Chevrolet 70 Series 1970 Service Manual page 215

REAR SUSPENSION 4-2
Figure 1—Two-Speed Axle Electric Shift Controls
position the axle is ready to snap into high speed
ratio a s soon a s the load on the axle g ea rs is
reliev ed .
The torsion spring i s assem b led in the unit so
that it is under approxim ately 50 to 90 pounds
p r e ssu r e , depending upon the s iz e of the axle.
When the spring winding le v e r is moved so that
the spring is wound, the p ressu re of the spring is
ra ise d to approxim ately 90 to 140 pounds, de­
pending upon siz e of axle.
The additional p r e ssu r e is used to shift the
a xle. When the shift is com pleted, the ends of the
spring com e together leaving the original tension
Figure 2—Two-Speed Electric Shift Unit Installed
IEaton Axle Shown)
Figure 3 —Position of Drive Screw in High and Low Range
on the spring. Thus p re-load tension holds the axle
in either se lec te d gear.
When the shift button is in LOW range, the
m otor is en ergized so that the m otor arm ature
and drive scr ew rotate to drive nut in opposite
direction for shift into LOW range, in the sam e
manner as p reviou sly d escribed for HIGH range
operation.
SPEEDOMETER ADAPTER
The speedom eter adapter is mounted to back
of speedom eter and i s e le c tr ica lly connected to
control sw itch. When the control sw itch button is
placed in LOW range, an electro-m agn et sh ifts the
adapter m echanism to com pensate for the dif­
feren ce in gear reduction between HIGH and LOW
range in the axle. When shift button is in HIGH
range, current is relea se d
magnet, and a spring holds the adapter m echanism
in HIGH range position.
Speedom eter adapters used on th ese v eh ic le s
are 12 volt type. Voltage of the unit i s stam ped on
the housing below the w ire term inal. Care should
be used to se le c t unit of sam e voltage as v eh icle.
WIRING SYSTEM
R eference should be made to optional equip­
ment wiring diagram s in applicable
D iagram " booklet. The ignition sw itch m ust be on
before e le c tr ic shift m echanism
A separate circuit breaker in the circu it pro­
te c ts the shift circu it in the event of a short.
R efer to "W iring D iagram " booklet for circu it
breaker connections.
INTER-AXLE DIFFERENTIAL
CONTROLS
A differential lock is in stalled a s a part of
forward axle to lock the in ter -a x le differen tial in
the event a wheel or w h eels on one of the driving
a x le s are slipping. Lock is shifted by a power
shift sy stem , controlled by a control le v e r on
instrum ent panel in cab (fig. 4).
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL
from the e lec tro ­
"W iring
w ill operate.