Internal Leak Test

Start engine and allow it to idle.
Apply light, steady pressure to the brake pedal. Observe both the brake pedal feel and travel.
Release brakes and turn OFF the ignition.
If brake pedal apply felt spongy, but brake pedal travel was not excessive, perform the following steps:
- Inspect brake system for external leaks. See EXTERNAL LEAK TEST .
- Pressure bleed the brake system in order to purge any air that may be trapped in the system. See BLEEDING BRAKE SYSTEM .
If the brake pedal apply did not feel spongy, but the brake pedal travel was excessive, perform the following steps:
- Loosen master cylinder-to-brake power booster mounting nuts.
- Carefully pull master cylinder away from brake power booster just enough to inspect the mounting surface of the master cylinder.
- Inspect master cylinder mounting surface at the primary piston for brake fluid leaks.
If master cylinder exhibits any leakage around the primary piston, then the primary piston primary seal and/or secondary seal is leaking and the master cylinder requires overhaul or replacement.
If master cylinder primary piston does not exhibit any leakage, pressure bleed brake system. See BLEEDING BRAKE SYSTEM .
If brake pedal apply did not feel spongy and brake pedal travel was initially steady and not excessive, but then gradually fell, then master cylinder requires overhaul or replacement due to an internal leak past the secondary piston from the secondary piston primary seal or secondary seal.
If the brake pedal apply did not feel spongy, and the brake pedal travel was initially steady and not excessive, then fell slightly, then became steady again, then the Brake Pressure Modulator Valve (BPMV) may be leaking internally, and may require replacement.