Adaptive Hill Hold
Don't you hate it when you're stopped on a hill while towing a load and your truck starts to roll backward when you take your foot off the brake, even though you've got the automatic transmission in Drive? GM says it's studying two different "Adaptive Hill Hold" systems to prevent this. The first engages a third clutching element in the transmission to hold the transmission-output shaft from turning; a second system senses vehicle roll and modulates the throttle to increase torque output of the powertrain to hold the vehicle stationary. Both systems enhance safety and driver comfort behind the wheel, especially when towing a trailer. All automatic-transmission-equipped vehicles are candidates for Hill Hold, but GM says it has no firm production plans for the systems yet.--C.S.
Six-Speed Automatic Transmission
One of the biggest complaints from those who tow or haul heavy loads with pickups and SUV is the loss of engine rpm and resulting loss of momentum during gear changes. More gears with ratios spaced closer together is the solution. But while GM has some of the best transmissions in the automotive business today, even its best five-speed automatic still suffers from this problem. GM's solution is an all-new six-speed that can be used in a variety of applications from rear-drive to four-wheel drive to all-wheel-drive cars, trucks, and SUVs. Able to handle engine torque outputs of 520 lb-ft, the Hydra-Matic Six-Speed will incorporate many new technologies, including clutch-to-clutch shifting, where the transmission shifts gears while under power and eliminates the torque interruption common in regular automatics when they change gears. Additional features include driver shift control (tap up/tap down), automatic grade braking, and neutral idle. We tested the unit in a Tahoe, and it was truly a pleasure. With a gear spread of 6:1, a sixth-gear ratio of 0.67:1, and a first-gear ratio of 4:1, this transmission is perfectly suited to trucks and SUVs. Look for it across the GM's worldwide lineup in 2005 on '06 vehicles.--C.S.