Brake pedal moves slowly down with constant pedal effort
1. Set the parking brake and start the engine, then turn off the air conditioner. Allow the engine to warm up to normal operating temperature (engine cooling fan will turn on twice).
2. Attach to the steering column under the steering wheel a piece of special tape used in painting work, approximately 50 mm long. Put a horizontal mark on the tape.
3. With the transmission in Neutral, lightly depress and hold the brake pedal (about the same amount of pressure is needed to keep a car with automatic transmission from moving), then release the parking brake lever.
4. While holding the brake pedal, attach the end of a metal tape to the pedal, then pull the tape out to the steering wheel. Pay attention to the distance between the brake pedal and the mark on the steering wheel.
5. Maintain the same force applied to the brake pedal for 3 minutes.
6. Measure which division the marked mark now corresponds to.
If the distance is 10 mm or less, then the master cylinder is good.
If the distance is more than 10 mm, then the master cylinder must be replaced.