Section VI. HYDRAULIC PUMP
inch (44.5 mm), the gear must be replaced. Replace
gear assemblies if journal surfaces are blackened.
a. The hydraulic pump supplies hydraulic oil
Shafts and gears must be replaced as assemblies.
under pressure to operate the hydraulic components.
Inspect bushings for scratches or cuts.
The gear type pump is directly driven by the engine
Minor scratches can be removed by honing in a circular
motion with a fine stone. Check to be certain sharp edge
b. Oil is drawn from the reservoir through a
between face of bushing and the outside diameter is not
suction line. The oil is then delivered to the
control valve and steering gear valve for
The bore of the bushing, which will be worn
distribution to the cylinders.
slightly oval, must not measure over 0.881 inch (22.3-
Hydraulic Pump, Removal and Disassembly
mm) at the largest reading. The length of the bushing
a. Removal. Refer to paragraph 2-12 and
must not measure under 1.055 inch (26.7-mm). If these
remove the hydraulic pump.
tolerances are not met the bushings must be replaced.
b. Disassembly. Disassemble the hydraulic
k. Wash spool valve and dry with
pump in numerical sequence as illustrated in figure 3-9.
compressed air. Valve must slide freely in and out of its
bore. Check diameter of all lands and replace spool if
any are less than 0.748 inch (18.9 mm). Clean orifices
If bushings (9 and 13) stick, tap body
with a fine wire.
on a piece of wood to prevent
Check valve spool spring for bends, cracks
marring mating surfaces. Care must
or deformation. Replace spring if free length is less than
be taken not to damage surface of
3.5 inch (88.9 mm).
m. Inspect the relief valve plunger for wear
Hydraulic Pump, Cleaning, Inspection and
and erosion. Replace if damaged.
n. Inspect relief valve spring for bends,
cracks or deformation. If free length is less than 0.80
a. Clean all metal parts in cleaning compound
inch (20.3 mm), replace spring.
solvent (Fed. Spec. P-D-680). Dry thoroughly with
b. Using a 2-inch (50.8 mm) inside
micrometer check the bushing bores near the front of
the housing. If bores measure over 1.770 inch (44.9
mm), discard the pump body.
(1) Before reassembling the pump check to be
certain all parts are clean and dry.
This is an indication that pump has
(2) Place pump body (30, fig. 3-9) face up and
install body dowels (29). Tap in place with a plastic
hammer. Coat body bores with light oil (OE/HDO).
pressure and the system must be
(3) Place new packings (15) and wear rings
checked to determine the cause.
(16) on the shoulder of rear bushings (13). Hold in place
c. Inspect parts for nicks and burs. Remove
with grease if necessary. Coat faces and bores of the
with emery cloth if possible. If damage is severe,
bushing with light oil. Be sure bushings (13) bottom in
body (30) and wear rings do not fall off. Place dowel
d. Inspect inside of bores for burs and remove
(14) in bushing holes and holding bushings (13)
with emery cloth.
together, carefully align them and slide them into the
e. Place a straightedge across the machined
mating surface of the flange. If the flange is bowed,
Do not force bushings into bores.
They must slide to the bottom of the
Bowing of flange is caused by
bore with hand pressure.
excessive pressures and the cause
(4) Coat gear shafts and gear faces lightly with
must be determined before installing
oil (OE/HDO). Turn pump body so that bore for spool
(28) is to the left and place drive gear (11) in top bore
Hone flange mating surface to remove
and idler gear (12) in lower bore.
burs, scratches or other damage. Clean thoroughly.
(5) Position front bushing dowel pin (10)
g. Inspect drive gear and idler gear for
between bushings (9), hold bushings together and
damaged or worn splines or gear teeth. Remove burs
with a fine hone.
h. If length of gear is less than 1.320 inch
(33.5 mm) or if gear outside diameter is less than 1.754