Chevrolet 70 1969 Series, Shop Manual

Page: 143 / 913

REAR SUSPENSION 4 A -4
BENT HOUSING CHECK
A check for bent axle housing can be made
with unit in vehicle in following manner; however,
conventional alignment instruments can be used if
available.
1. Raise rear axle with a jack until wheels
clear floor. Block up axle under each spring seat.
2. Check wheel bearing adjustment and adjust
if necessary, then check wheels for looseness and
tighten wheel nuts if necessary. Refer to "R E A R
HUBS A N D B E A R IN G S'(SE C . 4C).
3. Place a chalk mark on outer side wall of
tires at bottom. Measure across tires at chalk
marks with a toe-in gauge.
4. Turn wheels half-way around so that chalk
marks are positioned at top of wheel. Measure
across tires again. If measurement at top is 1 /8 "
or more smaller than previous measurement noted
at bottom of wheels, axle housing has sagged and
is bent. If measurement at top exceeds bottom
dimension by 1/ 8 " or more, axle housing is bent
at ends.
5. Turn chalk marks on both wheels so that
marks are level with axle and toward rear of ve­
hicle. Take measurement with toe-in gauge at chalk
marks; then turn both chalk marks to front and
level with axle and take another measurement. If
measurement at front exceeds rear dimension by
1 /8 " or more, axle is bent to the rear. If the
measurement condition is the reverse, the axle
is bent forward.
ELECTRIC SHIFT MAINTENANCE
A N D DIAGNOSIS
The only general maintenance necessary on the
shift control system is periodic lubrication of unit
as described in LU B R IC A T ION (SEC. 0). The wir­
ing connectors should be kept tight, and wires to
the various units should be kept in good condition.
D IAGN OSING T R O U B L E
If the electric shift fails to operate properly,
the system should be tested and the trouble diag­
nosed as described in following paragraphs. A test
light consisting of a 12-volt bulb with two wires a
few feet long with small battery clips on the ends.
Refer to wiring diagram and test in following se­
quence:
1. Disconnect two wires from shift unit at
rear axle. Place engine control or ignition switch
in " O N " position, also place axle shift switch at
shift lever in "H I" position.
2. Connect one lead of test light to ribbed wire
and opposite lead to ground. One of the following
conditions should exist:
a. Should light come oh and stay on, the cir­
cuit is satisfactory and any trouble will probably
be found in the shift unit. Repeat check for " L O "
position as directed in step 3 following.
b. If the light fails to come on, this indicates
that the circuit is open between the control switch
and the shift unit and further tests will be required.
c. If the light comes on but cycles, this indi­
cates that there is a short between the control or
ignition switch and shift unit, and further tests
will be required.
3. Remove test light lead from ribbed wire
and connect to smooth wire, also place axle shift
switch in " L O " position. Observe conditions as
outlined in sub-paragraphs above.
4. Connect one lead of test light to control
switch side of circuit breaker and opposite lead to
ground. Should light come on, and stay on, the cir­
cuit is satisfactory. However, if the light fails to
come on the circuit between the control switch and
circuit breaker is either open or shorted.
5. Connect one test lead to load side of circuit
breaker and opposite lead to ground. Should light
come on, and stay on, the circuit breaker is satis­
factory. However, if the light fails to come on the
circuit breaker is faulty.
6. At chassis junction, remove both wires,
then test circuit through red wire with white stripe.
Reconnect both wires to terminal.
7. At chassis junction, remove wire from
terminal. Place axle shift lever switch in " L O "
position and test circuit.
8. At chassis junction, remove wire from
terminal. Place axle shift lever switch in "H I"
position and test circuit.
The preceding tests should readily localize
any trouble within the system. When checking the
wiring harness for shorts or open circuits, exam­
ine for broken insulation.
The control or ignition switch can be best test­
ed by substituting a new unit.
If the vehicle shifts normally, but the speed­
ometer adapter fails to operate, make the test to
determine whether the adapter is getting current
in low range. If current is present, replace the
adapter. When the trouble is traced to the shift
unit, it should be replaced.
INTER-AXLE DIFFERENTIAL
CONTROL LEAKAGE TEST
AIR L E A K A G E T E S T
1. Build up air pressure in air system to m ax­
imum pressure limit (100 to 105 lbs.). Place axle
shift control lever in " L O C K " position.
2. Coat all air line connections with soap suds
to check for leakage. No leakage in air line con­
nections is permissible. Leakage can sometimes
be corrected by tightening the connection.
3. If this fails to correct leakage, remove line
having leaking connection. Slide tube nut back on
CHEVROLET SERIES 70-80 H EAVY DUTY TRUCK S H O P M A N U A L