We are going to cover something that seems pretty basic but is absolutely necessary. And if not done correctly, can cause some serious damage: bleeding brakes and hydraulic clutches.

Since liquid can’t be compressed, if you confine it to a space and try to compress it, force is applied to everything in that confining space. As it relates to a brake system, we have a master cylinder that is holding the fluid. And inside that master cylinder is a piston that applies force to the fluid. That pressure is run down the brake line, where at the end of said brake line is a set of pistons in your brake caliper. The force pushes the brake pads against the brake rotor which then causes the bike to stop. So really it’s not that complex of a system. If you have ABS you will have an hydraulic control unit (HCU) and an electronic control unit (ECU) in line, which is what actuates the antilock brakes. The key to these systems all working correctly is that there can’t be any air in the system, which is where brake bleeding comes into play.

You’ll notice a little valve on the brake calipers. These are the bleeder valves. These need to be opened to allow fl uid and air to escape. The trick here is only having the valve open while fluid is exiting. It will need to be closed at any point there isn’t vacuum or pressure on the system so that you don’t draw any air back in. It really is that simple.

There are multiple ways to go about doing this, but we’ll start with the most efficient method, which is to use a pneumatic vacuum bleeder. This device will draw all the fluid from the master cylinder through the system very quickly. If you have ABS, a pneumatic pump is by far the most efficient method.

The second best way is to use a hand-operated vacuum pump. This will get you the same result as the pneumatic pump but at a much slower rate.

Option 3 is to reverse bleed it with a syringe. Basically open the valve and push fl uid through, close the valve and repeat the process. This. is time consuming but will get the job done.

Your last option is good old gravity. Open the valve and let the fluid slowly work its way through the system, bring a lunch and stay for the day if you’re going to try this because it takes forever. This process will not work if you have ABS, it will only work on non-ABS bikes where there is nothing in line between the master cylinder and the caliper.

If you are going to bleed your hydraulic clutch, it is the exact same process as the brakes, only difference is the bleeder valve is on the clutch slave cylinder.

There are a couple things I want to cover as it relates to brake fluid. As a Harley-Davidson owner you will either be dealing with DOT 5 or DOT 4 fluids. DOT 5 is used in earlier models and is non-corrosive. It needs to be clean fluid from a clean container that has not been exposed to water.

DOT 4 went into use when H-D introduced antilock brakes. This fluid is highly corrosive and will eat paint and powdercoat rather quickly, so if you have a spill it needs to be cleaned up immediately. It is in your best interest to cover any painted or powdercoated parts so that if you do have a spill you won’t have your finishes at risk. If you are doing this yourself use good quality brake fluid. At the shop we used the appropriate Motul product.

As with all the fluids on your motorcycle brake fluid has a serviceable life, and should be fully flushed every couple years. The. only other time you would need to bleed the brakes would be if you introduced air into the system either by replacing a part or having a failure at a fitting somewhere in line.

I would suggest if you are going to be working on your own bike that you invest in the appropriate service manual. It will be the best tool you have as you learn your specific motorcycle.

Until next time… Ride safe. HB

WORDS AND PHOTOS: DANNY WILSON