https://www.truck-manuals.net/mack/ OPERATION 163 MACK TM308M Shifting Instructions
CAUTION Make sure air pressure is at least 90 psi and unit is warmed before shifting the transmission. Use of the clutch brake is for shifting into first and reverse gears only. Do not use the clutch brake to shift out of gear. Be careful not to overspeed the engine during downshifting. Damage to powertrain components can result.
The TM308M is a non-synchronized transmission having a total of eight speeds (6+2) with a non-synchronized air shifted compound section. This LO and HI auxiliary compound section is controlled by an air-shift range selector valve located on the shift lever. The LO range has two low gear ratios. In HI range there are six forward gears which can be shifted in the normal manner, but remember to double-clutch whether moving up or down through the gears. For normal highway use, start in HI range, first gear and shift through second, third, fourth, fifth and sixth. The ratio step between fifth and sixth is smaller than all the other ratio steps. The two gears in LO range are designed for off-highway use and in slow-moving operations (curb pouring, material spreading, heavy load, steep grade). Reverse is used in LO range only. To avoid transmission damage when shifting Forward to Reverse or Reverse to Forward: • Bring vehicle to a stop. • Move lever to NEUTRAL. • Select low range. • Select F or R as desired. • Select lowest lever gear position. • Release and depress clutch pedal. • Select desired gear.
CAUTION Vehicle operators must use extreme caution if operating a truck in the higher reverse gears. Higher reverse gears will produce high reverse speeds which may be difficult for drivers to control dependent on terrain or obstacles.
