Chevrolet 10 1971 Series Chassis Service Manual page 438

ACCESSORIES 15-4
Fig. 5-Servo Mounting
SERVO UNIT
SERVICE
If the Servo Unit is found to be defective, replacement
is required. Note the condition of the hoses and replace
any which are cracked or deteriorated.
ADJUSTMENT
Adjust the cable slack so it is as tight as possible
without holding the throttle open when the carburetor is
set at its lowest idle throttle position.
When adjusting the cable (engine stopped), manually set
the fast idle cam at its lowest step and adjust the cable
with the two locknuts at the Servo end so that it does not
hold the idle screw off the cam.
REGULATOR
M AINTENANCE
A defective Regulator (that is one which is not simply
out-of-adjustment) must be replaced. During replacement,
check the hoses which connect to the Regulator and re­
place any which are cracked or deteriorated.
ADJUSTMENT
One regulator adjustment is possible.
Cruising Speed Zeroing (to remove any difference between
engagement and cruising speed).
No Regulator adjustment should be made,
NOTE:
however, until the following items have been
checked or serviced:
1. Servo Cable properly adjusted.
2. All hoses in good condition, properly attached, not
leaking, not pinched, or kinked.
3. Electric and vacuum release switches properly
adjusted.
EN G A G E M EN T -C R U ISIN G SPEED ZEROING
If the car cruises at a speed above or below the engage­
ment speed, this error can be corrected with a simple
adjustment of the orifice tube in the transducer (see fig. 3).
1. To check cruise speed error, engage Cruise-Master
at 60 mph.
2. If car cruises below engagement speed, screw the
orifice tube outward.
3. If car cruises above engagement speed, screw the
orifice tube inward.
NOTE:
change cruise speed approximately one mph.
Snug-up lock nut after each adjustment before
testing.
CAUTION:
casting.
ELECTRICAL SYSTEM CHECK (Fig. 6)
1. Check fuse and connector.
2. Check electric brake switch as follows:
a. Unplug connector at switch.
b. Connect ohmmeter at points A and B on brake
switch. The ohmmeter must indicate no continuity
when the pedal is depressed and continuity when
pendal is released. The cruise release brake
switch (electric) is adjusted as is the standard
stop light brake switch.
c. Replace electric brake switch if needed.
3. Check clutch release switch (manual trans. only)
same as electric release switch above.
1. Check engagement switch and connecting wiring as
follows: Unplug engagement switch connector (brown,
blue, black) at electrical wiring harness connector
then perform the following tests (fig. 6).
Test #1 - Connect ohmmeter between terminal #1
(brown wire) and terminal #2 (blue wire). Continuity
shall be maintained until switch is depressed all the
way in.
Test #2 - Connect ohmmeter between terminal #1
(brown wire) and terminal #3 (black wire). No con­
tinuity shall be shown; however, when the button is
depressed halfway, continuity shall be indicated.
When the button is pressed all the way down, no
continuity shall be shown.
Test #3 - Connect ohmmeter between terminal #2
(blue wire) and terminal #3 (black wire). Button
released, no continuity; however, when the button is
depressed partially and fully, continuity shall be
shown.
Engagement
1. Disconnect engage switch wire harness connector
from the main harness connector (red, brown/white,
and white wires).
2. Connect ohmmeter between point C (brown/white
stripe wire in main wire harness) and ground. Make
sure the Regulator is well grounded to the chassis.
The ohmmeter should read between 42 and 49 ohms.
If a resistance either above or below the valve indi­
cated is shown, then disconnect the connector from
the Regulator and measure the resistance of the
Each 1/4 turn of the orifice tube will
Do not remove orifice tube from
ENGAGEMENT SWITCH TEST
HARNESS TEST
10-30 CHEVROLET TRUCK SERVICE MANUAL