Re: \"Boxing\" frame on pre \'76 CJ
I don't know how common it is to box it, but I'll throw in my thoughts...If the frame is thrashed (rusted out, etc.) boxing it will only prolong it's misery, not solve it. If, however, the frame is in good shape, adding additional support would be a good thing...For some. There are some who believe that a flexy frame is good, because they get extra articulation from frame flex. Even for these people, reinforcing critical areas (engine mounts, suspension mounts) would be a good idea. I fall into the "I'd rather let my suspension be the suspension and my frame be rigid" group of people, and I'd want my frame to be as rigid as possible...so boxing it sounds like a good idea. The only problem with boxing it is that you then get collection of all sorts of moisture, mud, and crap inside, that you can try to keep cleaned out...but it will eventually rust, even if you've got it painted. This is a longer term worry... If I were building an ideal frame, I'd avoid boxing it...you can then run stuff inside the framerails with ease (fuel lines, brake lines, air compressor lines) and you can still reinforce critical areas and add extra frame beef...you can use larger channel and go outside the existing frame, use smaller channel inside the frame, or use plating on the outside or inside of the frame. Hey, how many semi's have you seen that have C-channel frame? And how many with boxed frame (I've never seen a boxed semi-frame). The benefits of strengthening it are that you'll never have to worry about it again...it'll be good if you do it right. Difficulty? Well, to do it right, you'll have to be stripped down to the frame.
Once again, at the very least, you oughta reinforce the frame in the area of the motor mounts and suspension (spring and shock) mounts...in addition, you probably should reinforce the areas where there are body mounts, and areas where the frame bends. On something as tightly packed as a jeep, you're pretty much down to reinforcing everything...
As far as as the 90:1 goes...
NP435 tranny, so it's about 6.5:1, right?
What are you running for a t-case?
What size tires are you going to run?
Assuming that you want to be able to drive it on the street, I'd try to figure out what size tires you're going to run, and then do some calculations to figure out what kind of axle gearing would be acceptable on the road. From there, you can multiply your axle gearing by your first gear...Divide 90 by that number, and you'll know what t-case low range you'll want...unless you've already got a particular t-case picked out...
So if you're gonna run 4:11's, you'd need a t-case with a low range of about 3.35...which means either a teralow conversion, or an ATLAS II. Even with 4.56's, you still need a 3:1 low range... Running a D20 t-case, you'd need something like 7:1 axle gearing to get 90:1 crawl ratio...so you're gonna need some low t-case gears. I could be wrong on the NP435 1st gear...is it 6.5:1 or 7:1? That'll change the figures a bit.
Is your D44 the stock D44? I'd search some old posts for durability reports on the D44 with fewer splines. And what are you running for a front axle? 90:1 through a D30 with tires over 32-33" will spell doom according to many of our resident experts (EXPERts because they've EXPERienced blowing up D30's with low gears and big tires...small shafts, small pinion, small u-joints...big problem).
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Moneyless, Will weld for jeep accessories.