You may or may-not also need to have your drive lines shortened/lengthened or replaced.

 

in a word, no. Just depends on what you want. You can find AX-15 rebuilt for a lot less money AND it's a direct replacement. I've never seen/heard anyone doing the swap you are considering. I've been wrong before, but from what I know, have read, and such, I would say that is not really an upgrade at all. Just a different transmission that happens to match the bolt patern for the engine.

Just my $0.02.

 

I have the NV3550 and it may handle a bit more torque, but when ICON builds you a CJ3B for $100K it will have an AX-15 mated to en ecotech 4-banger.

 

I have been told the other way around, that the ax15 handles more torque...

 

No significant upgrade from either tranny to warrant a swap on it's own. Each has their own quirks. That said, the NV3550 does have a lower 1st gear ratio. Since you're going to be changing out transmissions anyway, it's something to consider.

 

My dad has an ax15, I have an NV3550.

I find that even though my dads has issues with second gear grinding, it shifts MUCH faster and smoother than my NV3550. The NV3550 does require a different type of fluid too, thats a little less common than normal gear oil.

If it were me, Id get which ever was easiest and cheapest to install. Both are decent for a Jeep I find.

 

Is there a noticable difference in the 1st gear ratio?

 

I would say not at all.

The AX15 is 3.83 and the NV3550 is 4.01

 

I am no expert but a close friend is one of the owners of Rockland Standard Gear a company here in NY/NJ that rebuilds all sorts of trannys/ tcases/ axels/ for truck, cars, jeep, whatever. He told me on several occasions that the AX15 was a better trans simply because they last longer with less maintenance and are easier to rebuild and get parts for. He also said they will handle slightly more torque making them good candidates for v8 swaps. I have had 3 jeeps with ax15s (2 tj sports and a ZJ) and one with a NV3550 (Rubi TJ), the AX15s always shifted harder but never gave me trouble, I got water in 2 of them and just drained and refilled with 0 issues lol. My 3550 doesn't like to shift unless I change the fluid often however, if its got clean fluid it shifts like butter and has better day to day manners.

That being said my friend George (the owner of RSG) has an 03 sport that he swapped an ax15 into because he preferred it over his NV3550. Personally I think it just preference and if you have one or the other just stick with it. They are both proven and tested to be very reliable. As far as gearing I do not think you will ever notice a difference.

 

its a direct bolt in swap. same mount, same shifter. no driveshaft issues.
the nv3550 is rated to handle a little more torque.
i think the ax15 shifts better. find the cheaper of the two and buy it.
i swaped out my ax15 for an nv3550, cause my syncros were getting tired.
i got a new nv3550 too cheap to pass up. they are about the same.

 

I ran the ax15 for a couple years and when having some mods done I had the chance to pick up a nv3550 at a good price. I think it made a big difference / improvement in shift quality. I thought it was way smoother than the 15 and didn't grind in 2nd.

 

Im going to rebuild my ax15. I don't think the nv3550 is worth the extra cost

 

That depends on the cost of rebuild. I payed $650 for the 3550, drove it for a year and sold it for the same price. I'm sure you can rebuild one cheaper, but in my case it was money well spent for the newer Trans.

 

Hate to hijack a thread, but are the shifters actually a direct swap?

 

I do not think so, I know hurst and BNM make shifters for one or the other and they are not compatible. I had a hurst in my old tj with an ax15 and miss it so ******** much lol.....