Drivetrain questions and concerns

[JasonB]

It's been awhile since I last posted anything but I've been busy with the birth of my second girl. Now she's 3 months old and my oldest is now seven. I'm also a firefighter at to different departments and going to school part-time. But during my off time occasionally I get the chance to tinker on on the Comanche. Here recently I've been working on trying to get my Ford 9 inch in. I'm at the point of setting my pinion angle and butting everything back up.

 

My next big project will be replacing the Aw4 auto with a manual. Not sure right now if I wanna go nv3550 or ax-15. I've heard that the nv3550 is stronger but the ax-15 is more reliable. The nv3550 is also picky on its fluids. I do know if I go with the ax-15 then I'll need the 94 and up due to the external slave cylinder. And I also know that the nv3550 has a better crawl ratio in first at 4.01 compared to the ax-15's 3.83. What do you guys think? Nv3550 or ax-15 tranny and why? New or junkyard or rebuilt?

 

My other question or concern is after the tranny I wanna go low low with my gearing. I've got decent low gearing in my diff with Dana 44 and the 9 inch having 5.13's. I was thinking of doing a doubler setup with the northwestfab doubler kit since I have a spare 231 setting around (price is around 700$ for kit or 1600$ for a built one. Was also thinking of running a doubler with a rubicon case that I can pick up for $1100. Also if not the rubicon case I'd like to run the Tera low kit if I were to keep the 231 (price on the Tera low is around $700). Here's another idea...I've got a ford np205. Is that overkill? Attach that to the doubler and run that? What do y'all think? Would the np205 mate up to the doubler kit by nwf? Any ideas?

 

Let me know what y'all think. If you guys have any suggestions that would be helpful please feel free to post your comments. Thanks

[Eagle]

My next big project will be replacing the Aw4 auto with a manual. Not sure right now if I wanna go nv3550 or ax-15. I've heard that the nv3550 is stronger but the ax-15 is more reliable. The nv3550 is also picky on its fluids. I do know if I go with the ax-15 then I'll need the 94 and up due to the external slave cylinder. And I also know that the nv3550 has a better crawl ratio in first at 4.01 compared to the ax-15's 3.83. What do you guys think? Nv3550 or ax-15 tranny and why? New or junkyard or rebuilt?

 

The AX-15 is also picky on fluids. Having owned and driven XJs and MJs with the BA 10/5, the AX-15, and the NV3550, IMHO it's a no-brainer: go with the NV3550. It's a far better transmission.

[DirtyComanche]

I wouldn't go out of my way to source a NV3550.

 

The Teralow is a pile of junk.  I wouldn't run one if it was given to me.  Go with the NP241OR, It is actually reliable.  The Teralow has an unpublished maximum input speed while in low range, and it's quite low.  The Teralow absolutely won't last behind a doubler.  The NV241OR, well, it should, although you're definitely asking a lot of it.

 

I have a NWF EcoBox and Ford NP205 in my XJ.  Yes, it will mate up, that's the intention of it.  They actually won't recommend that you use an aluminum case behind it, if you really ask.  There is serious downsides to this setup.  You can't clock the NP205 up high enough to get anywhere near a flat belly, unless you're super short or willing to run some terribly uncomfortable race seat, and that's after cutting the entire mount boss off the NP205 and plating over it.  I modified my seat mounts extensively, and spaced the seat up, along with doing a massive realignment and patch job on the floor.  Clocked as is, it moves the driveshaft over a bit to the driver's side vs a NP231, which probably won't cause you any issues, but coupled with my front axle it meant the entire floor had to be cut out and changed.  It also might be hard to fit your typical long arm setup in, but YMMV, my XJ is very low for the tire size (maybe 4" lift at most).  Also, the entire doubler and tcase setup is something in the range of 175lbs (I'd have to look, I have the exact number somewhere), which means you're absolutely not going to get away without having a second mount, and it's just heavy in general (keeping a vehicle light is extremely helpful for everything).  You really will need to go to polyurethane motor/trans/tcase mounts to deal with the torque.  Also, there isn't an actual regular twin stick shifter available off the shelf for this setup, just cable shifters, which I hate, so I spent a bunch of time/money making a twin stick setup for it.  You'll need a speedometer adapter from PATC, I can get you the P/N if you want.  To do it over I'd just buy an Atlas, honestly, I have way too much time and money into this once you figure out all the monkeying around with cutting holes in things, rebuilding things, and fabbing one off parts.

[JasonB]

Ok thanks I have decided to get a Rubicon case. I'm actually meeting the guy tomorrow. He wants 1250$ for it but I've got him down to $1100. He won't budge much further on the price. It came from a rolled 2010 Jk unlimited with 29k miles on it. The case is extremely clean as if it's never been wheeled in the dirt before. Next step is either getting an ax-15 or nv3550. Is there a write up somewhere on doing the conversion? On either one. My concern is not the spline count as from my understanding both the ax and the 3550 have 23 spline output shafts but I'm concerned with the shaft protrusion outward from the case. Will that match up to an ax-15 fine?