Chevrolet 1977 light duty truck, Service Manual

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b. Low line pressure.
c. Case valve body face not flat or porosity
between channels.
3. D IR E C T C L U T C H
a. Restricted orifice in vacuum line to m odulator
(poor vacuum response).
b. Check ball in direct clutch piston dam aged,
stuck or missing.
c. Defective m odulator bellows.
d. Clutch piston seals d a m a g e d or missing.
e. Case valve body face not flat or porosity
between channels.
f. Clutch installed backwards.
N O T E : Burned clutch plates can be caused by
incorrect usage o f clutch plates. Also, anti-freeze in
transmission fluid can cause severe dam age, such
as large pieces o f composition clutch plate material
peeling off.
G O VE R N O R PRESSURE CHECK
1. Install line Pressure Gage, to tap location shown
in Fig. 7A-10B.
2.
Disconnect vacuum line to moldulator.
3. With car on hoist (rear wheels, off ground), foot
off brake, in drive, check line pressure at 1000 RPM.
4. Slowly increase engine RPM to 3000 RPM and
d e term in e if a line pressure d rop occurs (7 PS1 or more).
5. If no pressure d rop occurs:
a. Inspect G overnor
1. Stuck valve.
2.
Free Weights.
3. Restricted orifice in governor valve.
b. G o v e rn o r Feed System
1. Check screen in control valve assembly.
2.
Check for restrictions in I'eed line.
3. Scored governor bore.
M A N U A L LINKAG E
M anual linkage adjustm ent and the associated
neutral safety switch are im portant fro m a safety
standpoint. The neutral safety switch should be adjusted
so that the engine will start in the Park and Neutral
positions only.
With the selector lever in the Park position, the
parking pawl should freely engage and prevent the
vehicle from rolling. The pointer on the indicator
q u a d ra n t should line up properly with the range
indicators in all ranges.
ROAD TEST
Drive Range
Position selector lever in DRIVE R A N G E and
accelerate the vehicle from 0 MPH. A 1-2 and 2-3 shift
should occur at all throttle openings. (The shift points
will vary with the throttle opening). As the vehicle
decreases in speed to 0 MPH, the 3-2 and 2-1 shifts
should occur.
Low L2 Range
Position the selector lever in L2 R A N G E and
accelerate the vehicle from 0 M PH. A 1-2 shift should
occur at all throttle openings. (No. 2-3 shift can be
obtained in this range). The 1-2 shift point will vary with
throttle opening. As the vehicle decreases in speed to 0
MPH, a 2-1 shift should occur.
The 1-2 shift in IN T E R M E D IA T E R A N G E is
somewhat firmer than in DRIVE R A N G E . This is
normal.
Low L I Range
Position the selector lever in L I R A N G E and
accelerate the vehicle from 0 MPH. No upshift should
occur in this range.
2 N D Gear — Overrun Braking: (L2)
Position the selector lever in DRIVE R A N G E , and
with the vehicle speed at approximately 35 MPH, move
the selector lever to L2 R A N G E . The transmission
should downshift to 2nd. An increase in engine RPM
and an engine braking effect should be noticed. Line
pressure should change from approxim ately 100 PSI to
approxim ately 125 PSI in 2nd.
1ST Gear — Overrun Braking: ( L I )
Position the selector lever in L2 R A N G E at
approxim ately 30 to 50 MPH, with throttle closed, move
the selector lever to LI. A 2-1 downshift should occur in
the speed range o f approxim ately 45 to 30 MPH,
depending on axle ratio and valve body calibration. The
2-1 downshift at closed throttle will be accom panied by
increased engine RPM and an engine braking effect