First off.. there's NOTHING wrong with 4.10s and 235/85-16s.
I run 4.30 gears with 235/85-16s in my tow rig.
60-65mph is a good speed for a low-revving IH small-block 345 with plenty of power to haul the load.
Tires are CHEAP.. just saw an add on my way to work.. $60 for ATs in the 235/85-16 size. Dang..
LR-E, of course.
Sure, you probably won't be hauling at 85mph.. but should you anyhow? A friend with a 460 and 3.25 gears has to run 75-80mph (amazingly, he said that's faster than he likes to pull.. never thought I'd hear that from *him*) because the 460 won't run any slower.
Personally, I'd like to go a *little* taller in tire size to get a little longer "legs" - especially when unloaded, but it's really not bad.
I did pick up a Brown-Lipe auxiliary for the truck, but haven't installed it, and I'm not sure I will yet.
I thought I bought an OD unit, it's really a UD unit.. spec is 1:1, 1.3:1, and 1.5:1
I couldn't find the 1.5 gear - I have a neutral (haven't popped the cover off yet, either).
I'm *thinking* of mounting the brownie backwards behind my t'case (truck is currently 2wd, getting converted to a 60 front and divorced NP205, but I don't want to put the brownie in between.. I'll use the factory NP205 brackets, driveshafts, shifters, etc and keep it cheap).
Running it backwards, will give me a .77 OD gear.
I think it'll split the 3-4 shift (EVERYONE hates that in a wide-box T18/T19) just as well going 3-hi as it would going 4-low.
Bonus, I'll get those longer highway legs.. with an effective 3.30 final drive.
I've just never driven a brownie, and I'm still not real clear on how easy to shift this will be.
If I mount it backwards, I'll probably cheat.. and go with an air solenoid mounted to my T19 shifter for the direct/over switch.
Best spot behind the '205 to mount the brownie is under the front of the box.. and my truck is also a Crewcab, so that's a long ways back. I don't think heating the shifter with a torch will get me what I need.
So air-shift seems a natural.
Just need to make sure I'm capable of double-clutching reliably and consistently with two transmissions in the mix. I can shift one w/o the clutch just fine..
Plus I'll be wanting to slam gears when I downshift from 4-direct to 3-over when pulling a hill.. or upshift from 3 to 3-over. It'll suck to slow down so much I have to back to the gear I was in already..
I have that situation now with the 4spd.
As for mileage.. my '74 IH Crewcab is shaped like a brick.
The faster I go, the worse the mileage gets, so the deep gears just keep me in the power band *and* keep me from pushing too much wind.
I drove the truck with a tired 2bbl 345, wide T98 4spd, 4.30 gears, 235/85-16s, my 16' flabed with my lifted Scout.. tons of parts for sale/trade, tools, camping gear, etc.
14,000lbs on the scales.
Took that from Montana to Colorado to Moab and back last summer.
60-65mph through Yellowstone, Wyoming, Colorado, Utah, Idaho.. slower up the hills with that pathetic 3rd gear..
I averaged 9.5mpg with the trailer, and I think 12mpg on one short section where I didn't pull anything.
As long as I'm teetering on double digits, I'm happy.
The year before, I pulled a lot less weight, using a Scout II to do the pulling, with 4.09s and 33s and a freshly built 345. Probably 10k total gross.
I got 8-9mpg.