TRUCK SERVICE MANUAL
TRANSMISSION
PREVENTIVE MAINTENANCE
Para 3-11
observing performance. Other shops may have test
stands on which the valve body and governor can be
on the transmission for proper travel, routing and
calibrated before installation into the transmission. If test
operation.
stand equipment is not available, satisfactory calibrations
(6) Check the shift selector linkage for proper range
of shift points may be made after road testing of the
selection.
vehicle.
(7) Provide accurate instrumentation required for
observing speeds, temperatures, pressures, etc.
b. Location of Adjusting Components
d. Calibration by Road Test Method
NOTE
(1) Shift speeds are changed by changing the
Before road test, determine the vehicle tachometer error
positions of adjusting rings that determine the retaining
with a test tachometer. Make corrections for error, as
force of certain valve springs in the valve body. Refer to
required, in subsequent tests.
items 80, 85, 81 and 22 (B, foldout 16) and 15 (A, foldout
17).
(1) Check the no-load governed speed of the
engine. Adjust the governor, if necessary, to meet the no-
(2) A special tool J24314 (item 45, fig. 4-3) is used
load governed speed specified for your particular engine-
to depress and rotate the adjusting rings to the proper
transmission
match
(available
from
vehicle
positions. Clockwise rotation increases spring force and
manufacturer).
will raise the shift point. Counterclockwise rotation will
reduce spring force, and lower the shift point.
(2) Note the engine speed and record it. Subtract
100 rpm, and record the remainder as the desired speed
NOTE
for all automatic upshifts except the 1-2 shift This shift
Each notch of adjustment will alter the shift point as
must occur at 100 rpm below lockup engagement speed.
follows.
(3) If doubt exists regarding when lockup is
HT 750CRD
Shift 1-2 - 10 rpm
occurring , install a 0-300 psi (0-2068 kPa) gage at the
Shift 2-3 - 10 rpm
lockup pressure tap. Duringroad operation in 1-hold
Shift 3-4 - 25 rpm
observe the first movement of the gage and note rpm.
Shift 4-5 - 35 rpm
This is first gear lockup engagement speed.
c. Checks Before Adjusting Shift Points
(4) While driving the vehicle in 2-5 range, check the
(1) When calibration is to be made during a road
wide open throttle upshift points. These shifts should
test, or on a test stand that simulates road operation,
occur at 100 rpm below engine no-load governed speed.
certain preparations must be made.
If upshift speed points do not reach those specified, the
(2) Raise the temperature of the transmission fluid in
shiftpoint speed may be raised by adjusting (increasing)
the transmission or test stand to (160 to 220F [71 to
the spring load on the 1-2, 2-3, 3-4 or 4-5 shift signal
1040C]).
valve. If upshift speeds are above those engine speeds
(3) Check the engine no-load governor setting, and
specified, or do not occur at all, the spring load(s)
adjust if required, to conform to the transmission's engine
must be reduced. Only the load on springs for the valve
speed requirements.
(or valves) which do not upshift at the proper speed
(4) Check the engine for satisfactory performance
require adjustment.
before making shift point adjustments.
(5) Check the throttle linkage that controls the
mechanical modulator valve actuator
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