Chapter 4. REPAIR OF HYDRAULIC SYSTEM

CHAPTER 4

REPAIR OF HYDRAULIC SYSTEM

Section I. HYDRAULIC SYSTEM

(9) Remove plug (15) and remove relief valve

4-1. General

parts (10 through 14).

In this equipment all lifting, tilting, and steering units are

c. Cleaning and Inspection.

operated by means of hydraulic pressure. Service and

NOTE

adjustment of the hydraulic system is described in TM

10-3930-618-20. This section will cover direct and

All parts should be thoroughly

general support maintenance of the hydraulic system

cleaned in cleaning solvent (Spec. P-

components.

S-661) and dried with compressed air

before inspection. After inspecting,

4-2. Pump Assembly

reclean serviceable parts, apply a

a. Removal. Refer to paragraph 2-10 for hydraulic

coating of oil and wrap the parts in

pump removal.

clean, lint-free cloths until the pump

NOTE

is reassembled.

Clean outside of pump prior to

(1) Clean in accordance with above note.

starting disassembly.

(2) Using a 2-inch inside micrometer,

b. Disassembly.

measure bore in body (18) near the front. The bore

(1) Remove screws and separate flange from

diameters should not exceed 1.770 inch.

pump body (fig. 4-1).

(3) It is normal for gears to cut shallow

NOTE

grooves with tips of teeth on the inlet side. Measure

To prevent chance of leakage at

depth of groove cut by idler gear (26), which will be

reassembly, avoid scoring or nicking

slightly deeper than groove cut by drive gear (25).

of mating cover, housing, and

Discard body if groove depth exceeds 0. inch.

(4) Normal grooves (tracks) have a smooth

adapter machined surfaces. Do not

texture radially and are of slightly darker color than rest

use a screwdriver to pry components

of body.

apart. Use a loft hammer and tap

(5) If grooves have a sandpaper like texture

gently to loosen the sections on

and are light gray or silver in color (when dry), oil in the

dowel pins.

system is either dirty or foamy. Check for dirty oil,

clogged filters, and leaks in pump suction line.

(2) Remove screws and separate flange (3)

(6) Check seals (1 and 2) for nicked or frayed

from body (18).

lips or signs of leakage. Replace seals if conditions

(3) Remove seals (1 and 2).

exist.

(4) Remove packing (5) and front O -rings (4)

(7) Inspect gear journals on both shafts for

and O -rings (6).

general condition. Small radial scratches left by particles

(5) Tip pump to front and allow bushings (7)

in the oil are normal. If journal surfaces are blackened

to slide out into hand. If bushings do not slide out, jar

and can be easily scratched, they have lost their

them loose by tapping side of pump body with a soft

hardening, and gear assemblies must be replaced.

hammer.

Polish journals with 400 grit sandpaper or finer.

NOTE

(8) Measure gear assemblies for following

Identify bushings as "front" to insure

dimensions: (a)

Journal

diameter-0.872 inch

proper assembly. Interchanging front

minimum.

and rear bushings will greatly reduce

(b) Gear length-1.319 inch minimum.

pump efficiency.

minimum.

(6) Tip pump body to rear and lift out gears

(9) Inspect gears for burs which could cut

(25 and 26).

faces of bushings. Remove burs with fine hone.

(7) Remove bushings (24) in same manner as

(10) Inspect bushings (7 and 24) for dents,

bushing (7) (5 above). Remove rear packings and rings.

deformations, and for grooves cut in faces by foreign

(8) Normally, plug (23) will be forced out by

particles.

spring (20) when flange (3) is removed. If not, turn a 1/4

(11) Hone front and rear faces of bushings with

inch screw into plug and pull out the plug.

an extra fine stone, moving stone in circular motion.

Then remove spool (21) and spring (20).

4-1