GMC T Series 1994 Repair Manual page 590

STARTER MOTOR
The Delco Remy 28-MT is a gear reduction starter.
An internal gear at the gear-reduction end of the
driveshaft is driven by the armature shaft gear at a
speed of one drive shaft revolution for each 3.9 revolu­
tions of the armature.
NO-LOAD TEST
Before disassembling the starter motor for repair, the
following tests should be made.
N O T IC E : N e v e r o p e r a t e
m o r e t h a n 3 0 s e c o n d s
p a u s i n g to a l l o w i t to c o o l f o r a t l e a s t 2 m in ­
u t e s . O v e r h e a t i n g ,
c r a n k in g , w ill d a m a g e th e s t a r t e r m o to r .
Inspect
1. Pinion for freedom of rotation by turning it in the
overrun direction on the shaft. The pinion should
rotate without turning the drive assembly shaft.
2. Armature for freedom of rotation by turning the pin­
ion in the cranking direction. The pinion, shaft, and
body of the drive assembly should all rotate togeth­
er. If necessary, pry the pinion with a screwdriver to
turn it.
• Tight bearings, a bent armature shaft, or a
loose pole screw will cause the armature to
bind.
• If the armature does not turn freely, the motor
should be disassembled.
• If the armature rotates freely, the motor should
be given a no-load test before disassembly.
Figure 1—28-MT Starter Motor
GENERAL DESCRIPTION
DIAGNOSIS
t h e s t a r t e r m o t o r
a t a t i m e w it h o u t
c a u s e d b y t o o m u c h
The starter has an overrunning roller-type clutch and
an enclosed shift lever. The solenoid is sealed to pre­
vent entry of foreign material.
IDENTIFICATION
The part number is stamped on a label and attached
to the field frame (figure 1).
Test Connections
Connect the starter motor for the test as shown in
figure 2.
1. Secure the starter motor in a test stand.
2. Use a momentary contact pushbutton switch in the
test circuit that can be released quickly if very high
current surges occur.
3. Make all connections and disconnections with the
switch open and the carbon pile off.
4. If sparking or current flow occurs in the battery
circuit when connections are being made, the start­
er motor solenoid switch contacts may be frozen
shut.
5. As the last step in making test connections, ground
the negative battery cable securely to a clean met­
al ground on the starter motor frame.
6. The carbon pile load is used to adjust operating
voltage for comparison with specifications. It may
not be necessary in all cases.
Test Procedure
CAUTION: Keep fingers and tools away from
the opening in the drive end housing while
testing. The strong shifting action of the sole­
noid could cause personal injury or damage
as the drive pinion moves into the cranking
position and spins.