump more air into the brake system.

To connect the syringe we will open the purge port at the bottom. Notice how it doesn't drip as much. The same thing happens if you fill a straw with water. If you open one end, the liquid practically stays there. But if you open both ends, it comes gushing out. The same goes for a hydraulic brake system. Open only one end at a time. Once we have our syringe attached, we can open the bleed port on the top and attach another syringe to collect the excess liquid. Now we will pump oil from below through the system. Excess oil flows into the syringe at the top, as does a good amount of air.

You can see how pulling up on the top syringe creates negative pressure and forces the bubbles out of the nooks and crannies. Pulling the lever also expels bubbles from the system. In theory, we could remove the lever or caliper from the bike and tilt it in different directions to allow trapped air to flow upward. Position is also important on real bikes for more reasons than one. When we are satisfied, we can close the system one end at a time and remove the purge block. Now our brakes are working. There isn't a big difference because this system wasn't very refined in the first place.

Like our model, real hydraulic brakes have bleed ports. They usually have nooks and crannies that can trap air. And pulling the lever is usually a step in actual brake bleeding procedures. To purge my Magura MT5, the process is very similar to our model. You pump liquid from bottom to top, move the lever and bubbles come out. There are quite a few other steps, but they are easy to understand. For example, it is necessary to remove the wheel and brake pads to prevent them from becoming contaminated with oil. And like our model, bleed blocks are installed to keep the pistons located.

Also, our model used vegetable oil, while my MT5s use a Magura mineral oil blend. In Shimano brakes, oil is poured into this funnel to displace the air. On some Hope brakes, the entire top of the lever is removed and filled. In each case, a specific type of oil and set of tools are required to complete the process. So if you want to try bleeding your own brakes, here are the steps. Step 1. Order a specific bleed kit for your brake model. There is a special online tool you can use to find this called Google. The bleed kit will come with everything you need, including the right oil for your brakes.

When you run out, you'll just have to order more oil, as the rest of the purge kit will be reusable. Step 2. Get some additional supplies. Rubber gloves would be first on the list, as brake oil is unpleasant and you want to have clean hands when reinstalling the pads. Rags and a spray bottle filled with water or alcohol are also helpful. For any bleed, you'll also need basic shop tools, but if you're bleeding your own brakes, I assume you've already stocked up on some Torx and hex wrenches. Proceed to step 3. Find a tutorial specific to your brakes.

Most manufacturers have them, but I would actually recommend the ones made by the shops and my friends at Global Mountain Bike Network. These tutorials may seem too detailed at first, but now that you know the basics I think they will make more sense. Watch your tutorial several times and make a cheat sheet of the steps if necessary. Finally, step 4. Try bleeding the brakes. You're going to spill some brake fluid on the floor and probably miss the bleeder screw. You could even ruin the entire process and have to start over. But once you learn how to bleed your brakes, you'll find that it's easy to do.

Even better, you now know your system from start to finish. If the oil is old and discolored, you can flush and refill using virtually the same steps as purging. Still, some of you might be thinking, "This looks a little messy." I'd rather pay a store to do this. That's perfectly fine and the good news is that it's not expensive. Even a complete wash and bleed of the front and rear brakes will cost less than $50, and a quick touch-up can cost much less than that. So the next time you feel that spongy feeling on the levers, you'll know what to do.

Bleed the brakes or have a shop do it for you. I hope you found this video useful or at least entertaining. If so, please like and share it with someone who finds it useful. If you want me to do more overview videos like this on other maintenance procedures, let me know in the comments. If you're ready to try bleeding your own brakes, I also left some resources in the description. Thanks for traveling with me today and we'll see you next time.