Service Manual User Manual

Hydraulic System
9-17
f. Pump Inspection
1. Inspect internal pump components for wear, damage,
etc. If inner surfaces of the pump do not display an
ultra-smooth, polished finish, or are damaged in any
way, replace the damaged part. Most often, dirty
hydraulic fluid causes failure of internal pump seals
and damage to the polished surfaces within the pump
and other hydraulic system components.
2. If a dowel (5, Fig. 9– 11) or dowel-mounting hole is
damaged, replace the dowel or housing as required.
3. Examine thrust plates for wear (9), scoring, erosion,
pitting, discoloration, abrasions or other damage and
replace if necessary. The thrust plates seal the gear
set at the sides. Worn thrust plates allow internal
slippage (oil bypasses the pump). A maximum 0.002"
(0,05mm) of wear is allowable. Check the center of
the thrust plates, where the gears mesh together.
Erosion at the center of the thrust plates indicates oil
contamination. Pitted thrust plates indicate cavitation
or oil aeration. Discolored thrust plates indicate
overheating, probably due to low hydraulic oil level in
the reservoir.
4. Examine the gear set (
12
). Replace the gears as a
matched set if there is any scoring (particularly
scoring on the gear hubs), grooves or burrs on the
outside edges of teeth, or any nicks, grooves, frets or
other damage to teeth surfaces.
5. If the gear set is replaced (always replace the gears
as a set), the bushings (
6
) must be replaced. Inspect
all bushings for scoring or discoloration and replace if
necessary. Use a bushing puller (Fig. 9– 7) to remove
the bushings.
6. Examine the housings (
4
,
11
and
13
) and replace if
necessary. Place a straight edge across each bore.
Attempt to slip a 007" (0,18mm) feeler gauge under
the straight edge and into the bore. If bore expansion
is moderate, 007" (0,18mm) or less, the housing may
be reused. If wear or distortion exceeds 0.007"
(0,18mm), replace the housing and examine the gear
set (
12
) and bushings (
6
) for wear. Replace as
required.
Operating pressure pushes the gears against the
low-pressure side of the housing. As the hubs and
bushings wear, the bore increases. Excessive bore
expansion in a short period of time indicates
excessive pressure or oil contamination. If the relief
valve settings are within prescribed limits, check for
shock pressures or tampering. Check an oil sample
and the reservoir for dirt.
7. Always use new seals, O-rings, gaskets, etc. to help
ensure proper pump sealing and operation. Replace
all flexible seals, including the square “R” seal (
10
),
lip seal (
14
), backup seals (
7
) and channel seals (
8
).
g. Pump Assembly
1. Stone all surfaces with a medium grit carborundum
stone or equivalent.
Note: Carborundum is boron nitride (c-BN) with cubic or
“diamond” molecular structure. c-BN is a hard, abrasive
composition.
2. If bushings have been removed, deburr the bushing
bores with fine grit emery cloth.
3. Rinse all parts in an approved solvent. Blow dry and
wipe the parts with a clean, lintless cloth before
beginning assembly.
4. Install new bushings (
6
) in bores as required. Support
the housings so that they are square and level. Press
the bushings into the bores using the special
installation tool (Fig. 9– 9) and an arbor press. The
bushings must be flush with the casting surface after
installation. Stone and rinse the components as
described in steps 1 and 3.
5. Coat the outer edge of the new lip seal (
14
) with a
non-hardening sealant (
Permatex
®
Aviation Form-A-
Gasket No. 3 or equivalent). With the metal side of
the lip seal facing up, press the seal into the
mounting flange side of the shaft end cover with an
arbor press and a suitable lip seal driver. DO NOT
damage the lip seal. Press the seal into the housing
until the lip is flush with the housing recess. Wipe off
excess sealant.
6. Place the SEC housing (
13
), with the transmission-
mounting surface down, in a suitable holding device
or bench vise if possible.
7. Install new dowels (
5
) as required. Verify that dowels
are clean and free of burrs. Gently tap the dowels in
with a soft hammer.
8. Lubricate both new square “R” seals with clean
hydraulic oil. Insert the seals into their grooves in
each side of the gear housing (
11
).
9. Place new channel seals (
8
) into the grooves in both
thrust plates (
9
) with the flat side of the seal facing
away from the thrust plate (Fig. 9– 11).
10. Place a new backup seal (
7
) into the grooves in both
thrust plates (
9
) above the channel seals (
8
).
11. Install one thrust plate (with channel and backup
seals) into the SEC housing (
13
) so that the groove in
the thrust plate will face away from the gear housing
(
11
). The flat side of the seal should face down with
the relief groove facing the outlet side of the housing.
Model 3606 • Origin 10/99