Power Brake Assist: Service and Repair

Certain general service procedures apply, regardless of whether the brakes are vacuum or hydraulically assisted. Only top quality, clean brake fluid should be used. More seals and valves are used with power brake systems than with ordinary brakes, so an inferior brake fluid will do much more damage. For the same reason, be sure all dirt is kept out of the system. Additionally, on models with hydraulic assist brakes, care must be taken not to mix the fluids of the booster hydraulic system and brake hydraulic system as the fluids are not compatible.
If the power unit fails, the brakes will still operate, as the conventional brake system is left intact and a power unit is simply added to the existing system. Troubleshooting is then exactly the same up to the power unit. As with conventional hydraulic brakes, a spongy pedal with power brakes is caused by air in the system and grease on the linings will cause the brakes to grab. However, power brakes develop higher line pressure, thus making leaks more critical.
Power units do not require adjustment. If there is a problem, the various valves and connections are simply replaced. The only exception is that the power units themselves sometimes have an adjustable connection to the brake pedal or linkage.