1990 Jeep YJ AX5 Conversion to an Automatic Transmission

[Aspenyj]

I have a 1990 yj with ax5. TBI removed with a dui hei distributor and Weber 38/38. Motor only has 5k on rebuild. I have it running great and it loves to climb and no issues at altitude

problem….clutch release cylinder is leaking that was put in new when the motor was rebuilt. Is there a reasonable auto swap I can do? I’m starting to have sciatic nerve issues and shifting a bunch is crazy painful, so before I drop the trans to redo the clutch/cylinder I thought I would ask as I can’t find much info on this exact subject. I don’t really care about it being a dog, I’m typically never running over 60 and use it mostly for exploring the roads around aspen. Thank you in advance!

[Moses Ludel]

Aspenyj...I would not recommend a changeover from your AX5 manual transmission to an automatic.  First-off, the YJ 2.5L TBI engine (1987-90) did not offer the 904/999 (30RH) Chrysler transmission, which became an option with the 1994 models.  The '94 has the MPI 2.5L four (1991 up), which offers more performance. Your TBI engine's bellhousing pattern is the same, but the electric system and wiring harnesses for the MPI engine are different. The bellhousing pattern for 4.0L and 4.2L sixes is not the same as the four-cylinder engines. An inline six automatic transmission will not mate to your 2.5L engine.

At the very least, you would need to find a '94 or '95 YJ 2.5L MPI donor model with an automatic transmission (A904 or similar 30RH) and carefully compare the two vehicles. Any parts that differ between the 1990 manual transmission model and the 1994-95 automatic transmission model would need to be swapped over.  This gets very busy, including the radiator, chassis and underhood wiring, shift linkage and many other details.

While the automatic transmission changeover is possible and got me thinking about the necessary parts, the amount of labor and footwork to get the parts and install them would simply not be worth it.  If you contemplate doing the work yourself, there is no task that requires more articulation or awkward positioning that a transmission change-out.  To sublet that work to a shop would be considerable hourly labor plus the cost of donor vehicle parts.

It comes down to "can it be done" versus "is it worth doing?"  I would opt for the latter and suggest that the transmission change-over is not worth doing.  Technically, a 1994-up four-cylinder transmission might mate to your engine and transfer case, but that's where the similarities end.

My suggestion, especially in this relatively hot used vehicle market, would be to sell the 1990 YJ intact and find a 1991-up six-cylinder model (4.0L) with the automatic.  There were many 1991-95 YJs and 1997-2006 TJs with the automatic transmission option.  (If you prefer a carbureted engine, the 1987-90 4.2L six-cylinder YJ was available with an automatic transmission option.  I would opt for the '91-up 4.0L MPI engine, which is reliable and less trouble than the TBI fours or a carbureted 4.2L.) The difference between the selling price for the 1990 model and the cost of a 1991-up 4.0L replacement vehicle would likely be equal to the labor and donor parts cost to convert your YJ to an automatic transmission—if that were even practical. 

Moses