Drive Train

The following 1991 models have a new EGS automatic transmission shift program along with a recalibrated transmission and a changed rear axle ratio.

Model Final Drive Ratio
Old New

535iA 3.91 4.27

735iA/iL 3.91 4.27

750iL 3.15 3.64

85OiA - 3.64


The lower final drive ratio provides improved acceleration off the line while enabling the use of a new "EGS Map" which is biased towards early upshifts at light throttle, yielding increased performance without sacrificing fuel efficiency. During light throttle duty cycles, 4th gear can be reached as early as 40 mph with the converter clutch engaged.

More important than the actual acceleration time is the heightened feeling of "power on demand". As the system detects the driver's desire to accelerate (by comparing throttle opening to road speed and gear position), it is programmed to downshift sooner than previous models to make maximum use of the engine's power. The cars are still equipped with a kick-down switch; however, in most driving situations, the transmission will have shifted to the lowest gear permissible for a given road speed before the switch is activated.
The major changes to the transmission include the torque converter and converter clutch solenoid. Due to the lower rear axle ratios, the torque converter stall speeds have been decreased to between 1954 and 2135 rpms with the M30 engine, and between 1815 and 1980 rpms with the M70 engine. These figures will be slightly lower (50-100 rpms) if the engine is not yet broken in. The lower stall speed converters are not interchangeable with previous models. The frequency of torque converter clutch engagement/disengagement has increased on these models. In order to ensure the reliability of the converter clutch solenoid, the construction of the solenoid has been changed from aluminum to steel.

These drivetrain components are certified by the EPA together as a complete system. These parts are not compatible with past models and fault codes will be set if parts are interchanged between systems.