RAM 3500 Truck 2WD V10-8.0L VIN W MDC (1999)
Hydraulic Brake Booster: Description and Operation
DESCRIPTION
Hydraulic Brake Booster
Vehicles equipped with a Hydraulic Booster use the booster to supply power assist to the brake system. The booster is mounted to the front cowl panel
on a bracket. The master cylinder is mounted to the front of the booster.
The hydraulic pressure is supplied to the booster from the power steering pump. The pressure line from the pump is connected to the booster. From
the booster a second pressure line is connected to the steering gear. Return lines from the booster and steering gear are connected to the power steering
pump reservoir.
A nitrogen charged pneumatic accumulator on the booster provides reserve power assist pressure. If power steering pump pressure is not available
(broken belt/pump failure) the accumulator reserve pressure is used. This provides 2 or 3 stops at partial boost.
OPERATION
Brake Pedal Released
With the brake pedal released most of the hydraulic fluid is routed through the booster power section and to the steering gear. A portion of the fluid is
diverted into the booster power section, then returns to the power steering pump reservoir.
Brake Pedal Depressed
With the brake depressed, the input rod and piston move forward. This causes the lever assembly to move the sleeve forward to close off the holes
leading to the open center of the spool valve. A small additional lever movement, moves the spool valve forward in the spool valve bore. The spool
valve then diverts some hydraulic fluid into the cavity behind the booster piston building up hydraulic pressure. This hydraulic pressure moves the
piston and output rod forward. The output rod moves the primary and secondary master cylinder pistons which applies hydraulic pressure to the brake
system. When the brake pedal is released, the spool and sleeve assembly returns to it's normal position. Excess fluid behind the piston returns to the
power steering pump reservoir through the return hose.
Manual Brake Application
The system is designed to permit manual brake application in the event hydraulic pressure is interrupted. A somewhat greater pedal effort is required
to apply the brakes manually.