rock crawler trans selection

68muleteem

so i live in MN and know nothing about rock crawling. I am working on building one but may have overlooked something. I have a 1990 YJ frame, 2004 4.0l, ax15 trans, northwesr fab doubler, dana300, dana 60 front and rear wirh the front flippef to right side high pinion. 37" tires.

So what i may have missed is if the ax15 is strong enough for this? I may stroke the engine but the overall plab is to give this to mu daughter for Moab and Rubicon.

Any thouhjts?

Skyler-At-Novak

A few things you'll want to consider here.

Yes an ax15 should be able to handle 37's and a 4.0l even if it's a stroker with no issues. It's talked that the original factory AX15 was rated for 300 ft lbs of torque while the AISIN ones available now are rated for 385 ft lbs. It's a very popular transmission for your application. We do make a few components to upgrade a couple weak points on the factory AX15 which you can find here https://www.novak-adapt.com/catalog/transmission/transmission-parts/ax15-parts.html that will help beef up that AX15 a little.

Now the biggest downside to an AX15 is it only has a 3.83 first gear ratio, but with your doubler you should get a pretty decent crawl ratio. But you can also achieve this by going to a transmission with a lower first gear. *That's if you're not needing the overdrive*. If you wanted to look into a truck 4 speed like a T18/T19 or a SM420/SM465 they you can achive that lower ~6:1 granny first gear ratio without even having to use a doubler.

Now we are releasing our NovaDrive in the next few months that would be the best of both worlds in that sense. You'll be able to use a super strong truck transmission with that granny low first gear for crawling and the overdrive for highway driving.

Those are a few things to consider as you are selecting your transmission.

Let me know if I can be of anymore help.

Magneto

Agreeing with Skyler on this. In addition to that, much of the torque that is created (or backfed) is going through your doubler box and Dana 300. So, I think the AX15 will do fine.

As a matter of driving technique, just be conscious not to send nasty shock loads through your powertrain if it can be avoided. That is good advice whether you are using just about any gearbox.

AndyGrewe

I have a SM465 in my CJ5 behind a healthy LS and it's on tons and 40s, it has been in there for 17 years with no issues. This summer I may take it out to have the machine shop check it over but still operating just fine.