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2.4 Ecotec and 6 Speed Auto

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A few weeks ago, I had to trade my Lacrosse to "fix" some damage that I couldn't file on insurance, because "someone" keeps backing into my car. :huh:

I settled on the Un-Malibu as my new daily driver.

Appearance-wise, I like the car. The exterior is tastefully sporty, and the interior is nice, in an adult sort of way. It actually seems to be what Buick would have done with, it if it were theirs. The stated gas mileage, and my concern about the future of gas prices were key factors for me in selecting this car. The early hailing of this car as the dawn of a new day in GM mainstream products had also attracted me.

My jury is still out on the powertrain. The 2.4 is smooth and powerful for what it is. I was a Quad 4 fan back in the day, and this engine seems worthy of that heritage. But the 2.4 and the new 6T40 A-6 don't seem to be well matched to each other. The engine wants to run in the 3000+ rpm range, but the 6T40 is determined to hold it around 1800. So there's a whole lot of shiftin' goin' on.

I'm finding only limited comments on this powertrain on the web, but there does seem to be a theme of early dissatisfaction with the 6T40. Hunting for gears, lazy shifts, and hard shifts are the common complaints. Reflashes by the dealer are being done in response.

I'm at about 1900 miles now, and am noticing some improvement, I assume because the adaptive technology is learning my driving habits. I've also been making a point to drive the snot out of it in an effort to help it in the "adaptive process" :D Seems to be helping.

At this point, I have to say that the 6T40 is not on par with the A6 in my wife's Milan. The trans in that car borders on amazing - it always know exactly where to be, and you barely feel the shifts. I think I'm recalling that the Milan trans was actually made by Yamaha.

Anyway, I guess my overall assessment at 1900 miles is Satisfied, with some reservation. It would be cool if I could find a GM Powertrain engineer that was interested in getting some input from an informed consumer, and maybe even let me field test some reflashes, but reality says that a pipe dream. C'est la vie........

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That is a terrific engine, the 2.4L 4 cylinder makes 177hp in the Sky, 169hp in the Aura. My second favorite 4cyl after the 2L Turbo DI variant of the same engine.

I agree that nobody seems to like the programming of the 6speed auto. It is confusing because normally GM has terrific transmission controls.

I find this surprising also because I think the transmission logic in the 5speed auto in my CTS is terrific.


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It is confusing because normally GM has terrific transmission controls.

Yeah - it is. My hunch is that they've programmed it the way it is to meet the mileage claim. That being the case, its unlikely that the reflash that would make it drive right will ever see the light of day. Maybe Jet or someone will catch on and come out with an aftermarket module for it.

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Background paper on the 6T40/6T45:

2010Hydra-Matic 6T40 (MH8-FWD)

Hydra-Matic 6T45 (MH7-FWD, MHC-AWD)

2010 Model Year Summary

Hydra-Matic 6T40 / 6T45 six-speed automatic front- or all-wheel-drive transmission

● Six-Speed Automatic Transmission

● New North American Applications: Chevrolet Equinox (MH7, MHC), GMC Torrent (MH7, MHC), and Buick LaCrosse (MH7); Carryover: Chevrolet Malibu (MH8)

● Contemporary On-Axis Design

● Advanced Clutch-To-Clutch Shift Operation

● Tuned For Quick Launch And Fuel Efficient Cruising

● Compact Dimensions Aid Packaging

● Hyper-elliptical Torque Converter Saves Space

● IX Gear Pump Lowers NVH Levels and Improves Hydraulic Efficiency

● Ground And Honed Gears For Precision Fit And Lower NVH Levels

● Unique Input Shaft Eliminates Costly Machining And Adds Strength

Full description of new features and benefits

Six-speed automatic transmission

Two versions of the transverse six-speed automatic transaxle (6T40 / 6T45) have been debuted, featuring a notably wide ratio spread, and the ability to handle different levels of engine torque and vehicle applications. The 6T40 / 6T45 have been designed to address high feature and high value segments with combination of 6-speed, advanced features, and low piece cost. Availability of wide ratio spread allows improved fuel economy and improved performance. The 6T40 / 6T45 transmission has an output chain, and also features a compact low cost 1 piece case.

New applications:

Chevrolet Equinox (MH7, MHC) and GMC Torrent (MH7, MHC) are scheduled to go on sale in the summer of 2009 using the 6T45 (FWD and AWD), which is mated to the 2.4 LAF Ecotec and is rated to handle 315 N-m of engine torque. Additionally, Buick LaCrosse (MH7) will go in production at the end of 2009 using the 6T45, which is mated to the 2.4 LAF Ecotec. The 6T40 / 6T45 will also continue to be offered in 2010 Chevrolet Malibu (MH8).

Carryover from model year 2009 features and benefits are listed below:

Innovative on-axis design

Instead of “folding” the transmission around the end of a transversely mounted engine, which has been one of the dominant GM transaxle design conventions, the 6T40 and 6T45 contain all of their gearing in line with the crankshaft centerline of the engine. The advantages of this layout can translate to a shorter overall vehicle length, more interior room in a vehicle, and lower powertrain height.

