How to Bleed Your Brakes

Let’s start with a couple of basic precepts. Hydraulic fluid does not compress but it does pressurize. That is why hydraulic systems work. Your hand moves a lever that moves a piston. The piston moves fluid from the master cylinder down the line into the caliper. The caliper’s piston’s move outward and apply the brakes. You grip tighter and the caliper grips tighter. You let off the handle, the pressure releases and the spring in the master cylinder returns the piston drawing fluid back into the master cylinder. A check valve in the master cylinder keeps the fluid and pressure one-way during application.

Air is a problem in a hydraulic system. Air does compress. If air is in your hydraulic system a portion of the hydraulic effort that should be pressure making a component move is now compressing air and not giving you maximum efficiency. In fact, it may result in a crappy or dangerous situation. “Bleeding” is the activity that removes air out of the hydraulic system.

Brake fluid (also used in hydraulic clutch applications) has a tendency to degrade over time. Best practice is to change the brake fluid every year. Pick a day…Birthday…First Day of Spring…Easter…Memorial Day…doesn’t matter - just pick a day and change your fluid out every year on that day. It will only take one container. Cheap insurance in my opinion. “Flushing” is the activity that removes the old hydraulic fluid from the system replacing it with clean fluid. Flushing is only bleeding with a different goal and purpose.

Brake fluid is one of the most efficient paint strippers known to man. Remember Murphy’s Law, “If it can go wrong, it will go wrong at the worst possible time”. Murphy was an optimist. Go prepared.

What will you need? Depends on your machine to a bit. A large old towel to protect your machine. Screwdriver to remove the master cylinder cover. Appropriate wrenches to open and close the bleeder valves. Plastic tubing to control the flow of the waste fluid; and a container for the same. New container of the appropriate type of brake fluid for your machine from a reputable manufacturer.

Step 1: Protect your painted surfaces with toweling.

Step 2: Locate your bleeder valves (some machines have one for each half of each brake caliper, others only one per caliper/slave cylinder). Clean away any dirt or debris near the bleeder. Hopefully it has a cap to keep crap from stopping up your bleeder. Bleeder caps are your friends.

Step 3: Loosen and re-tighten your bleeder valves without any pressure in your system - just to make sure none of them are seized. Just crack it open and closed to make sure it moves.

Step 4: Place tubing on your bleeder to control waste fluid. You do not want it shooting out on any painted surfaces. It is good to have a container to route the fluid to. I use IV bags. EMS types are your friends.

Step 5: Wipe away any debris from around your master cylinder. Remove the screws and raise the cover. Inspect the diaphragm for dry rot or tears. Wipe all the small parts down with a clean lint free rag (t-shirts & diapers rock).

Step 6: Inspect & Evaluate. Brake fluid is supposed to be generally clear. A member here described his as, “looking like pancake syrup”. If you have a reason to bleed your brakes there is a good chance you should be flushing your fluid while you’re at it. Look in the bottom of the master cylinder for…what I call black dust. If you have black dust or brown fluid use a baster bulb to draw the fluid out. Use q-tips, pipe cleaners or an old piece of clean T-shirt on a screwdriver tip to get that black dust out as well as any residual fluid. Put nothing into your hydraulic system other than the appropriate type of clean (new) brake fluid.

Step 7: Once the master cylinder is clean top it off with new fluid.

Consult your owner manual or read the master cylinder’s cover for the correct grade of fluid. Lightly install the cover back in place.

Be sure that your check valve cover did not get dislodged or lost. They can pop loose while cleaning. They will pop right back in - they only fit one way

Start pressuring the system by pulling the lever back and forth rapidly about 10 - 25 repetitions. When you have a firm lever, hold it back against the bar.

Step 8: Starting with the caliper that is farthest from the master cylinder (left side front dual disc) open the bleeder valve. This might require an assistant. I usually assign my assistant to running the lever. When the bleed valve opens fluid and air will spit out (or just fluid - using clear tubing will help you see what’s going on) and the lever will release to the bar. DO NOT LET GO OF THE HAND LEVER WHILE THE BLEEDER VALVE IS OPEN. That will suck air into the system through the bleeder valve and cause more problems than you had when you started. Close the bleeder valve, then let go of the lever and continue the cycle of pumping, holding and releasing. Once the far side runs clear, change to the near side.

Step 8: Repeat this basic process for the clutch hydraulic system as well as the back brake system. One can usually do those without an assistant.

The black dust? That is usually a sign that the rubber components inside the hydraulic system are starting to break down. I know that my clutch system is almost ready to be rebuilt. The fluid gets nasty in about 3 months. I have the cylinder rebuild kit on hand but still need to get the stainless steel brake line upgrade.

Maintaining your brake system is low cost and easy. It will pay dividends when you have to replace pads and do not have to deal with stuck or leaking pistons and cylinders. An efficient brake system is essential to safe riding.