Aisin AS66RC / AS68RC / AS69RC

Aisin's AS-series six-speed automatics — the medium-duty gearbox behind the Cummins in Ram trucks.

⚑ It is the alternative to Chrysler's own 68RFE, and which one a truck has changes everything about diagnosing it. The Aisin is the heavier-duty option, usually specified with the higher-output engine and the cab-chassis models, and it shares no parts and no failure pattern with the RFE. Establish which is fitted before reading any symptom.

The number is a torque rating — AS66RC to AS69RC in ascending capacity — the same convention as Aisin's B-series and Getrag's G numbers.

Heat is what kills them, and towing is what makes heat. A cooler, a temperature gauge and a shortened fluid interval are the three things owners who work these trucks fit; without them the fluid degrades long before the stated interval.

Their reputation is excellent when serviced and poor when not, which is a statement about duty cycle rather than about the gearbox.