Step by step guide on how to replace a brake master cylinder, This article pertains
to most cars.
Difficulty Scale: 3 of 10
Tool and Supplies Needed
- Replacement brake master cylinder
- Brake fluid
- Line wrench set
- Show towels
- Socket set
- Protective gloves and eye wear
Begin the car on level ground, in park, with the emergency brake set.
Brake Master Cylinder
- Begin by removing brake fluid reservoir
cap and insert brake fluid removal tool (turkey baster), remove as much brake fluid
as possible, then reinstall cap.
Brake Fluid Removal
- Remove the electrical connector to the
fluid level sensor. Most connectors have safety clips that need to be released before
they will disconnect.
Removing Brake Fluid Warning Light Connector
- Install a line wrench firmly on the brake
fluid lines departing from the master cylinder. A line wrench is a special wrench
that holds five points of the fitting as opposed to two points like a normal wrench,
which gives this style wrench more power without damaging fittings like a normal
wrench. Apply force to the wrench in a counter clockwise motion to loosen and remove
fitting and line in the master cylinder. Repeat operation until all fluid lines
are removed. (Note: Brake fluid will leak from brake lines when removed.)
Removing Brake Fluid Lines
- Insert socket wrench onto master cylinder
mounting bolts. After mounting bolts are removed, lift the master cylinder off the
mounting studs and out of the vehicle.
Brake Master Mounting Bolts
- Reinstall master cylinder, tighten master
cylinder mounting bolts and reconnect the fluid lines and fluid level sensor. Refill
the master cylinder with new fluid most cars use DOT3 or DOT4. Once the master cylinder
is full loosen all four brake fluid bleeder screws on the brake calipers or wheel
cylinders. Next, press the brake pedal down completely, while holding the brake
pedal down have a helper close all four brake bleeder screws. Then, allow the brake
pedal to return to normal position slowly, this will draw new fluid into the master
cylinder body. Continue this procedure until the brake fluid is clean with no air
bubbles out of each bleeder, close all bleeders and refill the master cylinder with
brake fluid to the proper level. Do not drive vehicle if normal brake pedal operation
is not present. Visit -
Brake system bleed
Reinstall New Brake Master Cylinder
The brake master cylinder is the manual hydraulic pressure part of the brake
system. The brake master holds hydraulic brake fluid that is used to actuate the
brake system. Brake fluid flows through brake system components and then to the
front brake caliper under pressure to slow the vehicle. When a master cylinder fails
a low brake pedal is experienced. The master cylinder is divide into two separate
sections, a primary and secondary pressure system. This safety system was created
inside the master cylinder: if one half of the brake system fails you will still
have the remaining half to help slow the vehicle. Inspect for brake fluid leakage
around the master cylinder and check for proper fluid level regularly. If leakage
is present replace master cylinder immediately.
- Master cylinder fails, illuminating the brake warning light.
- Master cylinder leaks fluid, illuminating the brake warning light.
- Master cylinder actuator rod is adjusted out too far, not letting the brake
master plunger to return creating residual brake pressure causing the brakes
- Always use brake fluid from a closed container to avoid moisture contamination.
- Check brake shoe adjustment (drum brakes only).
Article first published 2016-02-03