Right, Eric, I understand that doubler is in addition to xfr case not a replacement. I don't plan right now to be doing rock crawling; plans can change, but let's just say it's beyond what I see at least for this truck.
My wording was loose - all I meant was if you have a pretty deep ratio (4.88) and you go into 4x4 Lo, then unless I'm mucking up the math here, you have (in 1st gear) 2.47 x 4.88 reduction or about 12:1 and yes of course it's irrelevant to highway speeds, you wouldn't even be in 4x4 at all on the highway (well - snow maybe - which we don't get any more - side issue). Compared to 3.73 in 1st is like 9:1 so changing the rear end (uh, and front) ratio gives you about 30% increase in reduction. If you had 3.08 (unlikely, but just for discussion), and for some reason put in a doubler (like, you didn't know wtf you were doing), as far as rpm's it would be pretty close to the same as putting in 4.88 with no doubler.
Now I could be resting on some false premises here. I keep reading about this stuff and the way I understand it, the more I can keep my rpm's up, it causes less stress on the drivetrain and less chance of overheating the trans and xfr case and differentials. I haven't looked at the torque/hp curve for the 4.0L engine but if it's like most then at really low rpm there's not lots of either. I don't understand why low rpm causes the overheating but I'm just taking that on faith so correct me if I'm wrong.
Highway speed per gear per rpm per tire size just comes into it when I ask the question, what will 4.88 act like on the road. With the .75 overdrive ratio I think it would be ok. Assume here I would never go over 70 +/- anyway and have no interest in doing so, if I ever hit 80 on the freeway it would be unusual and probably only to stay with the flow of traffic like around Atlanta they drive crazy fast and going 65 can cause an accident. So I do want to ask the question, what will my rpm be at that speed and do I accept that as ok.
One thing that's an unknown to me right now is, if you have a manual trans, you know exactly what your rpm's are because there's no slop in it. I went through all this some time ago in looking at trans for Daytona coupes, where you typically have a 6-speed manual and tons of power (say 460 hp) in a 2400 lb car. Here they normally use 3.73 rear end and I have charts that tell me for the given tire size what's my rpm per gear which tells you the theoretical top speed without burying the tach is like 230mph so, completely different issue, I'm just saying the math is available for manual trans but for auto trans it's not necessarily "locked up", there's the torque converter, etc, so speed in gear isn't necessarily a simple matter of the math and how that all works is beyond me right now. I suspect if the rpm's off-road never get to the point of transmission lock up (meaning, you have the actual ratio of the trans's gears), that probably wreaks havoc with the torque converter. I'd want an additional trans cooler but that doesn't help the xfr case or diff's does it.
So there's a bunch of issues some I understand some I don't. What it comes down to is, when I'm off road (very limited experience) I like to not be tearing around because I'm doing it to a) get to secluded places and b) enjoy the ride, so I like to go along sometimes at a snail pace, or, I'm going slow up a steep road with deep ruts down the middle and a precipitous drop off one side so I'm picking my way real slow. Both up and down so trans braking is nice, don't know if auto is a minus for that, probably, but I was told in general auto is nicer for off road so that's what I got. Not to say I don't sometimes give it some gas on a nice straight stretch, but I try to stay sane about it.
For the street, I imagine a 4.88 could light up the tires (talking stock 31" tires here). You might not want to floor it, it could cause a lot of stress on the axle/springs, I'm just saying, it would no doubt improve acceleration, I see that as a potential side benefit for street use. I don't think you can get a deeper ratio and I don't think I'd want deeper. Summit Racing has the 4.88 ("only 2 left!") and I was tempted to think omg I better order it... a bit premature - they're probably available multiple places but you need that reverse toothed one for the front, I found that too, so I think you can get them and probably can later if/when I go that route.
The other thing is lockers. I read all about the Aussie lockers and they seem like the cat's meow, they're always active, ok for the street, but way better than lsd. The only thing that confused me was they were saying coast around a turn and I think that might have been in the testing after the install because if that was a restriction it would make no sense at all.
