How to Bleed Hydraulic Brakes

Air in your hydraulic brake line means it needs to be bled, but could also be an indicator of other problems.

If your hydraulic brakes are spongy or don't grab well, they probably have air in the lines, and there are several things to check. It could be as simple as the brake fluid being added improperly the last time the system was worked on, or something as serious as air leaks caused by leaking fluid. Check for visible leaks on the master cylinder, caliper, brake line, and brake line fittings. Check the brake line for splits or kinks. On an old system it is usually a good idea to purchase a rebuild kit for the master cylinder and caliper with new gaskets, and to replace old brake lines and fittings. Look for leaks when you are bleeding your system whether you have just rebuilt them, or you are installing a new system. (The most common steps for bleeding hydraulic brakes by hand are shown below, but may or may not work on your specific application. Always follow the instructions that came with the brake system. If you are using a brake bleeding pump or other tool, follow the instructions that came with the tool.)
1. Open the master cylinder cap and fill to the indicated level on the master cylinder with the proper brake fluid that the manufacturer of the system recommends, usually a DOT 4 for Go Karts. Replace the cap.
2. Push the brake pedal slowly as you slowly open the bleed screw. Close the bleed screw before the pedal is fully depressed. Release the pedal and repeat as necessary. If your caliper has two bleed screws, repeat for each bleed screw because the caliper has two separate chambers which need to be bled separately. Always check the level of fluid in the master cylinder while you are bleeding the system. Do not let it run dry because this will allow air to enter the system, and you will have to start bleeding the system all over again. Keep filling the master cylinder as needed as you are bleeding the system. Depending on your system, you could fill the master cylinder a few times or many times, whatever it needs to do the job properly by eliminating all of the air in the system.
3. The system is bled properly when all that comes out of the bleed screw in the caliper is fluid and not air or bubbles. Tighten the bleed screw on the caliper (do not over-tighten), check for leaks, check for the proper fluid level in the master cylinder, replace the cap.
4. Ride the vehicle slowly at first to make sure the brakes are working.

Information on this page is intended as a guide only, and does not cover installation and function of every application of the subject discussed, but is only intended to supply information on the basic function.