I plan on doing a 3.5" suspension, 1" body, either 33s or 35s
I'm wanting to build my bronco to be able to drive several hours to either the mountains or beach and then take it off roading.
I was leaning towards the AX15 kit because it'd be a new transmission but second guessing myself if i should go with the NV3550 because of the gearing.
So I think my real question is, for what I'm wanting to do, is the AX15 going to be that hard to learn to drive both on and offroad?
Or lets say i do go with the AX15 and instead of the Dana 20, going to the atlas II t case to help with the lower gearing for off road?
I don't think you could go wrong with either one. Or for that matter, any of the other ones being talked about. But just from your description and not knowing you or your driving habits personally, I'd say just work with the AX15 and don't worry about the minor differences. In part because of the "new" aspect, in part due to the higher torque rating, both of which seem good reasons and no real negatives for you.
The lower first gear would seem a benefit (it's why I chose the 3550 over the AX for myself) but the 351W will help with that when it comes to letting out the clutch. And the fact that your trail needs are not going to be particularly stressful either, the need for the lower gearing is not really high and the AX should be fine.
Either one is a huge improvement over the manual trans that would have come stock!
What about that engine though? Stock? Modified? Fuel-injected? Those also make a big difference in your other choices. Maybe even including the transmission if you have a real fire-breather under the hood.
You're right on the money with the low-range benefit of the Atlas being a good way to compensate for just about any differences in off-road gearing. But here again I doubt you'll find it necessary.
The downside to that logic is that, if you do stick with the 20 at first and decide later you would rather have had the lower gearing, you have to go back through it and swap the 20 for the Atlas. If you're doing this stuff yourself, perhaps not a big deal. But if you're paying a shop to do it, then do it again, it takes on a higher level of frustration. Easy to sell the old adapter though, so at least some of the cost is mitigated.
Frankly though, if the cost of an Atlas is not intimidating right off the bat, then putting one in right from the get-go takes the cost of the adapter out of the equation, saves you a bit of money (in spite of the obvious higher cost of an Atlas over a simple adapter) and gets you that lower gearing that might (or still might not) come in handy. I love Atlases, but don't really think it sounds like you'll be needing one just from the tone of your description.
Do you think you might ever decide it's just too much fun and start doing harder and harder trails? Or just a daydream and the simple dirt 2-tracks leading to a hunting lodge or lake going to be the way things go? If the latter, stick with the 20 and pocket the Atlas money for the cool paint job.
Best thing you can do no matter what, is just like someone said and choose the right differential gearing for all-around best performance in your arena. This can make up for many shortcomings elsewhere. Both on and off the road.
The minor difference in gearing between the two boxes you mention is not going to be enough to either make or break your off-roading prowess (until the trails get more tricky) nor your ability to learn how to shift. Or more accurately, how to get rolling from a stop!
The lower first gear of the 3550 would be slightly more forgiving of getting a Bronco rolling, but the difference between the two first gears should not be hard to deal with. Especially with the 351 and the correct diff gearing.
So you probably can't screw up the transmission choice with either one, unless you screw up your ring-n-pinion ratio choice first.
To that end, check out the calculators online (here's one such:
https://www.yukongear.com/calc_rpm.aspx) and see where you think you'd like to be. Don't fear the gear, but no reason to over-do it either for a mostly street driven rig.
4.56 comes to mind for 33's, and probably the 35's too. With the right engine of course.
Or with 4.88's being the choice if you think you'll spend more time off-road than you originally thought. Or even 4.11's if you just want the lower engine speed on the highway and your engine is strong down low and burns clean through EFI. And you don't happen to live where the roads are really hilly.
Otherwise stick with the 4.56 I would think.
What other equipment will you have that might make the Bronco really heavy or have greater rolling resistance?
So you can see that asking your questions and making specific decisions up front will help, but every time you waffle back and forth over tire size though you change all the other parameters! So make that decision and adjust the other stuff accordingly.
It's all about the tire size and R&P ratios...
Good luck!
If your head ever starts to hurt with all the choices, step back and and relax... While you try to choose a paint scheme!
;D
Paul
