We are a team of ASE certified mechanics that have created this guide to show
you why your brake master cylinder is not working and what you can replace it.
How Does it work?
The brake master cylinder is the hydraulic pressure part of the brake
system which holds brake fluid in a reservoir. When you push the brake pedal
down the plunger inside the brake master cylinder housing is forced forward
which transfers pressurized fluid to the brake calipers or wheel cylinders which
then actuates the brake system to slow the car down. The master cylinder is
divided into two separate sections, a primary and secondary pressure system.
This safety system was created inside the master cylinder so if one half of the
brake system fails the car will still have the remaining half to help slow the
vehicle. This safety is divided into front or rear brakes.
What Goes Wrong?
The master cylinder is constructed with rubber seals which in time can go bad
and allow the brake fluid to bypass internally or leak out from the rear of the
master. When the brake master goes bad the brake pedal will sink and the brake
warning light will come on. This condition will greatly decrease the stopping
ability of the car. Inspect for brake fluid leakage around the master cylinder
and check the fluid level regularly. If leakage
is present replace master cylinder immediately. If the master cylinder actuator rod is adjusted to far
out it will not allow the brake master plunger to fully return creating residual brake pressure which causes the brakes
to lock up and not allow the car to roll. There must be 1/16 of an inch or
1.5 mm clearance between the master cylinder and the brake booster or pedal rod.
How Much Does It Cost?
If you are having the job done at a repair garage or a dealership you can
expect to pay between $270.00 and $380.00 dollars (US). There are two kinds of
replacement master cylinder's, rebuild and new. We recommend a new unit simply
because the brake system is a vital part of your car's safety. A new master
cylinder will cost between $35.00 and $75.00 dollars (US) at Amazon or your
local parts store. Brake fluid will cost about $4.00 and the bleeder kit about
How Long Do Brake Master Cylinders Last?
Because the brake master has rubber seals which are used every time you hit
the brakes this part is a normal wear item which will last between 70,000 and
110,000 miles depending on driving habits and conditions such as hard braking
along with stop and go traffic.
Park the car on level ground with the engine off and the emergency brake set.
You will be dealing with brake fluid so wear eye protection and gloves. Brake
fluid is corrosive to paint so if you get any on the cars finish quickly wash it
with soap and water. Only use brake fluid from a seal container to avoid
moisture contamination which can damage the brake system.
Tool and Supplies Needed
New brake master cylinder
Protective gloves and eye wear
Soap and water
Raise the hood to identify the master cylinder location which is usually on
the fire wall on the driver's side. There will be two or four brake lines
connected the main body of the master and a small wiring connector attached to
the brake fluid reservoir.
Remove the Master Cylinder: You will want to remove as much of the old
brake fluid as possible to avoid spillage during the removal. Begin by removing fluid reservoir
cap and insert a turkey baster to remove the fluid and then reinstall cap.
Release the safety clip of the electrical connector and gently pull it from
the fluid level sensor in the reservoir.
Use a line wrench
and firmly secure it on the brake fluid lines to remove them. These line wrench sizes are usually 13mm, 14mm, 15mm
or 16mm. Apply force to the wrench in a counterclockwise motion to loosen and remove
the line fitting. Repeat the operation until all fluid lines are removed. These
lines can be fairly tight so be ready. As you loosen the lines brake fluid will
start to leak out. You can install a shop towel below the master to catch the
fluid and then discard the towel once the job is completed.
Once all of the lines have been removed use a wrench or socket to loosen and
remove the master cylinder mounting bolts. These nut sizes are usually 14mm or
15mm. After all mounting bolts are removed push the master forward and
then lift it off the mounting studs and then out of the engine compartment. Have a shop towel ready
for the removal to stop dripping brake fluid from potentially getting on the
Reinstall the New Master Cylinder: Before the new master cylinder can
be installed it must be bunch bled. Hold the master cylinder in a vise so it
doesn't move. Then remove the fluid lid of the reservoir. Remove the dust caps
that cover the line holes of the master. Then install the master cylinder
bleeder kit which is two or four plastic fittings and rubber hoses which will be
connected to the fittings and then routed back into the fluid reservoir. Make
sure the lines are far enough into the reservoir as to not suck in air. Fill the
master reservoir with brake fluid. Use a large Phillips screw driver and place
it at the rear of the master and into the plunger. Now start pushing the plunger
into the master. Air bubbles will start to come out of the rubber lines inside
the reservoir as you press inward. Once the plunger is completely in release the
screwdriver (slowly) which will draw fluid into the master as you watch the
brake fluid level go down in the reservoir. Continue this operation until no air
bubbles are present. Refill the reservoir as needed to retain the fluid level.
Once completed remove the bleeder kit and reinstall the reservoir cap. A small
amount of fluid will start to leak out. Use a shop towel to help guard against
paint damage as you reinstall the brake master back into the car. Slide the
master back over the booster studs and reinstall the mounting nuts finger tight.
While the master is still a little loose reinstall the brake lines, this will
help in the line installation. Use a regular wrench to snug up the lines to stop
the master from leaking additional fluid. Never allow the brake fluid to drain
completely out of the master. If the fluid runs completely out of the master it
will need to be re-bled. Once the mounting bolts have been fully tightened use a
line wrench to put the final tighten on the brake lines. The torque spec on the
master cylinder's mounting bolts is usually between 35 and 45 foot pounds.
Reconnect the fluid level sensor and refill the master cylinder with fluid and
reinstall the cap.