1998 Lexus SC 400 Owners Manual - Page 192

STARTING AND DRIVING BRAKE SYSTEM The tandem master cylinder brake system is a hydraulic system with two separate sub-systems. If either sub-system should fail, the other will still work. However, the pedal will be harder to press, and your stopping distance will be longer. Also, the brake system warning light may come on. CAUTION Do not drive your vehicle with only a single brake system. Have your brakes fixed immediately. Brake booster The brake booster uses engine vacuum to power-assist the brakes. If the engine should quit while you are driving, you can bring the vehicle to a stop with normal pedal pressure. There is enough reserve vacuum for one or two stops but no more! CAUTION D Do not pump the brake pedal if the engine stalls. Each push on the pedal uses up your vacuum reserve. D Even if the power assist is completely lost, the brakes will still work. But you will have to push the pedal hard - much harder than normal. And your braking distance will be longer. 175