Manual transmissions are identified by the number of forward gears and the measured distance between the centerline of the output shaft and the counter gear.
The 6-speed manual transmission (RPO MM6/M12) incorporates the following features:
| • | An aluminum case |
| • | Fully synchronized gearing with an enhanced synchronizer cone arrangement: |
| - | Triple-cone: FIRST, SECOND |
| - | Double-cone: THIRD, FOURTH, FIFTH, SIXTH |
| - | Single-cone: REVERSE |
| • | An internal shift rail mechanism |
| • | A remote transmission shift control mounted forward of the transmission |
| • | An external transmission shift rod enabling the forward mount location of the transmission shift control |
| • | An extended-length transmission output shaft mating directly to the rear axle drive pinion, in the rear of the differential housing |
| • | Tapered roller bearings supporting the mainshaft and countershaft |
| • | Caged roller bearings under all speed gears |
| • | Solenoid inhibit of SECOND and THIRD gears |
| • | Solenoid inhibit of REVERSE gear during predefined forward motion |
These features combine to yield a rugged, reliable system capable of handling input torques of up to 610 N·m (450 lb ft) for the MM6 and 540 N·m (400 lb ft) for the M12.
The gear ratios are as follows:
Gear | MM6 Ratio (:1) | M12 Ratio (:1) |
|---|---|---|
FIRST | 2.66 | 2.97 |
SECOND | 1.78 | 2.07 |
THIRD | 1.30 | 1.43 |
FOURTH | 1.00 | 1.00 |
FIFTH | 0.74 | 0.84 |
SIXTH | 0.50 | 0.57 |
REVERSE | 2.90 | 3.28 |
Shift Control and Shift Rod
To allow the rear-of-vehicle transmission location, the transmission shift shaft has been relocated to the front of the transmission. The shift shaft is connected to a transmission shift rod (2) which contains two sealed universal-style joints, enabling the range of motion necessary in order to shift gears. The shift rod (2) is connected to the transmission shift control (1) which is a lubricated and sealed unit, mounted to the driveline support assembly. The mounting system utilized for the shift control (1) incorporates rubber insulators. The cockpit of the vehicle is isolated from the driveline through the use of a shift control closeout boot which seals off the shift control and the driveline tunnel shift control opening.
Gear Select - Skip Shift
To ensure good fuel economy and compliance with federal fuel economy standards, SECOND and THIRD gears are inhibited when shifting out of FIRST gear under the following conditions:
| • | Coolant temperature is above 76°C (169°F). |
| • | Vehicle speed is 24-31 km/h (15-19 mph). |
| • | Throttle is opened 21 percent or less. |
Reverse Lockout
A reverse lockout system, consisting of a reverse lockout solenoid which operates a reverse lockout mechanism, is utilized to prevent shifting into REVERSE gear when the vehicle is moving forward at a speed of 5 km/h (3 mph) or more.
