2012 HYDRA-MATIC 6T40 (MH8) SIX-SPEED AUTOMATIC HYDRA-MATIC 6T40 (MHH) SIX-SPEED AUTOMATIC (eAssist) HYDRA-MATIC 6T45 (MH7 FWD, MHC AWD) SIX-SPEED AUTOMATIC Vehicle Applications Buick LaCrosse (MH7) Buick LaCrosse eAssist (MHH) Buick Regal (MH8) Buick Regal eAssist (MHH) Buick Verano (MH8) Chevrolet Captiva Sport (MH7) Chevrolet Cruze (MH8) Chevrolet Equinox (MH7, MHC) Chevrolet (MH8) GMC Terrain (MH7, MHC) Product Highlights 2012MY introduces the all new “Gen 2” Transmission controls architecture in GMNA vehicle applications. The new controls enable improved efficiency and significantly improves shift responsiveness. Overview Six-speed automatic transmissions are integral in GM’s initiative to offer vehicles with excellent fuel economy and driveability. Designed for FWD and AWD applications, they are used in many of GM’s newest and most popular models, including the Chevrolet Equinox and Buick Regal. The special MHH version is used with Buick LaCrosse and Regal models with the eAssist system. The 6T40 (MH8) and 6T45 (MH7, MHC) share many components. The 6T45 is rated for greater torque capacity due to specific component enhancements over the 6T40. Each is part of GM’s family of technologically advanced, fuel-saving six-speed automatics. The transmissions share an overall 6.11:1 gear ratio spread, which contributes to their signature balance of fuel economy and driveability.
Gear changes from second to sixth gear ratios are accomplished with clutch-to-clutch action, where the clutch is engaged in one gear at exactly the same time it is released in another. The first-to-second upshift, uses a freewheeling mechanisim, where the second gear clutch engages while the first gear one-way clutch spins freely upon release. This allows a greater degree of smoothness at lower vehicle speeds. Adaptive Shift Controls Adaptive shift controls include automatic grade braking, which commands the transmission to remain in a lower gear if the vehicle is decelerating or coasting on a downgrade. This takes advantage of engine braking to prevent unwanted acceleration. This reduces the need for the driver to brake during a hill descent. The control module receives input that monitors brake pedal usage, vehicle acceleration rate, throttle position, and even whether a trailer is connected to the vehicle. Space-Saving Hyper-Elliptical Torque Converter The torque converters in the 6T40 (205 mm) and 6T45 (236 mm) use a single-plate clutch and features a “hyper-elliptical” oval cross-section shape. This design reduces the thickness of the torque converter, reducing the space it needs and keeping the overall width of the engine and transmission as narrow as possible, for underhood packaging advantages. The single-plate lock-up clutch uses GM’s electronically controlled capacity clutch (ECCC) technology to help isolate engine vibrations and provide smooth torque converter clutch apply and release operation. “IX” Gear Pump A compact on-axis, fixed-displacement IX gear-type fluid pump provides hydraulic pressure for shifting and lubrication. The pump features an IX gear (Drive/Driven) with a machined crescent in the pocket to reduce internal leakage and optimize hydraulic efficiency. The inlet jet nozzle feature in the IX gear-type pump provides for increased pump suction pressure, which helps optimize noise and vibration characteristics. Ground and Honed Gears To minimize gear noise, as well as vibration, the helical gears are ground and honed to ensure precise dimensional control. With good dimensional control, the transmission operates with exceptional quietness.