GMC PD-4103 Maintenance Manual page 119

GM COACH MAINTENANCE MANUAL
Seco 7
Page 111
ADJUSTMENTS
Refer to "Specifications" at end of this group
for air gap and point opening dimensions and for
closing amperage. The procedures which follow
apply to both units.
Air Gap (Fig. 10)
Press armature down until points just close,
then measure air gap between armature and center
of core. Adjust air gap, if necessary, by loosen-
ing two screws and moving armature up or down
as required. If necessary, align the support carry-
ing the lower contacts so the air gap will be uni-
form between armature and entire top of core.
Point Opening (Fig. 10)
Measure contact point opening with armature
up against stop. Adjust point opening by bending
armature stop. Make sure opening at both points
is equal and that both points close simultaneously
when armature is depressed.
Closing Current (Fig. 10)
Connect an accurate ammeter and a variable
resistance in series at the No. 4 terminal. Close
stop light switch, then reduce resistance until
points close and note ammeter reading when points
close. Increase resistance until points open and
note ammeter reading. If closing and opening
amperage is not within limits listed in "Specifi-
cations," adjust by bending armature spring post
to increase or decrease armature spring tension.
Increasing tension increases closing amperage,
and decreasing tension decreases amperage. Re-
peat this procedure with test equipment connected
to No. 5 terminal to check other unit.
If
relay does not function properly during nor-
mal operation in vehicle, candlepower of stop light
bulbs should be checked. Stop light bulbs of prop-
er size must be used or tell-tale light circuit will
not function.
Circuit Continuity
Connect one prod of test lamp to No. 1 termi-
nal and connect other prod to ground. With brakes
applied (stop light switch closed), manually close
both sets of relay points. If test lamp fails to
light, relay circuit is open. Location of open cir-
cuit is located as follows.
Open Circuit
Connect one prod of test lamp to No. 5 termi-
nal and other prod to ground.
If
test lamp fails
to light when brakes are applied, relay coil is
open circuited. Repeat procedure at No. 4 termi-
nal to test other coil.
MO TO-GARD RELAY
Moto-Gard relay (fig. 11) is used in conjunc-
tion with Moto-Gard and air-operated injector
shut-off system on some vehicles. Relay is mount-
WIRING AND MISC. ELEC.
ed on engine compartment control panel.
Relay points, which are normally closed, are
connected in series with Diesel control switch and
injector shut-off magnet valve. Relay coil winding
is connected in series with the Moto-Gard unit
contacts which are normally open. Refer to "Air
Injector Shut-off and Moto-Gard Wiring Diagram"
in back of manual. Operation of Moto-Gard sys-
tem is previously explained under "Tell-tale Alarm
System."
ADJUSTMENTS
Refer to "Specifications" at end of this group
for air gap and point opening dimensions and for
point opening voltage.
Air Gap (Fig. 11)
Depress armature against stop and measure
air gap between armature and center of core. Ad-
just air gap, if necessary, by loosening two screws
and moving armature up or down as required.
If
necessary, bend lower armature stop to obtain
uniform gap between armature and core.
Point Opening (Fig. 11)
Measure point opening with armature depressed
against lower stop. Adjust point opening, if nec-
essary, by bending upper contact point support.
Opening Voltage (Fig. 11)
Connect an accurate reading voltmeter from
"S" terminal to ground, and connect a variable
resistance in series at the "S" terminal. Place
engine control switch in "RUN" position, but do
not start engine. Wait until low oil condition, due
to engine not running, causes Moto-Gard points to
close, then adjust resistance and note voltmeter
reading at which relay points open and close.
If
not within limits listed in "Specifications," adjust
by bending armature spring stop to increase or
decrease armature spring tension. Increasing ten-
sion increases opening voltage, and decreasing
tension decreases opening voltage.
BEND TO ADJUST
POINT OPENING
Figure 11-Moto-Gard Relay
TP 1594