See Figures 1, 2 and 3
A hydraulically powered brake booster is used on the F-Super Duty truck. The power steering pump provides the fluid pressure to operate both the brake booster and the power steering gear.
The Hydro-Boost assembly contains a valve which controls pump pressure while braking, a lever to control the position of the valve and a boost piston to provide the force to operate a conventional master cylinder attached to the front of the booster. The Hydro-Boost also has a reserve system, designed to store sufficient pressurized fluid to provide at least 2 brake applications in the event of insufficient fluid flow from the power steering pump. The brakes can also be applied unassisted if the reserve system is depleted.
REMOVAL & INSTALLATION
See Figure 4
- Remove the master cylinder from the Hydro-Boost unit. Do not disconnect the brake lines from the master cylinder! Position the master cylinder out of the way.
- Disconnect the 3 hydraulic lines from the Hydro-Boost unit.
- Disconnect the pushrod from the brake pedal.
- Remove the booster mounting nuts and lift the booster from the firewall.
Installation is the reverse of removal. Tighten the booster mounting nuts to 25 ft. lbs. (34 Nm); the master cylinder nuts to 25 ft. lbs. (34 Nm); connect the hydraulic lines, refill and bleed the booster as follows:
- Fill the pump reservoir with Dexron®II ATF.
- Disconnect the coil wires and crank the engine for several seconds.
- Check the fluid level and refill, if necessary.
- Connect the coil wires and start the engine.
- With the engine running, turn the steering wheel lock-to-lock twice. Shut off the engine.
- Depress the brake pedal several times to discharge the accumulator.
- Start the engine and repeat Step E.
- If foam appears in the reservoir, allow the foam to dissipate.
- Repeat Step E as often as necessary to expel all air from the system.
The system is, in effect, self-bleeding and normal vehicle operation will expel any further trapped air.