Chevrolet 70 Series 1970, Service Manual

Page: 215 / 841

REAR SUSPENSION 4-2
Figure 1—Two-Speed Axle Electric Shift Controls
p osition the axle is ready to snap into high speed
ratio a s soon a s the load on the axle g e a rs is
reliev ed .
The to rsio n spring i s a ssem b led in the unit so
that it i s under approxim ately 50 to 90 pounds
p r e s s u 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 r e ssu r e of the spring is
r a ise d to approxim ately 90 to 140 pounds, de­
pending upon s iz e of axle.
The additional p r e ssu r e is used to shift the
a x le. When the sh ift is com pleted, the ends of the
sp rin g 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 r e-lo a d ten sion holds the axle
in eith er se le c 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 sc r e w rotate to drive nut in opposite
direction for shift into LOW range, in the sam e
manner a s p rev io u sly d escrib ed for HIGH range
operation.
SPEEDOMETER ADAPTER
The speedom eter adapter is mounted to back
of sp eed om eter and i s e le c tr ic a lly connected to
control sw itch. When the control sw itch button is
placed in LOW range, an electro -m a g n et sh ifts the
adapter m echanism to com pensate for the dif­
feren ce in gear reduction betw een HIGH and LOW
range in the axle. When sh ift button is in HIGH
range, current is r e le a se d from the e le c tr o ­
m agnet, and a spring holds the adapter m echanism
in HIGH range position.
Speedom eter adapters u sed on th ese v e h ic le s
are 12 volt type. V oltage of the unit i s stam ped on
the housing below the w ire term in al. Care should
be used to s e le c t unit of sam e voltage a s v eh icle.
WIRING SYSTEM
R eferen ce should be made to optional equip­
ment wiring diagram s in applicable "W iring
D iagram ” booklet. The ignition sw itch m ust be on
b efore e le c tr ic sh ift m echanism w ill operate.
A sep arate circu it b reaker 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
b reak er connections.
INTER-AXLE DIFFERENTIAL
CONTROLS
A differential lock is in sta lled a s a part of
forw ard axle to lock the in te r -a x le d ifferen tial in
the event a w heel or w h eels on one of the driving
a x le s are slipping. Lock i s shifted by a power
shift sy ste m , 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