TOPIC 1. HYDRAULIC PUMP

TM 10-3930-644-14&P

HYDRAULIC SYSTEM

TOPIC 1. HYDRAULIC PUMP

A. DESCRIPTION

stick, tap body on a piece of wood to prevent

marring mating surfaces. Place bushings on

The hydraulic pump (Fig 1-1) is a gear type unit driven

clean rag to prevent damaging surfaces.

directly from the engine. With this type of installation,

the pump is always driven at engine speed.

NOTE

If the front bushings are excessively

The hydraulic pump consists of a housing, a combination

tight and difficult to remove, it

end plate and mounting flange, gears, seals, bushings

indicates operation with dirty oil.

and capscrews. The housing also contains bores for the

priority flow control valve, and the priority flow relief

5. Set pump body face-up and remove drive shaft

valve.

and idler shaft.

The relief valve pressure setting can be adjusted by

6. Invert pump body and allow rear set of bushings

turning the setscrew, located in the end of relief

to slide out. See Step 4.

assembly, in or out. Turning the setscrew IN increases

the spring pressure on the cone to increase the relief

7. Remove the relief port plug and remove the

pressure setting, while turning the setscrew OUT will

relief valve components, laying them out in their

decrease the relief pressure.

order of removal.

When the hydraulic pump must be removed for

8. Remove plug from rear of body and take out

replacement or repair, the following procedure is

steering spool and spring.

recommended:

9. Wash parts in solvent, blow dry

with

B. REMOVAL

compressed air and inspect for damage.

1. Remove radiator grille and components

D. INSPECTION

necessary to gain access to hydraulic pump.

1. Check bushing bores near the front of the

housing, using a 2" inside micrometer. If bores

NOTE

measure over 1.770, discard the pump body.

On truck applications where the

This indicates pump has been subjected to

hydraulic oil reservoir is below the

excessive pressures, and the system should be

supply line connection at the pump, it

checked to determine the cause.

will not be necessary to drain the

reservoir. Check reservoir to see if

2. Measure depth of grooves cut by the gears. If

oil level is above or below the pump.

deeper than .005", it results in reduced flow of

If it is above the pump, oil will flow

hydraulic oil. The gear track should have a

out of the supply (suction) line, when

smooth texture radially and should be darker

it is removed from the pump.

color than the rest of the body. If it has a

2. Disconnect hoses from fittings on hydraulic

sandpaper like texture, and a light gray or silvery

pump, and cap hoses to prevent contamination.

color (when dry), it indicates pump has been

running on dirty or foamy oil. Flush hydraulic

3. Remove capscrews and lockwashers attaching

system before installing clean oil, and if puma

pump bracket to the engine and remove pump

body is to be reused, hone the face flat with a

assembly.

fine stone and clean thoroughly; use a fine

sandpaper to remove any burrs left inside the

4. Place the hydraulic puma assembly in a suitable

bores.

work area for service.

3. Inspect the shaft seals in the end plate, and if

C. DISASSEMBLY

they are not damaged or have not been leaking,

they can be reused.

Place a straightedge

1. Thoroughly clean outside of pump.

across the machined surface that faces the

pump body. If the flange is bowed, do not

2. Remove capscrews which attach mounting

reuse.

flange to pump body. Remove flange.

NOTE

3. Remove all accessible O Rings and backup

Bowing of flange is caused by

rings.

excessive pressures, and the cause

should

determined

before

4. Turn pump over, holding one hand over the front

reinstalling the pump.

bushings and let them slide out. If bushings

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