I recently converted my 85 f150's 2wd tranny to a np435/bw1345 combo. It's all working well so far and it's time for me to convert the front axle to a 4wd axle to complete the swap and finally drive a 4wd truck.
I have an axle coming from a realtive's junkyard for 200$ ready to bolt in, but since I want to lift the truck I figure I'll do it while I'm installing my new axle. The rear leaf springs are a set of 2wd, 2.5" leafs that will be staying that way. I can't remember if they have 5 or 6 leafs on each side, I just changed them not that long ago, so theres no need to add a leaf as far as I can see because the back sits a little high already. So I'm not sure which kit to get. Here are the two options i"m thinking of.
To correctly convert from 2wd to 4wd, you are already adding 2" of lift. The springs/shocks are the same up front, but there's a 2" difference in the height of the lower spring seat. This is why you have to add 2" blocks on the rear, so it matches the front.
6" lift is very hard on the axle pivot mounts up front. I know they include new pivot mounts, but they still aren't braced well enough for the stresses that can be placed on them.
In my opinion, if you want to go that high, you'd be better off going to the solid front axle swap right off the bat.
Right now the back end isn't 6 inches higher. It's maybe 3 or so just because there's already more leafs. So I would still probably want to add a small bit of lift in the back to go with a 6 inch front setup, meaning probably new U-bolts.
I kinda see what your saying about the solid axle swap, but I'm a little tight on cash, seeing as Im' going into collage, so I don't have the money to buy many tools, or have somebody fabricate etc. I have access to several good condition IFS setups, but I don't think there's any solid axles to pick from. It just seems like a big expensive unknown mission to swap it to me, and i would rather maybe just get a smaller lift if it came down to it.
Is a 6 inch lift likely to break anything? If so would a 4 inch be a little smarter? I don't plan on any real rock crawling or anything, just maybe a little water, mud that kinda thing that isn't going to scrape or bottom it out. Also if I go with a 6 or 4 inch lift, what is the largest recommended tire size? I think I've seen before that about 35 inches is as much as I'll want to push an 8.8. Any opinions?
I agree with Dave. Do the 4" kit.
If you decide to go to bigger tires later you can always add a body lift (plus you'll need more gearing for anything bigger than 35" tires).
My first tire change was from the stock 29" tires to 33" tires. That was a noticeable performance drop with the stock 3.54 gearing. It was livable though. I don't think going from 29 to 35" inch tires with stock gearing would be livable.
So, my point/advice is that a 4" lift is fine for 35 inch tires and you don't want to go any bigger (tire wise) unless you do a gear swap too.