Advanced clutch-to-clutch shift operation

To save space compared to “freewheeling” gear change mechanisms, the shifts are accomplished by applying and disengaging clutches simultaneously during each gear change. Sophisticated electronics help enable the precision needed to time the clutches for each shift. The first-to-second gear shift uses a freewheeling mechanism, however, which tends to be smoother during shifts between gears with large ratio differences, such as first and second gears.

Tuned for quick launch and fuel efficient cruising

Because of the wide ratio spread, first gear is a very high ratio, which provides brisk acceleration from a stop. Sixth, however, is an overdrive ratio, which keeps the engine revolutions as low as possible for highway cruising, reducing engine friction losses and improving fuel economy.

Compact dimensions aid packaging

State-of-the-art dimensions enable spacious packaging and enhance potential safety design opportunities. In addition, styling opportunities for lower hood lines are also enabled by the compact dimensions of the 6T40 and 6T45.

Hyper-elliptical torque converter saves space

The 205k, 236mm torque converter in 6T40 (MH8) and 6T45 (MH7) uses a single plate lockup clutch and features an oval cross-section shape, called “hyper-elliptical”. This shape 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 packaging advantages. The single-plate lockup clutch makes use of GM’s electronic controlled capacity clutch (ECCC) technology to help dampen engine vibrations and ensure smooth operation.

IX gear pump lowers nvh levels and improves hydraulic efficiency

A compact on-axis, fixed displacement IX Gear type fluid pump provides hydraulic pressure for the shift events and lubrication. The pump features an IX gear (Drive/Driven) with a machined crescent in the pocket, which reduces internal leakage and optimizes hydraulic efficiency. The inlet jet nozzle feature in the IX gear type pump provides for increased pump suction pressure which has demonstrated to lower powertrain NVH levels.

Ground and honed gears for precision fit and lower NVH levels

To minimize gear noise as well as vibration, the helical gears are ground and honed to ensure exact dimensions and tolerances. With closer tolerances, the gears are less prone to characteristic whining or humming, and overall the transmission operates as quietly as possible.

Unique input shaft bushings eliminate machining

The input shaft requires no machining for grooves to contain fluid seals, which allows the shaft to retain maximum strength for its size and minimize cost.

Low maintenance

The 6T40/6T45 is filled for life with DEXRON®-VI premium fluid, which during normal use need not be replaced. DEXRON®-VI is validated to improve durability and shift stability over the life of the transmission. DEXRON® VI, was developed to have a more consistent viscosity profile; a more consistent shift performance in extreme conditions; and less degradation over time. Internal GM tests have demonstrated DEXRON® VI delivers more than twice the durability and stability in friction tests compared to existing fluids. The DEXRON®-VI fluid was designed specifically and validated for the new family of GM six-speed automatic transmissions.


The concept behind the new six-speed front- and all-wheel-drive transaxle family is to enable compact packaging not possible before with a powerful transverse powertrain layout. The gearsets are on the same axis as the engine crankshaft centerline, which makes the entire powertrain unit much shorter fore-to-aft. This allows chassis designers the ability to enhance crush zones, to increase interior space, and lower the hood line of the vehicle compared to a conventional off-axis transaxle.

The primary difference between two variations of the six-speed automatic transaxle being the 6T45 has greater torque handling capability. The output chain is 1.25-in wide in 6T45, versus 1-in wide for the 6T40. The input gearset of the 6T45 uses five pinion gears, versus four pinions for the 6T40. In addition, the case of the 6T45 is slightly larger and includes a heavier ribbed case for strength.

Three planetary gearsets are used with three stationary clutches and two rotating clutches, which save space compared to freewheeling designs. Freewheeling mechanisms allow perfect timing between shifts, but also take up more space and add more components to the transmission. However, due to the electronic controls, the clutch-to-clutch concept of the 6T40 / 6T45 delivers the same accurate shift timing. Gear changes from second to sixth gear ratios are accomplished with a precise 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, however, is a freewheeling action, where the second gear clutch engages while the first gear one-way clutch spins freely. This allows a greater degree of smoothness at lower vehicle speeds.

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.

The wide overall ratio spread of 6.11:1 allows a “steep” first gear, as well as a “tall” overdrive top gear for low-rpm highway cruising. Acceleration is maximized, as is fuel economy. Engine noise is also lower during cruising. Sixth gear is a tall “overdrive” gear, for example.

The transmission control module (TCM) in the 6T40 / 6T45 allows the modules to exist reliably inside the transmission, where temperatures remain mostly constant compared to a body-mounted module. The smaller size of the module means the transmission case can be more compact. The transmission and module are assembled together, so no additional connections are necessary during vehicle assembly.

The 32-bit transmission control module (TCM) monitors transmission performance and compensates for normal wear in components such as clutch plates, so transmission performance remains consistent for the life of the transmission. The control module also “tests” the components of the transmission following assembly to optimize the interaction of the components. The module is compatible with all future global applications and the design can accommodate different modules. All of the module strategy is developed by GM Powertrain.

The Hydra-Matic 6T40 / 6T45 was developed as part of the small 6-speed transmission family for global applications and is being produced in Asia Pacific region (GMDAT, Korea, and SGM, China) with subsequent manufacture in North America (SLP, Mexico).


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