I have a 1966 Plymouth Belvedere with an automatic transmission. What type of fluid does the transmission use? I have been told some types will mess up these old trannys.

Originally, it was plain Dexron ATF. I would drop and clean the pan, replace the filter, drain the torque converter, adjust the bands with a torque wrench, refill with approx. 13 qts. Of Dexron, start the engine, and pause for 5 seconds in each gear as you shift the gear selector. Adjust final fluid level, when the transmission is warmed up and in Park.