Allison Transmissions

The Allison 1000 transmission is a first-in-class six-speed automatic for the 2006 Chevrolet Silverado HD and GMC Sierra HD trucks equipped with the Duramax 6600 6.6L V-8 diesel or Vortec 8100 8.1L V-8. Also new for 2006, the Allison 1000 six-speed features a class-first tap-shift range selection function, as well as offering enhanced fuel mileage, quietness and control. The range selection function allows the driver to easily select the desired gears to match driving conditions, such as towing a trailer on a steep grade.

The sixth gear – essentially a second overdrive gear – enables a wide, 5.08:1 overall forward gear ratio coverage and allows the vehicle’s engine to operate at lower rpm, particularly during higher-speed driving on highways and freeways. Its 0.61 ratio sixth gear provides a 1550-rpm engine speed at 60 mph, compared with the five-speed transmission’s 1800-rpm engine speed at 60 mph. The engine uses less fuel at lower rpm, enabling increased fuel mileage and range. The ratios of gears 1 through 5 remain the same as the Allison 1000 five-speed, including the 0.71:1 fifth gear.

A tow/haul mode is retained on the Allison 1000 six-speed, but it is complemented by a new range selection feature. It allows the driver to select the desired gears, via a thumb-activated switch on the shifter, providing a feeling of enhanced control in unique driving situations, such as towing on a steep grade. The range selection feature holds the gear pre-selected by the driver and electronic safeguards prevent the transmission from being shifted in a manner that could cause engine damage or loss of vehicle control. Grade braking and cruise grade braking are only available when the tow/haul mode is selected and the transmission is not in the range selection mode.

Diesel-engine vehicles equipped with the Allison 1000 six-speed feature cruise control grade braking. Working in harmony with the tow/haul mode, the cruise grade braking system will automatically downshift to help maintain the pre-selected cruise speed when driving on downhill grades.

A new low-traction mode also is standard on vehicles equipped with the diesel engine. When the driver selects second gear while stopped and wheel slip occurs, the transmission torque-manages the engine to limit tire slip on slippery road surfaces.

In addition to the sixth gear and range selection feature, the Allison 1000 also benefits from complementary upgrades that include:

* Upgraded 310-mm torque converter that improves torque capacity

* New 22-tooth pump that improves NVH

* New solenoids provide better converter lock-up control and shift feel

* Upgraded rotating clutch that improves torque capacity

* New A40, 32-bit transmission control module

The Allison 1000 also has a unique, GM-patented elevated idle mode, which allows for faster interior warm-up of diesel-equipped vehicles. The system, which is activated through the vehicle’s driver information center, is synchronized with the engine. When elevated idle is active, the transmission increases the load on the engine so that it will generate heat more quickly and warm the interior in less time.