How to Repair a Leaky Brake Master Cylinder

A red and black car on the road.
What You'll Need
Wrench and socket set
Turkey baster
Can or bucket
Work table
Vacuum hose
Protective gear (working glove and eye goggles)

If brake fluid is leaking from the brake master cylinder and dripping on bolts and the booster, then repair it as soon as the problem is noticed. It is essential to have it working in good condition as it controls the brake warning lights and it is responsible for the good condition of the brake pedal. It is possible to change and repair a master cylinder at home.

Step 1 - Position the Car

Park the car in a manner so as to provide enough working space. Take care and pay attention when working with brake fluids. It easily removes paint and it can be a health hazard. Do not inhale or bring it into contact with your eyes.

Step 2 - Remove Brake Fluid

Open the cap on the master cylinder, and carefully suck the fluid using a syringe or turkey baster and drain it in the can or bucket. Remove as much fluid as possible.

Use wrenches to disconnect the lines from the metal pipes. Take care not to use too much force to avoid damaging the lines. However, if they are too worn out then consider replacing them with new ones. It is advisable to place a bucket or can at the bottom part of the car so as to minimize spillage.

Step 3 - Remove Master Cylinder

Obtain the socket set and loosen the two bolts holding the master cylinder to the booster. Carefully remove the nuts using hands and place them in a safe position. Remove the master cylinder of the engine and place it on a work table.

Step 4 - Repair Leak

Inspect the master cylinder to establish the point at which it is leaking. Look out for a loose or damaged cap; check the condition of the diaphragm too. If the problem is extensive and the master cylinder is worn out, replace it with another one.

If the problem lies with a loose cover or cup, or if it is cut, cracked, or deformed, then replace them with new ones.

Step 5 - Bleed Master Cylinder

Once the master cylinder is repaired, clamp it on a work table to bench bleed it. Remove plugs from line fittings on the master cylinder and fill the reservoir with about 1/3 of brake fluid.

Use a screwdriver to push the piston on the master cylinder until the fluid comes out with bubbles. Repeat the process until the bubbles decrease in size and finally disappear.

Step 6 - Reinstall the Master Cylinder

Carefully reattach the master cylinder to the brake booster and fasten it using bolts. Replace all the other components and make sure they are fixed correctly and securly.