Bleeding the Brake System

Owned by Joseph Shneyderman (Unlicensed)
Last updated: Aug 23, 2023
3 min read

Table of Contents

This is a full guide on how to bleed the brake system from start to finish! This process requires at least 2 people, but is ideally done with 3 or 4.

What does bleeding the system mean? (Bleeding Overview)

Bleeding is the process by which air is removed from the hydraulic fluid in the brake system. This ensures that the fluid in the lines is incompressible, and the maximum clamping force can be applied by the calipers.

What can I do? (Roles + Responsibilities)

Roles

Responsibilities

Roles

Responsibilities

Bleeder

(ideally has experience bleeding the system)

  • loosens and tightens bleeder screw

  • holds tube and cup

  • watches tube for any bubbles in brake fluid

  • tells driver when to press brake pedal and when to let go

Driver

  • sits in car to press and hold brake pedal according to bleeder’s instruction

Filler

  • checks level of brake fluid in master cylinder reservoirs and fills as needed

  • can be done by Bleeder or Driver if necessary

Wiggler (Optional)

  • shakes brake lines to ensure any air in the lines makes its way to calipers

What should I do before I bleed the brakes? (Preparation + Supplies)

Before Bleeding:

  1. Gather all of your supplies:

    • Unused DOT4 Brake Fluid

    • Small Clean Funnel

    • 1/4 in Combination Wrench

    • Clear Tubing with a Small Inner Diameter

    • Disposable Cup or Bottle

    • Duct Tape

  2. Open Reservoirs and Check Fluid Levels

    1. Reservoirs should be as full as possible without risking overflow.

    2. If fluid level is low, the Filler should use funnel to pour clean fluid into reservoir until level is sufficient.

    3. Recap reservoirs when done.

  3. Reservoirs should be closed unless actively being checked or filled, and MUST BE CLOSED whenever bleeder screws are going to be opened.

  4. Use duct tape to attach one end clear tube at least halfway into disposable cup or bottle to avoid any spills.

Where do I start? (Order to Bleed Calipers)

The calipers should be bled in order of farthest away from the master cylinder to closest. That means:

  1. Rear Right

  2. Rear Left

  3. Front Right

  4. Front Left

Top-Down View of Chassis

How do I bleed the system? (Bleeding Process)

  1. Bleeder will place the box-end of the wrench over the top bleeder screw on the caliper, making sure that there is enough space for the wrench to turn at least 1/4 turn counter-clockwise, and place the clear tubing over the screw to create a seal (as shown below).

  2. Driver will press on the brake pedal three times before holding the pedal down. Driver will tell Bleeder that they are holding the pedal down, and Bleeder will turn the wrench a 1/4 turn counterclockwise to open the bleeder screw. Fluid will flow into tube, and the pedal will become easier to press down on.

  3. Wiggler will shake brake lines anytime bleeder screw is open.

  4. Bleeder will turn the wrench clockwise to close the bleeder screw, and tell the Driver to release the pedal.

  5. Filler will open the resevoir of the master cylinder corresponding to the caliper being bled (front or rear). Filler will add more brake fluid to the reservoir if necessary, using the funnel, the close the reservoir.

  6. If there are BUBBLES present in the fluid coming out of the bleeder screw:

    1. Bleeder will check the edges of the clear tube to ensure a seal has formed with the bleeder screw.

    2. Repeat steps 2-5 until there are NO BUBBLES while opening and closing the bleeder screw.

    3. Move on to Step 7.

  7. If there are NO BUBBLES visible in the clear tube:

    1. Repeat steps 2-5 two more times before closing bleeder screw very tightly.

    2. Move on to the next caliper in the order, beginning again at step 1.

What should I do if brake fluid spills? (Spill Cleanup)

  1. Make anyone around the spill aware of it to avoid injury/ unecessary contact with fluid.

  2. Cover spill with absorbent from the spill kit or kitty litter to absorb the fluid.

  3. Once absorbed, sweep absorbent up and dispose of it in the trash.

What are the parts I need to know? (Brake System Overview)

More in-depth information on the brake system is available to team members here:https://nerdocs.atlassian.net/wiki/spaces/NER/pages/20348932 .

https://docs.google.com/spreadsheets/d/17HScGZaNL3dZwbOdW3LKkhMJAjhBRaSHrQFaM9hVyzc/edit#gid=4882425