The brake pedal moves down slowly with the pedal force remaining constant
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 (the engine cooling fan will turn on twice).
2. Attach a piece of special tape used for painting, approximately 50 mm long, to the steering column under the steering wheel. Make a horizontal mark on the tape.
3. With the gearbox in Neutral position, lightly press and hold the brake pedal (approximately the same amount of pressure is required to keep a car with an automatic transmission from moving), then release the parking brake lever.
4. While holding the brake pedal, attach the end of a metal tape measure to the pedal, then pull the tape measure to the steering wheel. Note the distance between the brake pedal and the mark on the steering wheel.
5. Maintain constant pressure on the brake pedal for 3 minutes.
6. Measure which division the applied mark now corresponds to.
If the distance is 10 mm or less, the master cylinder is OK.
If the distance is more than 10 mm, the master cylinder must be replaced.