Hydra-Matic 4T65-E (M15/MN3/MN7/M76) Car Transaxle


2004 Model Year Summary


·     New applications: Pontiac Grand Prix with L26 and L32 engines and Buick Rendezvous AWD with LY7 engine

·     Driver shift control feature added

·     Sun gears coated to increase durability

·     P05 PCM (powertrain control module) & T42 TCM (transmission control module) introduced





The Pontiac Grand Prix (GMX367) 2004 model year powertrains include the 4T65-E (M15) with the L26 3.8L V-6 engine, and the 4T65-E (MN7) with the L32 supercharged 3.8L V-6 engine available with or without driver shift control.


The Buick Rendezvous (GMT 257) will add the LY7 3.6L V-6 engine to its all-wheel-drive model in the 2004 model year. This required a unique transaxle case to accommodate the engine mating surfaces.



The L32 Grand Prix application features driver shift control. This feature (when enabled) gives the driver the ability to shift gears (up or down) using steering wheel mounted paddles. To accommodate the wider range of operating conditions and enable required driver control, the valve body/spacer plate assembly, 1-2 manual shift band, and the fourth gear clutch assembly have been modified. Abuse protection preventing engine over-revving by selecting too low of a gear for a given speed has been incorporated into the calibration and control software.



The input and final drive sun gears are “Balzer” coated to improve durability associated with the duty cycle requirements as a result of the new Rendezvous engine and transaxle. Balzer is the name of the proprietary coating supplier.



The P05 powertrain control module (PCM) is being introduced in the Grand Prix application of the 4T65-E. The P05 PCM is a major upgrade to the P04 PCM with more memory, faster processing, smaller size, and more advanced electronic technology.


The T42 transmission control module (TCM) is being introduced in the Rendezvous application of the 4T65-E. This new engine control module/transmission control module configuration for the 4T65-E is part of an initiative that increases the flexibility and capabilities of the vehicle electrical architecture. The T42 utilizes “C” language common software that provides a modular structure with stand-alone architecture.




The M15/MN3/MN7 uses DEXRON III fluid, which is validated as “fill-for-life,” and requires no maintenance. The M76 uses DEXRON III 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-E (M15/MN3/MN7) was introduced in 1997, and has applications from midsize to large front-drive sedans and minivans. 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.


The M15 and MN3 are distinguished by two different size torque converters (245 mm & 258 mm respectively), while the MN7 features a heavy-duty final drive gear set.


There are three final drive ratios and three sprocket ratios, allowing nine separate overall ratios. There are 22 families of electronically programmed shift schedules (increased from 20 available last year), and the total number of calibrations, or “maps,” telling the transmission when and how to shift is 34 (an increase from 33 last year).


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-E 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.


GM’s proprietary electronic capacity controlled clutch (ECCC) technology dampens engine torque pulses and provides a smooth engagement of torque converter lock up.



The M76 features a power-take-off unit that routes power through a hypoid gear set 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.