2007 Hydra-Matic 4T65 (M15/MN7/M76)


2007 Model Year

Hydra-Matic 4T65 four-speed electronically controlled automatic fwd or awd Car and Truck transaxle




            • There are no changes for the 2007 Model Year




The M15/MN3/MN7 uses DEXRON® VI fluid, which is validated as “fill-for-life,” and requires no maintenance. The M76 uses DEXRON® VI in the transaxle case and BOT190M1 in the power takeoff unit. This is also fill-for-life under normal operating conditions. In addition, the ability to tailor the transaxle to specific platform requirements with the wide range of available ratios ensures the transaxle is operated as designed. Finally, the chain and sprocket drive system and the premium material used in the gear sets contribute to very high durability and no requirement for maintenance under normal operating conditions.




The Hydra-Matic 4T65 (M15/MN7) was introduced in 1997, and has applications from mid-sized to large front-drive sedans and minivans, using V-6 and V-8 engines. It is a two-axis automatic four-speed transaxle with electronic controls, and features a unique dual chain and sprocket configuration that runs quieter than a single chain design. A stronger version of the chain, with heat-treated pins, is used with V-8 applications. In addition, for V-8 applications the starter motor is moved from the engine side of the engine/transaxle coupling to the transmission side, and the input sun gears are made with a process that increases durability, and the final drive shaft gets a shot-peen process that strengthens the metal of the shaft. The final drive planetary differential gets a larger pinion gear carrier, and the park position gear gets a stronger bearing. In addition, all pinion gears are made with a process to increase their strength.


The M15 is available with two different size torque converters (245mm & 258mm), while the MN7 features a heavy-duty final drive gear set. The M76 is the M15 with a unique power take-off housing driven by the differential ring gear.


There are three final drive ratios and three sprocket ratios, allowing nine separate overall ratios. There are almost two dozen families of electronically programmed shift schedules, and the total number of calibrations, or “maps,” telling the transmission when and how to shift is almost three dozen.


New applications were added for the 2006 model year, including the Buick Lucerne (M15) and Terraza (M15, M76), the Saturn Relay (M15, M76). New V8 engines were added to the Chevrolet Impala and Monte Carlo and the Buick LaCrosse, which required that the shift performance be tailored to the engines with two new torque converters, both 258mm in diameter. The new torque converters allow more efficiency and durability with the new engines. For the 2006 Model Year, the Terraza, Pontiac SV6 and Chevy Uplander, Malibu, Malibu Maxx, Impala and Monte Carlo were added. The shifter was also improved for easier position selection.


Also for the 2006 Model Year, a new transmission fluid, DEXRON® VI, was developed to behave more consistently during temperature and other environmental variations, as well as to provide even lubrication of the moving surfaces of the transmission throughout its lifetime. This fluid is validated in all versions of the 4T65 transaxles.


Driver selectable modes are available to allow drivers to select a “normal” mode for imperceptible shift feel, as well as a “performance” mode with quicker shifts that occur at higher RPM for improved acceleration. The operation of the 4T65 is controlled by either an Engine Control Module/Transmission Control Module combination, or a Powertrain Control Module. These controllers compensate shift timing for normal wear of components, which offers consistent operation for the life of the transaxle. If a driver manually selects a low range, but then fails to upshift at higher speeds, the control systems protect the engine from over-revving by automatically shifting to a higher gear. The controllers also reduce engine spark during abusive shifts that occur during “rocking” maneuvers, such as trying to extract the vehicle from a snow bank by rapidly shifting between forward gears and reverse gear. The control systems protect from overheating by automatically applying the torque converter clutch to reduce heat build-up from fluid shear, and a “limp home” mode allows the driver to operate the vehicle at reduced speed in the event of a transaxle control failure.


Upgrading to Engine Control Module/Transmission Control Module configuration is continuing on a gradual phase-in schedule. The latest module is the T42 Transmission Control Module (TCM), which was introduced in 2004 for the Rendezvous application of the 4T65. This module has more memory and faster processing speed than previous modules, and the new configuration increases the flexibility and capabilities of the vehicle electrical architecture. The T42 utilizes “C” language common software (C-series) which provides a modular structure with stand alone architecture.


GM’s proprietary Electronic Capacity Controlled Clutch (ECCC) technology dampens engine torque pulses and provides a smooth engagement of torque converter lock up, and is integral with all 4T65 applications.


To improve noise and vibration characteristics of the entire engine/transaxle unit, bosses have been added in several places on specific 4T65 housings to accept struts and brackets that connect the different engines to the transaxle. These pieces serve to dampen vibration and noise of the entire powertrain unit. Four different locations for the bosses are cast into transaxle cases and different locations are used for each specific engine and platform.




The M76 features a power-take-off unit that routes power through a hypoid gearset to a rear drive module, which provides torque to the rear wheels. This on demand all-wheel-drive system is called Versatrak. It incorporates automatic engaging rear axles that take torque from the front axles depending upon the difference in the amount of slip between the front and rear axles, and in the difference in the amount of slip between the left and right rear axles. This is a mechanical and hydraulic system that operates independent of driver input, and has electronic controls to monitor temperature and the use of different diameter spare tires.