Section XV. REPAIR OF DIRECTIONAL CONTROL SWITCH

TM 10-3930-609-35

shaft and connect potentiometer leads to terminals

3-103.

Inspecting Disassembled Parts of

board.

Accelerator Controller

a. Inspect all structural parts (brackets, supports,

Note

cover and box assembly) for cracks and deformation.

If potentiometer has three terminals,

b. Using an ohmmeter, check switches for contact

select pair of terminals across which

closure when operated manually.

resistance decreases as shaft is

c. Using an ohmmeter, check potentiometer for

rotated clockwise.

resistance variation of 600,000 to zero ohms when shaft

is rotated through full range.

e. Rotate main shaft fully counterclockwise and

d. Check that resistance between either terminal of

rotate potentiometer shaft fully clockwise as seen from

potentiometer and potentiometer case is one megohm

outer end of potentiometer shaft; then, back off two to

minimum.

three degrees. Mount support on box assembly with

e. Inspect gear sector and pinion for worn or

pinion gear on potentiometer shaft meshed with gear

chipped teeth.

sector on shaft.

f. Inspect bearings in box assembly for excessive

f. Adjust first switch support so that first switch

wear, causing looseness of shaft.

actuates as main shaft is rotated approximately seven

g. Inspect all threaded parts and tapped holes for

degrees clockwise. With first switch just actuated,

stripped threads or other damage.

resistance across potentiometer must be 3,500 to 6,600

ohms. If necessary, readjust timing of potentiometer by

3-104.

Repair and Replacement of Accelerator

loosening shaft clamp and rotating potentiometer shaft

Controller Parts

in pinion. Tighten clamp after adjusting.

a. Repair minor thread damage with tap or thread

chaser.

Note

b. Replace all distorted or worn parts with

Plunger in switches must have 1/32

serviceable parts.

inch

overtravel

after

switch

c. Replace switches or potentiometer if improper

actuation. Adjust switch brackets

operation is detected while checking.

using screw and nut. Ensure that

nut is tight when making final check.

3-105. Reassembly of Accelerator Controller (fig. 3-

g. Adjust second switch to actuate when shaft is

20)

rotated to 27 degree position (corresponding to full

speed of truck). With second switch just actuated,

a. Insert shaft into box assembly bearing and place

resistance across potentiometer must be 200 ohms or

collar, hub and gear sector, cams and stop on shaft

less.

while inserting shaft, using keys in keyways in shaft.

Secure collar, hub and stop to shaft with setscrews and

h. Secure cover on box assembly with screws and

secure cams to shaft with screws and lockwashers.

lockwashers.

Adjust stop screws to limit rotation of shaft to 30

i. Mount box assembly on bracket with screws and

degrees.

lockwashers.

b. Mount switches on switch supports with screws;

j. Mount lever on main shaft with screw, nut and

then, attach switch supports to box assembly with

lockwasher; mount screw and locknut for spring in lever;

screws, nuts and fulcrums.

mount ball joint on lever with screw and lockwasher;

c. Attach terminal board to bracket on support with

and, screw rod into ball joint and lock with nut.

screws.

d. Mount potentiometer on potentiometer bracket

with nut; then, mount pinion and clamp on potentiometer

Section XV. REPAIR OF DIRECTIONAL CONTROL SWITCH

3-106. Description of Directional Control Switch

3-107. Removal of Directional Control Switch

Removal of the directional control switch from the truck

The directional control switch is a lever-operated,

double-pole, double-throw switch with center off

is recommended for repair as described in the following

position. Detents are provided to maintain contacts in

instructions. Refer to paragraph 2-19 for removal

closed position when lever is released. A special trip

procedure.

mechanism returns the switch to the center off position

from either on position when the operator rises from the

seat.

3-37