Main Control Valve Body Assembly

TM 9-2520-249-34&P

the gear ratio step from fourth gear to third is much

Valve (22)moves against spring (23) when lockup shift

greater than from third to second gears.

valve (43) is against stop (49). Valve (22) limits lockup

d. Manual Selector Valve Operation (FO-12).

pressure to approximately 165 psi.

(2) Included in body assembly (20) is the

(1) Selector valve (9) is actuated by

converter pressure relief valve group (items 26 through

external linkage connected to the operator's manual

29).

These parts limit converter-in pressure to

shift control.

The valve has two parallel internal

approximately 120 psi.

passages--one passage is pressurized at all times and

the other is open to exhaust at all times. Slots, milled

into these passages, are spaced so that each valve

2-22.

Main Control Valve Body Assembly

movement will aline the slots with different ports in

a. General Description (FO-12). Main control

selector valve body (42) Thus, the proper pressure and

valve body assembly (7) works in conjunction with oil

exhaust ports are alined for each of the six driving

transfer plate assembly (15, FO-13), which is bolted to

ranges and neutral.

housing cover assembly (36). The control valve body

(2) Although reverse range, steer, and

contains throttle valve assembly (30, FO-12) and throttle

output clutches are not directly charged or exhausted by

valve regulator assembly (28) in a common bore, the

movements of the selector valve, the pressure (or

downshift inhibitor (items 16 through 24), and selector

absence of pressure) in signal lines connected to the

valve (9). The control valve body also contains throttle

valve does control the charging or exhausting of the

valve lever assembly (34) to which the external throttle

clutches.

linkage is attached.

b. Throttle Valve Operation (FO-12).

2-23.

Steer Valve Body Assembly

(1) Throttle valve assembly (30) is

a. General Description (FO-12). Steer valve

actuated by lever assembly (34) which is linked to the

assembly (54) is attached to separating plate (130)

vehicle throttle. The throttle valve acts against a spring

which is bolted to housing assembly (36, FO-13). The

(29) which acts against throttle regulator valve assembly

steer valve body assembly consists mainly of five

(28) which, in turn, acts against another spring (27).

valves-two identical steer valves (86 and 102, FO-12),

Sufficient movement of the throttle overcomes both

drive relay valve (116), steer relay valve (75), and pivot

spring forces and allows main pressure to assist spring

valve (63). When the output, steer, or reverse clutches

(27) to overcome pressure exerted by spring (29). Thus,

are used as driving clutches, interaction between the

movement of the throttle is proportional to the oil

five valves selects and controls the proper clutch.

pressure assist given to spring (27), which results in

b. Steer Valves Operation (FO-12).

regulated throttle pressure.

(2) At approximately three-quarter open

(1) When steer valves (86 and 102) are in

throttle, throttle pressure comes from the regulator

the "no steer" position, main pressure is blocked at steer

valve. Above this setting, pressure comes directly from

regulator valves (82 and 107).

However, other

the throttle valve. Pressure from the throttle valve is

passages within the valve body allow main pressure to

directed to the lockup shift valve (paragraph 2-21c).

charge the drive clutches during straight travel in any

Thus, above, approximately three-quarter throttle

gear.

opening, engagement of the lockup clutch is delayed;

(2) When steering, one steer valve moves

below this setting, pitot pressure alone controls

in the direction opposite the other steer valve. Thus,

engagement of the lockup clutch. Throttle pressure will

forward movement of one valve interrupts pressure to a

also help to downshift the lockshift valve at heavy

driving clutch and allows it to exhaust, and the

throttle.

simultaneous rearward movement of the other valve

c. Downshift Inhibitor Operation (FO-12).

retains the engagement of the driving clutch that it

controls. The degree of steer is proportional to the

Governor plug (downshift inhibitor) valve (21) is

degree the operator moves the steer control.

actuated by pitot pressure. Pitot pressure pushes

c. Pivot Valve Operation (FO-12).

plunger (24) into the path of lugs formed on selector

valve shaft and lever assembly (32). When the plunger

(1) Pivot valve (63), connected to

is extended, it prevents rotation of the lever assembly

external linkage, is manually controlled by the vehicle

toward a lower gear position. In fourth gear, high-range

operator. Rotation of the pivot valve permits selection

clutch pressure from selector valve (9) is directed

of either of two systems of steering. When valve

between signal (compensator) valves (18 and 19), and

position indicator (65) is pointing rearward, normal

causes signal valve (19) to compress spring (20). This

(geared) steer is available. This steering system is

action delays the movement of plunger (24) away from

known as "land" steering.

When the pivot valve

shaft and lever assembly (32). Turbine speed (and pitot

indicator is pointing 35

pressure) must be lower to permit a 4-3 shift than it is

for 3-2 and 2-1 shifts. This delay is necessary because

2-9