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NOTICE: When fasteners are removed, always reinstall them at the same location from which they were
removed. If a fastener needs to be replaced, use the correct p art num ber fastener fo r that application. If
the correct p art num ber fastener is n ot available, a fastener o f equal size and strength (o r stronger) may
be used. Fasteners that are n ot reused and those requiring thread locking com pound w ill be called out.
The correct torque value m ust be used when installing fasteners that require it. If the above conditions
are n ot followed, parts o r system damage could result.
NOTICE: The hydraulic booster operates on pow er steering fluid. Brake flu id m ust n ot be allowed to enter
the booster p orts o r come in contact with the booster components. Hands and tools m ust be clean and
free Of a ll traces o f brake flu id o r other contam inants before servicing the booster. Fluid interchange o r
contamination will cause swelling and deterioration of the seals and rubber parts.
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This section covers the unit repair procedure for the
Delco Moraine Hy-Power brake booster.
The hydraulic booster is a device that applies force to
the master cylinder when the brake pedal is applied.
The fluid flowing through the booster head is controlled
by brake pedal movement.
Fluid from the power steering pump enters the boost
er at the inlet port, flows through the control valve and
seat, leaves through the outlet port and flow switch, and
returns to the power steering pump.
The hydraulic booster cylinder rod attaches to
ton that contains the control valve seat. This assembly
moves when brake pedal pressure is applied. As the
control valve moves closer to the control valve seat in
the piston, it restricts fluid flow and builds pressure on
one side of the piston. The pressure overcomes the
return spring and moves the piston to a balanced posi
tion. The piston is balanced when the pressure from the
return spring on one side equals the pressure of the
hydraulic fluid flowing through the control valve and
seat. As the piston moves, it pushes the cylinder rod
and applies pressure to the master cylinder.
SECTION 5D2
HYDRAULIC BOOSTER
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GENERAL DESCRIPTION
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HYDRAULIC BOOSTER 5D2-1
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A relief valve inside the booster head limits the pres
sure to 4826 kPa (700 psi) which limits brake line pres
sure at the master cylinder to 13455 kPa (1950 psi).
This pressure level provides good braking without dam
aging the brake pipes Or hoses. When actuated, the
relief valve allows fluid to bypass the piston. Fluid con
stantly flows through the booster head when the engine
is running.
An electro-hydraulic (EH) pump (32) is used as a
back-up to the belt driven power steering pump. The
pis
EH pump turns on when fluid stops flowing through the
booster head. The EH pump is a small hydraulic pump
that mounts to the bottom of the booster head. -
The EH pump draws fluid from the low pressure side
of the booster head piston and delivers it to the high
pressure side. The normal output of the EH pump is
2070-2415 kPa (300-500 psi), about one-half that of the
power steering pump.
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An aluminum ID tag is attached to the lower front Side
at the electro-hydraulic pump bracket.
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