https://www.truck-manuals.net/mack/ OPERATION 169 MACK T309, T309L and T309LR Shifting Instructions
CAUTION Make sure air pressure is at least 90 psi and unit is at operating temperature before making range shifts. Always start in LO range. This also applies to dynamometer testing. When the truck is stationary, do NOT shift into HI range and then start moving the truck. Otherwise, damage to the synchronizer may result.
The T309 unit is a range-shifted transmission which has eight forward highway speeds plus an extra LO speed gear in the LO range. This transmission features a LO and HI auxiliary compound section controlled by an air-shift range selector located on the shift lever. The compound section is equipped with a synchronizer to facilitate LO-HI range shifting. The LO range provides five low ratios. Never attempt to move the vehicle from a stopped position in any gear higher than second gear. Depending on the load, grade or road conditions, it may be necessary to start in LO speed gear or first-second gears. Note that LO speed gear was designed for off-highway use such as paving, material spreading or heavy load/steep grade conditions. The HI range has four forward gears that can be shifted in the standard manner. Remember, however, to double-clutch when moving up or down through these gears. REVERSE can be used in LO range only. Upshift — Under normal highway conditions, with shift lever in NEUTRAL, flip air-shift range selector to LO range, then shift the transmission into first gear (see shift pattern). Shift through second, third and fourth, double-clutching between gears. When maximum RPM is reached in fourth gear, flip air-shift range selector to HI range (preselect) and then move shift lever through NEUTRAL to fifth gear. As the shift lever passes through NEUTRAL, it will put the transmission in HI range. Now continue double-clutching through sixth, seventh and eighth gears.
CAUTION Do NOT move the air-shift range selector while moving in REVERSE. Also, when the truck is stationary, do NOT shift into HI range and then start moving the truck. Damage to the synchronizer may result.
