Hydro-Boost
The Bendix Hydro-Boost brake booster is a hydraulically operated brake booster powered by the power steering pump. The power steering pump provides the fluid pressure to operate both the hydraulically-powered brake booster (hydro-boost) and the power steering gear. It provides a variable power assist that is regulated by the brake pedal application pressure.

The hydro-boost also has a reserve system (compressed gas accumulator) that is designed to store sufficient fluid under pressure to provide at least two power assist brake applications in the event that the fluid flow from the power steering pump is not available. The brakes can also be applied manually if the reserve system is depleted.

Hydro-Boost model identification is stamped into the booster housing near the inlet line.

Bleeding the Hydro-Boost Unit

1. Fill the pump reservoir with Motorcraft Mercon® Multi-Purpose Automatic Transmission Fluid E4AZ-19582-B XT-2-QDX or -DDX (ESP-M2C138-CJ) or equivalent. F-Super Duty Motorhome and Commercial Stripped Chassis uses a ZF pump and Motorcraft Mercon® lubricant only.
2. Crank the engine for several seconds, with the coil wire disconnected (do not start the engine).
3. Check the fluid level, and add if necessary. Reconnect coil wire.
4. Start the engine.
5. With the engine running, turn the wheels lock to lock two times. Turn the engine off.
6. Depress the brake pedal several times to discharge the accumulator.
7. Repeat Steps 4 and 5.
8. If foaming occurs, stop the engine and allow the foam to dissipate.
9. Repeat Steps 4 and 5 as required, until all the air is removed from the system.

NOTE: The Hydro-Boost is generally self-bleeding, and the above procedure will normally bleed the air from the booster. Normal operation of the vehicle will further remove any additional trapped air.

For disassembled photos, see this post.
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Owner caption January 2006 · Photo 1154 of 5000