Audi A4 B7/B8: How to Replace Brake Master Cylinder
The master cylinder is what pumps the brake fluid into your brake system. Read on to learn how to replace it in the Audi A4 B7/B8.
This article applies to the Audi A4 B7 and A4 B8 (2004-2015).
The master cylinder is the device in your Audi A4 B7/B8 that converts brake pedal pressure to hydraulic pressure and pumps the brake fluid through your system. The master cylinder can fail when one if its seals becomes compromised, or is generally unable to produce enough pressure. A bad master cylinder will be accompanied by a spongy brake pedal. Replacing the master cylinder also requires you to drain the system of brake fluid, and obviously refill the system as well as bleed it of air when you're done. The process isn't too hard, but it requires some work and time. If you have a bad master cylinder and you're up for the task, read on to learn how to replace it.
Materials Needed
- Socket
- Turkey baster
- Wrench
- Hose
- Bottle
- Brake fluid
- Master cylinder
Step 1 – Suck old fluid out of master cylinder
Use your turkey baster to suck the old fluid out of your master cylinder until it's empty.
Step 2 – Disconnect all connections
Before removing the master cylinder, disconnect the electrical connection from the master cylinder. Then use your wrench to disconnect the two lines connected to it. Residual brake fluid is going to leak out, so have some shop towels and rags handy.
Step 3 – Replace master cylinder
The master cylinder is held in place by two nuts that are connected to the brake booster's studs. Remove the two nuts, then pull the master cylinder out. Install the new master cylinder the same way, tighten the nuts, then connect the two lines and the electrical connection.
Step 4 – Add fluid and bleed the system
Fill the new master cylinder with brake fluid until the max line. Pump the brake pedal a few times to distribute some fluid through the system.
We will next have to bleed the system of excess air. To bleed the system, you will have to purge the residual brake fluid and trapped bubbles from the brake calipers. Always start at the caliper furthest away from the master and work your way towards it. That means going in the following order: passenger-rear, driver-rear, passenger-front, and driver-front. Begin by locating the bleeder on the rear of the calipers, and attach a piece of clear tubing the nipple, with a catch can on the other end to catch old brake fluid. Ask a friend to pump the brake pedal a few times, then keep it pressed down. With the brake pedal pressed down, loosen the bleeder screw using your wrench. Close the valve after a few seconds and repeat that process several times. Once you stop seeing bubbles in the fluid that is draining out, tighten the bleeder screw first, then let go of the brake pedal. Repeat the process for the rest of the calipers, but make sure you add brake fluid into the master cylinder between each caliper.
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