TROUBLESHOOTING THE HMMWV - OD1616 - LESSON 1/TASK 1
The vacuum booster depends on manifold vacuum and
atmospheric pressure for its assist power.
The unit's smaller size
has made it easier to fit in the engine compartment and has
eliminated the need for a remote or frame-mounted booster previously
used on some applications.
The hydro-boost system consists of a booster assembly, accumulator,
The booster itself
consists of an open center spool valve and sleeve assembly, lever
assembly, input rod assembly, power piston, and an output push rod.
The booster assembly is mounted to the vehicle in much the same
manner as a normal vacuum booster. The pedal rod is connected to the
booster input rod end.
The master cylinder is located at the
opposite end of the booster. The booster's output push rod fits into
which is unmodified except for a larger reservoir and an additional
return port for the hydro-boost return line, supplies the hydraulic
pressure to the hydro-boost unit through external lines.
When the engine is running, the fluid enters the unit through the
pump port where the majority of the fluid is directed to the gear
port and then to the steering gear by an external line.
quantity of power steering fluid that did not go to the power
steering gear circulates inside the hydro-boost unit and then returns
to the steering pump reservoir by an external line.
Hydro-boost Accumulator Operation.
The hydro-boost unit includes a
reserve brake system that makes available two or three power-assisted
brake applications in the event that the flow of fluid from the power
steering pump is interrupted by a stopped engine, broken belt, pump
failure, ruptured hose, etc.
This system uses a gas accumulator to
store fluid under gas pressure.