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Adjust the mechanical modulator per the following procedure:
1. With the modulator cable disconnected at the engine, rotate fuel control lever on the engine to full
throttle position.
2. Adjust modulator slip joint to push cable until the cable comes within 1/8 inch of bottoming, when
throttle is wide open.
3. Adjust the clevis or trunnion on the end of the cable to permit “free pin” with the fuel control lever.
Install and secure the pin.
4. Check accelerator linkage for the proper return to the idle position.
5. Check to be certain there is between 1 3/16" and 1 9/16" travel in modulator cable.
6. If the throttle linkage is readjusted for any reason, the mechanical modulator must be readjusted as
above.
ALLISON AUTOMATIC TRANSMISSION DRIVING TIPS
ACCELERATOR CONTROL
The pressure of your foot on the accelerator pedal influences the automatic shifting. When the pedal is
fully depressed against the pedal stop on the floor, the transmission will automatically upshift near the rec-
ommended governed speed for the engine. A partially depressed position of the pedal will cause the upshifts
to occur sooner at a lesser engine speed. With AT 545 & MT 643 the timing of the shifts is accomplished by
using a cam and cable from the throttle. This provides the accurate shift spacing and control necessary for
maximum performance.
DOWNSHIFT CONTROL AT 545 & MT 643
The transmission can be downshifted or upshifted, even at full throttle, and although there is no speed
limitation on upshifting, there is on downshifting and reverse. Good driving practices indicate that down-
shifting should be avoided when the vehicle is above the maximum speed attainable in the next lower gear.
Therefore, good driving habits have been designed into the Allison transmission shift pattern. The downshift
inhibitors within the valve body prevent those harmful shifts when the vehicle is going too fast for the next
lower gear.
If the downshifts are attempted at excessive speeds, the inhibitors prevent the selected downshift until
the vehicle reaches an acceptable speed.
USING THE ENGINE TO SLOW THE VEHICLE
AT 545 & MT 643
To use the engine as a braking force, shift the range selector to the next lower range. If the vehicle is
exceeding the maximum speed for a lower gear, use the service brakes to slow the vehicle to an acceptable
speed where the transmission may be downshifted safely.
An automatic, compared to a manual, shift transmission has a longer “coast down” time. Until you are
accustomed to this characteristic, you may need to manually downshift to reduce speed.
With a little experience in driving the automatic, you will learn to decelerate a bit sooner, or brake until
automatic downshifts occur. This will reduce the need for manual downshifting.
TRANSMISSION OIL TEMPERATURE
The transmission oil temperature is indicated in some vehicles by a gauge specifically designed for this
purpose and in some vehicles by the engine coolant temperature indicator. Extended operations at low ve-
hicle speeds with the engine at full throttle can cause excessively high oil temperatures in the transmission.
These temperatures may tend to overheat the engine cooling system as well as cause possible transmission
damage.
If excessive temperature is indicated by the engine coolant temperature gauge. Stop the vehicle and
check the cooling system. If the cooling system appears to be functioning properly, shift to neutral and accel-
erate the engine to 1200-1500 RPM. This should reduce the sump temperature to operating level within two
or three minutes. If high temperature persists, stop the engine and have the overheating condition investi-
gated by service personnel.
