Chevrolet 10 Series 1970 Service Manual page 211

F ig . 6 2 — E le c tric S h ift C o n tro l S w itch
When the nut has tra ve led fa r enough to wind the
sprin g, a contact bumper on the nut breaks an e le c tric a l
connection on the automatic switch which d e -e n e rg iz e s
the m otor and stops arm ature rotation. The nut is held
at the end o f its tra v e l on the screw by a detent spring on
the shifting housing front cover.
A s the nut m oves downward, the spring winding le v e r ,
which pivots on a pin in the nut, winds the torsion spring.
Thus the tension o f the spring is increased, and in this
position, the axle is ready to shift into the high speed
ra tio as soon as the load on the axle g ea rs is re lie v e d .
The torsion spring is assem bled in the unit so that it is
under 65 pounds p ressu re. When the spring is wound by
the winding le v e r , this tension is in creased to 115 pounds.
Th is additional p ressu re is used to shift the axle. When
F ig . 6 3 — E le c tric S h ift U n it M o unte d
REAR SUSPENSION AND DRIVE LINE 4-35
F ig . 6 4 —S h ift U n it in H igh Range P osition
the shift is com pleted, the ends o f the spring come to ­
geth er, leaving the orig in a l tension in the spring. This
prelo ad tension holds the axle in either range.
Low Speed Range
When the control switch operating arm is m oved to the
down (LO ) position, cu rrent is supplied to the other field
o f the m otor and to the speedom eter adapter. The cu r­
rent now causes the arm ature and screw to turn counter­
clockw ise, and the nut tra v e ls toward the top o f the screw
(fig . 65). Th is winds the torsion spring fo r a shift to low
range which is accom plished in the same manner as the
shift to high range.
General M aintenance
The only gen eral maintenance n ecessary on the shift
control system is to make sure that a ll w irin g is in good
F ig . 6 5 —S h ift U n it in Low Range P osition
CHEVROLET TRUCK SERVICE MANUAL