TRUCK SERVICE MANUAL
ELECTRICAL
CLUTCH ASSEMBLIES
b. Opens are usually found where the conductors
Four kinds of clutches or motor drives (a heavy
are joined to the commutator. Loose or poor
duty sprag, a Positork drive, an intermediate duty type
connections will cause arcing and burning of the
and a splined drive) may be used on the enclosed shift
commutator. If the bars are not burned too bad,
lever heavy duty motors.
resolder the leads in the riser bars and turn the
commutator down in a lathe. Then under cut the
The intermediate clutch may be either the sprag
insulation between the commutator bars 1/32".
type or the four roll type. All four types are moved into
c. Grounds in the armature can be found using a
mesh with the flywheel ring gear by action of the
test lamp and prods, see Fig. 12 If the lamp
solenoid. The pinion will remain engaged until starting is
lights when one prod is positioned on the
assured and the solenoid is interrupted.
commutator and the other prod on the armature
core or shaft the armature is grounded.
If the commutator is worn, dirty or out-of-round
or the insulation is high, the commutator should
be turned down and under cut.
4. Reassembly is the reverse of the disassembly.
Heavy Duty Sprag Clutch and DR250 Drive
1. Remove the cupped pinion stop and split
washer. When removing the cupped pinion stop
Fig. 12 Testing Armature for Grounds
it will probably be damaged. A new one will be
required at time of reassembly.
3. Field Coils-- Check field coils for grounds and
opens with a test lamp.
2. Remove remaining parts such as pinion washer
or retainer cups and baffle if equipped. The
a. Grounds With the field coil ground
splined drive will have a spring cup (spring inside
disconnected, position one test prod on
cup).
the field frame and the other to the field
connector. If the lamp lights the field coils
3. DO NOT lubricate the sprags on heavy duty
are grounded and must either be replaced
clutches as they are lubricated for life with a
or repaired.
special lubricant.
b. Opens If the test lamp does not light when
4. Reassembly is the reverse of the disassembly.
the prods are connected to the ends of coil
leads, the field coils are open.
REASSEMB LY
The reassembly procedure for the most part is the
A pole shoe spreader and pole shoe screw driver
reverse of the disassembly.
should be used if the field coils are to be removed. Extra
caution should be taken in replacing the field coils to
prevent grounding or shorting when they are tightened in
place. If the pole shoe has a long lip on one side, it
should be assembled in the direction of armature
rotation.
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