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Hydro-Boost Leak
Basic Test

With the engine off, depress and release the brake pedal several times to deplete all hydraulic pressure from the Hydro-Boost. Depress and hold the brake pedal with light pressure, then start the engine. If the Hydro-Boost is operating, the pedal will fall slightly and then hold. Less pressure will be required to hold the pedal at this position.

Hydro-Boost Leak Test

Thoroughly clean the Hydro-Boost unit, and all hoses and hose connections. Start the engine and run at idle speed. If the hose connections do not leak, check the Hydro-Boost for leakage. Apply the brakes with approximately 444 N (100 lbs) pressure at the pedal, and hold while checking the Hydro-Boost hoses for leaks. CAUTION: Do not hold the brake pedal at 444 N (100 lbs) effort for more than five seconds at a time. If the Hydro-Boost leaks, it is worn or damaged and must be replaced.

Reserve Retention Check

Charge the system with pressure by holding the steering on the stop, or by holding the brake pedal with 444 N (100 lbs) of force for five seconds with the engine running at idle. Turn the engine off. Eight to twelve hours later, depress the brake pedal with the engine off. There should be some degree of power reserve. If there is no power reserve, replace the Hydro-Boost unit.

Brake Hydraulic Leak Test

Depress and release the brake pedal several times, then hold the brake pedal down with medium pressure of 111-156 N (25-35 lb). If the pedal falls away, the brake system is leaking. Check for leaks at the disc brake calipers, brake lines, master cylinder, and hoses. If there is no external leakage, there may be internal leakage in the master cylinder. If the pedal does not fall away during this test, then the hydraulic system is not leaking.

For disassembled photos, see this post.