starting this thread to document my swap instead of doing it after the fact when my memory is fuzzy.
Background: my NSG370 pops out of reverse. In street use it's tolerable but it's exacerbated when backing against any resistance, such as uphill (like the 8% grade on my driveway) or if a tire has to climb a rock or a log on the trail. This is annoying at best, and at worst could be dangerous or life threatening if on a narrow mountain switchback in Colorado. I had an AX15 in my '99 TJ Sahara, I liked it better, and the cost of swapping is almost the same as a rebuilt NSG370. (this thread is not for the purpose of rehashing the relative merits or issues with either transmission or of changing from one to the other)
Parts Required:
(1) New AX15 transmission. I got mine from Novak (their pn TR-AX15) because it was $50 less to ship here from Utah than from Advance Adapters in California. It comes with the shift tower and a new shift lever that isn't quite the same as OEM. It's straight, seems thicker, and is unpainted. I'll have to bend it to my needs. It also came with a shift knob that looks decent enough but not stock by any stretch, and has Novak's name on it.
https://www.novak-adapt.com/catalog/transmission/transmission-packages/ax15-package/
https://advanceadapters.com/transmission-ax15-4wd-new-unit-750-tip-boxed
(1) Advance Adapters 712590L AX15 bellhousing with 05-06 crankshaft position sensor location. My understanding is the bellhousing comes with both CKPS locations so it's backward compatible. The Advance Adapters bellhousing includes all the stuff that goes inside the bellhousing except for the flywheel, disc and pressure plate. At time of order they gave me an expected ship date of May 17. Based on the backlog they had at the time she seemed optimistic that it wouldn't move out but left open the possibility that it could. Because of course, COVID.
https://advanceadapters.com/4559
(1) Luk clutch kit 05-065. Not technically "required" but at 127k miles it would be dumb to have the transmission out and not replace the clutch. I'll have an extra pilot bearing and release bearing because I couldn't buy the clutch or the bellhousing without them. I'll freshen up my flywheel with some emery cloth.
https://www.amazon.com/dp/B000CICYZ4/?tag=wranglerorg-20
(1) pilot bearing remover tool. if I forget to get it before I start the job I'll use the bread trick.
The bread trick didn't work, so I went to the zone and got the pilot bearing tool.
(1) Weatherpac connector for the reverse light switch. The NSG370 uses a Mercedes connector that will be cut off and replaced. I got this 5-pack from Amazon
https://www.amazon.com/dp/B076H987BN/?tag=wranglerorg-20, and this tool to crimp them
https://www.amazon.com/dp/B071KFLY43/?tag=wranglerorg-20
The AA bellhousing kit came with most of the hardware (9 bellhousing to transmission bolts, 3 clutch dust cover bolts, 2 slave cylinder mounting bolts, 1 05-06 CKPS mounting bolt) but for some reason did not include the following, which I sourced from the local Ace Hardware.
(4) 7/16-14 x 1" bolts to mount transmission mount bracket to transmission. The NSG370 used M10x1.5 here. Get flange bolts if you can, use washers if you can't.
(1) 3/8-16 x 2" bolt for starter (again, NSG370 had a metric bolt here).
I got a regular hex head and a washer, and had to grind a couple of threads off the length of it because it was bottoming out in the bellhousing before tightening up. I don't think 1-3/4" would have given enough thread engagement, but maybe if it was a flange head and you didn't have to use a washer.
(1) M10x1.5x50 countersunk bolt. I'm welding this on top of the shift lever after I cut it off as the one that came with the transmission was comically long.
I used two additional hex cap screws to attach a cover over the 97-04 CKPS hole, and it's not listed in the bellhousing kit parts list but I have no memory of purchasing them. I think they were the same thread pitch as the 05-06 CKPS, which would make them 1/4-20, but you'll want to make sure.
What's the same or close enough:
1. Overall length. When I had the two side by side last year I measured them as within 1/4", so my driveshafts will be fine.
2. t-case interface. NP231J's all had the same bolt pattern and clocking for the run of the TJ. My t-case has a long input gear that originally came from an AX15, so in a way it's going home, and my front case half came from a 2000 Cherokee with an AW4, which was an identical replacement for the front half that I broke a bolt tab off of during an SYE install in 2019.
3. clutch slave cylinder.
To be considered:
1. The inner shift boot of the NSG370 is basically at tub level, which I expect will conflict with the enlarged section where the upper and lower shift lever meet. The AX15 boot sits proud of the tub to be above this point. My NSG370 boot is trashed anyway and I'm not gonna buy a new one for $180, but if I ditch the hard plastic outer section for an older one, then I think it moves the mounting point for the front half of the center console, so then I'd need one of those from a 2001-2004 TJ. I like the 06 console better so I adapted a <99 AX15 shift boot onto the hard plastic floor plate from the NSG370.
https://www.amazon.com/dp/B01BGJM830/?tag=wranglerorg-20
2. I understand the NSG370 transmission mount will bolt up but will interfere with a couple of bolt heads on the AX15, so I need to notch it out to clear those. No problem.
....lets just say I'm knocking on wood.. .hard and often, that she stays as is.
