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 you may experience a
low brake pedal, the master
cylinder is divide into two separate sections, the primary and secondary pressure
systems. This system was created inside the master cylinder for safety; if one half
of the brake system fails you will still have the remaining half to help slow the
vehicle. Note: You must know how to
bleed a hydraulic
brake system before you can service or change a master cylinder.
Step 1 - Identify Brake Master Cylinder and Reservoir
Brake Master Cylinder
Identify brake master cylinder components,
brake fluid cap, brake master cylinder,
fluid lines, and brake fluid level sensor. Inspect for any brake fluid leakage around
the master cylinder and check for proper fluid level regularly. If leakage is present
replace master cylinder immediately.
Step 2 - Removing Brake Fluid
Brake Fluid Removal
Remove brake fluid reservoir cap and insert brake fluid removal tool, remove
as much brake fluid as possible. Then refill and reinstall brake fluid reservoir
cap.
Step 3 - Removing the Brake Fluid Level Sensor Connector
Brake Fluid Warning Light Connector
Remove the electrical connector to the fluid level sensor. Most connectors have
safety clips that need to be released before they will disconnect.
Step 4 - Removing Brake Fluid Lines
Brake Fluid Lines
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 special wrench more
power without damaging the fitting than 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.
Step 5 - Removing Master Cylinder Mounting Bolts
Brake Master Mounting Bolts
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.
Step 6 - Reinstall and Bleed Master Cylinder System
New Brake Master Cylinder
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 but you should consult the cap on the master cylinder
or your owner's manual or
repair manual. Once
the master cylinder is full loosen all four brake fluid bleeder screws on the brake
caliper or wheel cylinder. Next, press the brake pedal down completely, while holding
the brake pedal down have a helper close all four brake bleeder screws. Now 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.
CAUTION: DO NOT DRIVE OR MOVE A VEHICLE UNTIL NORMAL BRAKE
PEDAL OPERATION IS PRESENT!
Common Problems:
- Master cylinder fails illuminating the
brake warning light
- Master cylinder leaks fluid illuminating the brake warning light
- Master Cylinder actuator rod is adjusted out to far not letting the brake
master plunger not to return all the way creating residual brake pressure causing
the brakes to drag
If further assistance is needed, our certified car repair technicians are ready
to answer your car questions. Also, gain manufacturer
specific instructions and information by clicking -
Auto Repair Manual
Related Car Repair Information
