WHEEL BRAKES

TM 10-3930-623-12

of the pump valve is also fed from an orifice directly by

(7)

Remove cotter pin (25), nut (26) and

main pressure which positions the pump valve so that oil

washer (27) and pull wheels, brake drum, brake drum

from the inching valve can flow through it to the selector

seal, gasket, and final drive shaft from axle housing as

valve.

an assembly.

4-50. Converter Oil. Converter oil flow c mes directly

(8)

Disassemble hydraulic brake assembly

from the oil pump outlet, but is reduced in pressure in

as follows:

passing through an orifice to get into the converter. Exit

(a)

Press outer of two spring retainers (2)

oil from the converter goes to a bypass valve located in

inward to compress springs (1) and turn it 90 degrees to

the converter oil, out line. This bypass valve directs the

free retainer and spring from spring rod (3). Remove

oil to the sump in case of a clogged oil cooler or clogged

items 1, 2 and 3 from assembly.

cooler lines and provides a safety feature against

(b)

Spread brake shoes (6) apart at top,

extreme internal converter pressures caused by

enough to permit them to be removed from packing plate

accidental restrictions. Oil from the cooler is directed to

(17) with springs still attached. Remove brake shoes

the lubrication circuit which maintains a flow of cooled oil

and springs (4 and 5). Lever (7) will be freed at the

under pressure to the clutch plates and bearings in the

same time.

transmission.

(c)

Remove two brake push rods (8), dust

4-51. WHEEL BRAKES (see figure 4-6). The wheels of

boots (11), pistons (12), cups (13), and spring (14) at

the drive axle are fitted with a set of drum-and-shoe type

each brake. Remove two screws and washers (9 and

brakes. The design and principles of operation of these

10) and take wheel cylinder (15) and spacer (16) from

brakes are simple, and generally similar to the most

backing plate (17). Remove and discard felt seal (18).

commonly used automotive hydraulic brakes. The brake

b. Cleaning and Inspection.

assembly at each wheel consists of the following

(1)

Wipe the brake shoes with a clean dry

principal parts:

cloth. Clean all other parts with dry cleaning solvent

1. Backing plate (7) on which the nonrotating parts of

(Federal Specification P-D-680) and dry thoroughly.

the brake mechanism are mounted. The backing plate is

(2)

Inspect brake lining for graze, grease or oil

anchored to the reduction gear housing, and cannot

soaked condition, and wear. Inspect wheel cylinder bore

rotate.

for rust pits or scoring. Replace cylinders which can not

2. Two lined brake shoes (16) mounted on the

be reconditioned with light honing. Inspect rubber cups

backing plate. The shoes are anchored at one end so

and boots for cracks or deterioration. Replace brake

they can pivot slightly on the anchor point, and are

shoes if lining is glazed, grease or oil soaked, or if lining

separated at the other end by a hydraulic cylinder (15)

thickness is less than 1/8 inch. Replace defective wheel

which spreads them in operation, to press them against

cylinder cups and boots if cylinder can be honed

the brake drum (4).

effectively. If wheel cylinder is badly pitted, replace

3. A hydraulic cylinder (15) (called the wheel cylinder

cylinder assembly.

to distinguish it from the pedal actuated master cylinder)

c. Repair. Repairs consist of replacement of the

is fastened to the backing plate.

brake shoes in matched sets on both wheels and rebuild

or replacement of the wheel cylinder. Rebuild kits are

Removal.

available to replace the internal parts of the wheel

(1)

Block up front of truck so weight is taken

cylinder. Brake shoes are always replaced in full sets to

from front wheels.

maintain equal braking.

(2)

Drain oil from power axle.

(3)

Disconnect brake hoses (2 and 3, fig. 6-6 )

from elbows (4).

(4)

Disconnect parking brake linkage at

parking brake lever(2, fig. 4-6.1).

(5)

Remove cotter pin (3) and nut (4) and

remove parking brake lever (2) from brake lever and pin

assembly (45).

(6)

Remove screws (22) and washers (23)

and separate sections of final drive gear case (47) from

axle housing (61).

4-8