So I could see putting in 4.88 ratios and Aussie lockers and that would be streetable and super off-road capable. It would be possible to do that (with 31" tires) and not change anything else on the truck, though when you're that far into it doing a lift might be in the picture because everything would be apart anyway, but, you could do just the ratios/lockers and later on do lift because it seems they are separate things. Even if I don't raise the truck, the ratio and lockers would give me a lot of extra traction so for sand, mud, hill climbing in dirt/rocks, it's a big improvement. Other things come into it - shift kit, torque converter, I mean if everything is apart I'd say do those things. You'd want to consider where (rpm's) and how (firm, soft) it shifts.
From a practical standpoint, even though I have the 2 trucks, I don't want my shop hogged for months nor the truck out of commission for extended periods. I can't put lockers in my lsd rear end anyway. I doubt I can find 4.88 rear end out there (used), probably can't even find 4.56, so it's beyond swapping out parts. How I see it is, find a decent axle, tear it apart "on the bench". Take my time rebuilding it and replacing anything as appropriate besides changing the ratios and lockers. The Dana 35 has to come out too (or find one) and have its ratios/lockers done. Then there's the trans, maybe I do nothing with it, maybe it needs something, are shift points affected, I don't know. These are hard things to do, they are saying you need hydraulic bearing press, so maybe some has to be farmed out. The point is if I can get parts to rebuild then swap them into the truck, it sounds way better than having the truck torn apart, can't move it, shop is monopolized, can't drive it, easy to get discouraged, vs working as time permits without the truck torn apart and not rushing things. Glad now I didn't sell the Mazda.
Do I want, or is it even possible, to go Dana 44. I think the Dana 35 is fine from what I've been told here. Not concerned about the rear 8.8", I think it's rugged. In a rebuild probably want to replace all bearings/seals/whatever as appropriate. Not worried about the 4.0L it's gutsy. Might do the injector coils etc at some point, don't know if it matters, it runs great. Once in a while I just floor it, don't know if that's smart but it's fun and I figure if something's going to break let's have it happen close to home and "it burns the carbon out of it" which is I'm sure total bs but that's what we used to say.
Maybe I want to put disc brakes in the rear, I don't think it's necessary or very helpful, just throwing that in.
I'm having a hard time sleeping lately so I'm up and down in the middle of the night reading about this stuff as much as I can. It's a learning curve. I just feel confident in saying, I can probably do everything I would want to do to the truck to make it awesome and still be out of it for something like half the price of a new Ranger, including the sunk cost of the truck itself. A new Ranger with everything I'd want on it is like 43k then you have the insurance, sales taxes, property taxes, higher registration, etc. And it still wouldn't perform like what I described for upgrades and wouldn't have the soul of a '97. That's the whole reason I got the '97 is I asked questions first and was guided to that gen and, yeah, it's not super rare but I assert that it's hard to find a really clean low (125k) miles Ranger that vintage, that said, like has been noted doing the upgrades I mention wouldn't make it less saleable but moreso, to the right person. Though the chance of me selling it after all that would be like zero. Anyway, one thing that pointed me to the '97 gen is you -can- do things to it and also after having the Mazda and seeing how easy it is to work on compared to most other things (e.g., new Ranger) that also made me think, ok, older Rangers rock, I like them, just, the Mazda doesn't have 4x4 and I found I love off road.
I know I'm talking about some things that are hard to do but I tend to choose stuff that's hard, but do-able. Do you know how hard it is to do miter joints on top of dovetails? It's hard!! But I do it and I do it well, it just takes care and patience and the right tools and methods, so I'm not scared and I like projects where you have tangible results (vs computer programs that I did for decades, fun, but kind of "so what" afterwards). Now I can do what I want and one thing I cannot stand is doing nothing it drives me nuts I have to have a reason to get up in the morning and keep my mind going. I'm used to working with very close tolerances so I get it about backlash and bearing clearance and all that. If I have to farm out some work to somebody I trust (good luck there) I will. I have a good hired wrench available. I think it can happen. Anticipation is a big part of these kinds of things, and the work itself is rewarding, and then after all that you actually have something you can use, what can be cooler than that?
No way to talk about these things briefly is there. Thanks for your help and per usual, poke holes in the tentative plans. I got a list of stuff in front of me now that needs doing on the truck regardless - manual hubs, get the door sticker, check slight fluid drip/leak, so on. But everything works on it, so good starting point for upgrades.
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