Chevrolet 10 Series 1968, Руководство по обслуживанию

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CLUTCHES AND TRANSMISSIONS 7-23
a. Turning screw in (clockwise) raises air pressure.
b. Turning screw out lowers air pressure.
Check Point “ B”
1. Pull the control button up to high range and discon­
nect the black 1 / 8 " nylon air line from “ out” port
of control valve at the air valve.
2. When control button is pushed down a steady blast of
air will flow from the control valve (port where black
line was disconnected). A ir will shut off when button
is pulled up. This indicates that control valve is op­
erating correctly. Reconnect air line.
3. If control valve does not operate correctly, check for
restrictions or leaks. Leaks indicate defective “ O”
rings in the control valve.
Check Point “ C ”
1. Push the control button down to the low range posi­
tion, then disconnect the high range air line, either
at fitting on shift cylinder or at side port of air
valve.
2. Pull the control button up. There should be a steady
flow of air from the high range port on the air valve.
Push button down to shut off air.
3. With vehicle engine not running, move the gearshift
lever to any gear position. Pull the control button
up; there should be no air at the high range port.
Move the gearshift to neutral; there should now be a
steady flow of air from the high range port. Push
control button down to shut off air and reconnect
the high range air line.
4. If the air system operates incorrectly, this indicates
that the air valve is defective, or that actuating parts
in shifting bar housing are jammed or defective.
Check Point “ D”
1. Pull the control button up to high range and discon­
nect the low range air line, either at fitting on the
shift cylinder or at side port of air valve.
2. Repeat procedures under Check Point
“ C , ”
revers­
ing the position of the control button in order to
check low range operation.
Check Point “ E” (Refer to Fig. 11C)
If any of the seals in the range shift cylinder are de­
fective, the range shift will be affected. The degree of
lost air will govern the degree of failure, from slow shift
to complete failure.
1. Leakage at seal
“ A ”
or “ B” results in failure to
shift into either low or high range; steady leak out
air valve breather in both ranges.
2. Leakage at seal
“ C ”
results in failure to shift into
low range; pressurizing of transmission.
TRANSMISSION OVERDRIVE
INDEX
Page
General D e s c r ip t io n ............................................................. ... 7-23
Maintenance and A d ju s tm e n ts ................................................ 7-24
Governor Switch and P in io n ................................................ 7-24
Sun Gear Solenoid, Oil Seal & Control Cable Bracket . . 7-24
Case R ear Oil S e a ls ..........................................................
7-24
Control Shaft L e v er and/or “ O” Ring O i l ................... ...7-24
Speedometer Driven G e a r ................................................ ...7-24
E le ctric a l Unit Checks ................................................... ... 7-24
O verd rive R e l a y ............................................................. ... 7-24
A ir G a p .......................................................................... 7-24
Point O p e n in g ............................................................. 7-24
Page
Closing V o l t a g e ............................................................. ... 7-24
Solenoid ............................................................................. ... 7-25
Closing C o i l ................................................................... ... 7-25
Engaging S p r in g ............................................................. ... 7-25
Ignition Grounding C o n t a c t ............................................. 7-25
Governor S w itc h ................................................................ ... 7-25
Kickdown S w it c h ................................................................ ... 7-25
Linkage Adjustment................................................................ ... 7-25
Diagnosis - O v e r d r iv e ................................................................ 7-26
M e c h a n ic a l............................................................................. ... 7-26
E lectrica l
............................................................................. ... 7-27
GENERAL DESCRIPTION
The overdrive unit is essentially a two-speed planetary
transmission attached to the rear of a fully synchronized
three-speed transmission. In overdrive, engine speed is
approximately 30 per cent slower at a given road speed
since the drive train includes planetary gears which pro­
vide a lower overall gear ratio than that obtained in high
gear with the conventional transmission.
The electrical equipment which controls the automatic
action of the mechanical portion of the overdrive unit
consists of a solenoid, a speed-sensitive governor switch,
a relay and kickdown switch. The circuit including this
equipment makes it possible to operate in overdrive
above a pre-set cut-in speed, or in conventional drive at
any speed.
SERVICING THE OVERDRIVE
Repairs to the overdrive housing, output shaft, ring
gear assembly, clutch cam, roller retainer, pinion cage,
sun gear, shift rail, sun gear control plate, output shaft
bearing, oil seal, speedometer drive gear, solenoid pawl
and interlock plunger may be performed underneath the
vehicle, if so desired, by removing the overdrive housing
without disturbing the transmission. Refer to the Truck
Overhaul Manual for Service Procedure.
If the transmission mainshaft, overdrive adapter or
transmission rear bearing which is retained in adapter
require replacement, the entire transmission and over­
drive assembly should be removed and overhauled on the
bench,
CHEVROLET TRUCK SERVICE MANUAL