From Mitsipedia

The KM177 (also known as the F4A23) is a four-speed electronic automatic transaxle built by Mitsubishi. It was used in fuel-injected TN Magnas.

Early into the Magna's life, MMAL knew that the KM175 could not handle any more torque than the carburettored Astron II produced (200Nm) as it was designed to withstand the 2.0 Litre 4G63 SOHC used in the Galant (which produced 170Nm of torque). This extra 30Nm of torque is likely what led to the failure of so many KM175s.

When the TN EFI was introduced, MMAL decided to look for another automatic transmission as it feared an extra 5Nm (making the amount over what the KM175 was designed to handle 35Nm or 20%) would be too much for the KM175 to handle. As such, the KM177 was introduced.

The KM177 was similar to the KM175 and as such includes a damper clutch in the torque converter which causes the converter to lock at low vehicle speeds. The operation of the clutch is controlled by the Transaxle Control Unit.

As with the KM175, gear selection is electronic and is controlled by solenoids activated by the Transaxle Control Unit. The TCU uses information from sensors which provide information on vehicle speed, throttle position, engine coolant temperature, gear lever position, engine speed, transfer shaft speed, overdrive switch and kickdown drum speed.

The main differences between the KM175 and KM177 are:

  • Torque convertor stall speed dropped from 2200 - 1600 rpm to 2100 - 2500 rpm
  • The end clutch was redesigned and could handle significantly more torque
  • Stronger transfer shaft, planetary gears, kickdown band and differential
  • Deletion of the oil pump adapter
  • External transmission oil cooler

The KM177 can not directly be installed into a vehicle with the KM175 as they use different plugs. The KM177s are square, whilst the KM175s are round. The transaxle control unit is also different for the KM177.

The KM177 was superseeded in the TP by the KM177-6

Technical data

Lubricant Mitsubishi ELC-4 ATF, Castrol TQM-SP, Valvoline Type M-II Special
Capacity 5.8 Litres
Torque Convertor Stall Speed 2100 - 2500 rpm
Final Drive 3.705
1st 2.551
2nd 1.488
3rd 1.000
4th 0.685
Reverse 2.176