KM164

The KM164 is a 5-speed manual transaxle primarily known for its application in the TM Magna (produced between 1985 and 1987). While it functioned as a standard 5-speed gearbox for the driver, its internal engineering was a unique departure from traditional transmission design.

The KM164 was a derivative of Mitsubishi’s earlier "Super Shift" or "Twin Stick" technology. While those older transmissions gave the driver a separate lever to choose between Power and Economy ranges across all gears, the KM164 automated this process specifically for the final gear.

Mechanically, the main gearbox is a 4-speed unit but instead of a traditional 5th gear synchronization on the main shaft, the KM164 utilizes a vacuum-actuated servo. When the driver moves the gear lever into the 5th gear position, a switch triggers the vacuum servo. This servo shifts a separate "high/low" gear set on the input shaft. The transmission remains physically in the 4th gear gate, but the input ratio is increased to a higher "overdrive" ratio. To the driver, this feels like a standard shift into 5th, but internally, the entire input speed to the gearbox has been altered.

This design allowed Mitsubishi to provide a 5-speed experience using a modified 4-speed architecture, saving on the cost of a total redesign during the TM Magna's development. However, the reliance on vacuum lines and servos introduced specific points of failure:

• Vacuum Leaks: If a vacuum hose perished or the servo diaphragm failed, the car would often lose the ability to engage 5th gear entirely.
• Shift Lag: Because the shift relied on engine vacuum rather than a direct mechanical link, the engagement of 5th gear could sometimes feel slightly delayed compared to the crisp mechanical engagement of gears 1 through 4.

As Mitsubishi refined the Magna platform for the TN (1987) series, the KM164 was phased out and superseded by the KM210 transaxle.

Technical data

Lubricant	75W/85W Hypoid Gear Oil
Capacity	2.3 Litres
Clutch Plate Diameter	215 mm
Clutch Operation	Hydraulic
GEAR RATIOS
Final Drive	3.187
1st	4.070
2nd	2.244
3rd	1.467
4th	1.105
5th	0.855
Reverse	4.109