TH700R4/NP231C/D44 Swap -
  • 1 Post By kevrags
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post #1 of 1 Old 08-26-2019, 10:22 AM Thread Starter
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1991 YJ Wrangler 
Join Date: Jul 2017
Location: Las Vegas
Posts: 117
TH700R4/NP231C/D44 Swap

I'm just about finishing this up now, so if anyone has questions fire away. As I probably made every possible mistake during this swap, hopefully I can help others out that want to do this one. Short recap:

Started with a D30 swap. I have a '90 chassis, it had a 4" lift and 33s when I bought it. The Jeep is an automatic 4.2, so that meant 3.07 gears, which was a dog. So I bought an ECGS 489 with a TrueTrac and 5.13 gears. That was the easy part of the deal, and I put new BDS springs and shackles on while I was at it.

I bought a 700R4 and had it built by a local transmission shop, and he put in the short 4WD output shaft. I decided to pair it to a 231C because it would connect right up, and I could just mod the skidplate and wouldn't need an adapter. I also got the wider chain and 4 gear planetary. I also wanted to rebuild one as a learning experience, and this allowed me to do that while keeping the Jeep on the road. I put in a JB Conversions SYE at the same time. Modding the skidplate turned into a no go for me. The necessary place for the trans mount stud was in empty air. So, I bought a Barnes 4WD skid and drilled the holes for it, and also had to do some cutting in the back so the 231 wouldn't hit. This is because this setup is a good deal longer than stock. You have to use the gasket between the TC and the adapter as the 700R4 isn't sealed in the back like the TF999 is. That was fun to discover - one of many previously mentioned mistakes! I also bought a JB Custom Fab transfer case shifter. The flush mount model wouldn't fit - it hit the trans - so Jon graciously allowed me to exchange with the billet version.

I bought a Lokar column shifter, but the shaft is so short on the YJ that I couldn't get the bracket for the cable to fit. So I moved instead to the trans mount shifter, which works OK. You have to use set screws and jam nuts to tighten it down in a 4WD application, and the screws were too short for my particular case. I just used a longer bolt for this. Also, the Neutral Safety switch works, but it doesn't disable in 4th - works for all other gears. Looks like too little movement from N to 4th for the switch to engage.

I bought the Novak 4.2- 700R4 adapter, and that all worked just fine. The instructions aren't great, but the were a great help over the phone. The supplied torque converter bolts would rub against the dust cover, however. I bought some 10.9 10mm bolts from the hardware store and they work fine. You have to use a starter from an 80s CJ, and that means also using that external starter solenoid. As my '90 used the starter relay - no Power Distribution Center - this was a simple move the cables over and remove the existing SOL wire swap. You can use the existing neutral safety switch wiring - you just ground one side of the switch. I also used that wiring to supply switched 12V power for the 700R4 converter lockup circuit. I also have a Lokar backup light switch I haven't installed yet. I will splice it into that line to get power to the lights - that's what that harness was originally for, anyway.

All in all, this wasn't super difficult - I'm just slow and had screwups like that gasket, skidplate, and shifter along the way. The driveshaft is about as short as Adams could make it, but it works. My angles are off - ECGS welds the spring pads on for a 4" lift, but the additional length threw that off. I have some 4" shims I'm installing this week. It's probably a better idea to just buy the TC adapter and use a Jeep 231, although the 231C and Barnes skidplate were less than 400 bucks, which about what the adapters cost I think.

I haven't had a change to take it out much yet, but hopefully will this weekend!

Jeepsr4me likes this.
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