Mack Granite GU Series, Operator'S Handbook Manual

Page: 213 / 317

202 OPERATION
MACK TM309M 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 TM309M is a non-synchronized transmission having a total of nine
speeds (6+3) with an air shifted non-synchronized 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 three 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 three gears in LO range are designed
for off-highway use and in slow-moving operations (curb pouring, material
spreading, heavy load, steep grade). Only start in the lowest gear necessary
to move the vehicle. The extreme LO gear (1st low) is intended for vehicular
speed control and not for torque multiplication.
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.