Jeff,
historically, the torque converter, by increasing the torque on startup allowed fewer gears, but it had slippage which resulted in a loss in fuel economy of about 5% versus a manual transmission. Mercedes had their first application of 3-speed automatic transmissions with torque converter in the 50s in the 300 series, but that transmission was purchased from Borg-Warner.
When Mercedes decided to build their own transmission, due to the emphasis on fuel economy they chose a design with fluid dampener (hydraulic clutch) and 4 gears (although startup usually was in second). These had less slippage and the fuel economy penalty was less than 2% in comparison to a manual transmission.
With the later introduction of the lock-up torque converter, this difference in fuel economy penalty was minimized, and the next generation of MB automatic transmission also had a torque converter.
You cannot put a torque converter on an old hydraulic clutch automatic transmission; they were not designed for the torque peaks.
Klaus
1969 280 SL
