(# of forward gears)(Torque capacity)(_T_ransverse or _L_ongitudinal)(_H_ydraulic or _E_lectronic)

So, 31TH is a 3speed, low-torque capacity (small 4cyl), transverse (typically front wheel drive), Hydraulically controlled transmission. That is the neon transmission.

The new system for automatics, is coded to actually describe the transmission. The letter "R" encodes a RWD vehicle. The letters "FE" encode "Fully Electronic", to differentiate the 45RFE from the only partially electronic RE family. The RE units are modified versions of the 904 and the 727. The RE transmissions still use a conventional valve body, but the PCM controls the governor pressure, overdrive and lockup torque converter. For whatever reason
the manual transmissions didn't go to the new designation system.

Here are the Chrysler-built automatic transmissions recently in production, going from memory:

31TH - 3-speed Neon & Minivan

32RH - 3.9L B-van & 4.0L Wrangler

41TE - various 4-cyl & V6 FWD vehicles

42LE - Intrepid/Concorde/Vision/LHS/300M/Prowler

42RE - 3.9L Dakota/Ram & 4.0L Grand Cherokee

44RE - 5.2L (318) Dakota/Durango & Grand Cherokee

46RE - 5.9L (360) Ram/B-van/Dakota/Durango

47RE - V10 & Cummins Diesel Ram

45RFE - 3.7L V6 & 4.7L V8 (2 different second gear ratios)

5-45RFE - 4.7L V8 Grand Cherokee (2 second gears & 2 overdrives!)

I forget what they call the automatic in a 2.4L 4-cyl Wrangler or Cherokee, maybe it's a 31RH or a 30RH? It's really just a light-duty A904. Some of these applications are only for certain model years. For example, the 44RE was used in 5.2L Grand Cherokees from 1996-98, 5.2L Dakota from 1997-99 and 5.2L Durango from 1998-99. The only place in the US market you'll see a 5.2L (318) for the 2002 model year is in the B-van...

Above information is Curtsey Jim Walke