Brake Booster

All models are equipped with a dual-diaphragm vacuum booster. Boosters are self-contained, vacuum power brake units. Booster assists in actuating master cylinder push rod.

Booster contains a dual vacuum-suspended diaphragm which uses engine manifold vacuum or atmospheric pressure for power. Diesel models use a belt-driven vacuum pump to provide vacuum for booster actuation.

A mechanically operated booster check valve controls power brake application and release in relation to pressure applied to check valve operating rod. Booster check valve is the only serviceable component of brake booster assembly.

An equalizer valve links 2 chambers of brake booster. When valve opens, vacuum in chambers can equalize. When it closes, chambers are separated. A vacuum bleed valve functions to reduce amount of vacuum in secondary chambers when boost is required.

Excursion and Super Duty Pickup uses a Hydro-Boost system. Hydro-Boost is hydraulically operated by power steering pump and provides a variable power assist regulated by brake pedal pressure. Hydro-Boost has a reserve system (compressed gas accumulator) which stores enough fluid under pressure to provide at least 2 power-assisted brake applications if power steering pump fluid flow stops. Brakes can also be operated manually if reserve system is lost.

Hydro-Boost power units in normal condition produce certain noises. These noises occur when brakes are used more than usual. In general, these noises are hissing, clunks, clicks and chattering. Hydro-Boost hisses when greater than normal braking effort is used. Hissing increases when pedal effort and operating temperatures increase. Loud hissing at normal pedal effort of 25-35 lbs. (11-16 kg) or less should be investigated. Clunk, chatter and clicking noises are heard when brake pedal is quickly released from hard braking.