AX15 / Explorer EFI diff gearing suggestions

[dmoses42]

I've been looking through different threads trying to figure out what axle gearing to use in my build, still in the parts-gathering stages. Ol' girl is a 1972 Explorer Sport with that ever-attractive Durango Tan! As noted, mild Explorer EFI build (just hopping up the cam a little, stock GT40 heads) with an AX15 to replace the 3 speed manual, 32-33" tires and a stock Dana 20. No plans to ever go to 35's, those left with my youth, too old and fat for that now. Looking at a 2.5" lift with the recommended 1" body lift. I've seen some saying they are happy with 4.11s, most are saying 4.56 is what they like. My old girl is mostly going to be a street girl, but won't mind some mud under her nails if you know what I mean. I do plan to do some highway / interstate driving for 400 mile trips, maybe more. I've been wondering if anyone has tried running 4.30s with what I'm trying to do. I was also curious about the available gearing difference between the front and rear, closest I've found for the Dana 44 in the front is 4.27s, and 4.30 or 4.33 for the 9" in the rear. My head says 4.27 and 4.30 shouldn't be an issue since I won't be running them on pavement at the same time, but figured I'd get general consensus from all the knowledge on here. I'm not into rock crawling and all that, youth took that desire, too, when it left. I just don't want it screaming running 75 on the highway or not enough get-up when I want to mash on it. I hope that makes sense. Any comments, experience, or education is welcome. Thanks in advance!

 

[bax]

I ran 4.11 with your set up. (33'' tires) It worked well but I felt it was just a little under geared for around town. I went to 4.56 and am much happier. Interstate is just fine and I pretty much just 1 to 1 in town. The 4.30 is not enough change from 4.11 to really see any difference.

 

[DirtDonk]

What gearing are you running currently? The 3.50 or 4.11?
If a 4.11 already, then don't change a thing until you drive it for awhile on the street. And personally, even if I had a 3.50 in there now, knowing what I know about my Explorer engine and overdrive automatic, I'd keep the 3.50's until I had a chance to drive it.
I have no doubt I'd rather have something in the 4's than the 3's, but I would not hesitate to at least drive it that way. My current setup with only little 31" tires would handle 3.50's pretty well I bet. But I have 4.11's ready to go in place of the current 4.56 anyway.
Just in case...

But I'm also in a bit of a pickle, knowing I want to go to a larger tire like you're contemplating. I have 2.5 + 1 and uncut fenders. Thinking I can find a compromise tire and maybe even keep the 4.56's ultimately.
But that's the beauty of the rear 9" differential. It's easy enough to swap back and forth (I have an already built 4.11 3rd member) between the gear ratios and see what fits.
And like we've recommended so many times before, change the rears first and then drive it. Leave the front driveshaft out in case someone accidentally shifts the t-case into 4wd while the hubs are locked in, and drive it.
You'll know pretty soon whether it's a good fit for you or not.

And yes, the few points off in gearing is not an issue off road, and is how the Broncos came anyway. The difference is a Dana diff in the front and a Ford diff in the rear. Rarely (if ever) do the numbers match exactly. Which is why it's not recommended for dry street use. Only slippery or off-road conditions.
So yes, 4.27 and 4.30 is a match.

Paul

 

[dsmelfi]

I've got a Blueprint 306, ProFlo 4 EFI, AX15... my rig is a bit bigger with 3.5” suspension & 2" body so I'm running 35s... But I geared to 4.56 and it's perfect! 2nd, 3rd and 4th gears just get up and go when I hit it and 5th is perfect for a solid 75-80mph cruise on the highway with room to easily hit 90 if needed.

 

[dmoses42]

Paul,
My old girl isn't operational now, I've just been gathering parts to start the restoration process. I bought her in '93 or '94 when I was stationed in North Dakota, drove around up there and when I got off active duty, drove her back to Georgia. Drove a bit down here then smoke came out of the steering column one day, so I figured I'd put a new turn signal switch in to get her going again, then found where someone had cross-threaded the nut holding the steering wheel on and I put it on the back burner. 2 decades later, the original brake lines had rusted off the master cylinder and I decided to just do a full restoration. So I'm getting my parts together and separating them by tasks. As she sits, she has 3.50 gears, but last time I registered her was 1999. So right now I'm gathering parts for my axles, and I really doubt she's going to move under her own power until the drivetrain is done. I guess unless someone chimes in with first hand knowledge of how the 4.30s behave, I'll just go with the 4.56s in the rear and not build the front until after I see how I like the 4.56s. I'd still like any feedback from anyone with experience with what they have. Thanks to Bax and dsmelfi for your input, I appreciate it. Y'all are easing my mind a bit.

 

[76Broncofromhell]

3.50s will work fine for what you have. The AX15 doesn't have a massive overdrive so you will still be in the power band with 3.50s at 70. Bronco Fudds love to tell everyone to overgear because they are stuck in 1975. It's kind of comical. You don't need 4.30 gears with 33s. If you aren't rock crawling or towing a trailer, I would try it out with the 3.50s and then if it bothers you, move to a deeper gear.

As for in town performance, the AX15 has a 3.83:1 first gear compared to a 2.99:1 in the 3 speed so getting started will be a lot easier than you remember. You have fuel injection so your low end torque is a vast improvement over a 2 barrel 302 from 1973.

For reference I am running a 1989 EFI 5.0 in a Toyota with an AX15, 4.11s and 35s and I would say it's a tad low geared for street duty. I ran another rig with a similar setup (5.0 and ZF) with 3.73s and 37s and it was also manageable for its use.