12 bolt axles swaps

[Quikshft]

My '71 4x4 has 3.07 gears and 33 inch tires, with the 4speed it cruises the freeway nicely but I tow a small travel trailer and am thinking about trading that for a larger/heavier unit. Gears need to change! It seems the easiest thing to do is swap an entire 3.73 or 4.10 axle into my '71, will any 12 bolt interchange? Are there variations in the spring pad location? If I found a an axle with a five lug bolt pattern would my current six lug axles interchange?
Thanks!
Jeff

[Mike C]

I do think the axle length on the 2x4 and 4x4 are same in the same years. But on 2x4 trucks, the axle widths change 67-69 and 70-72. Also, the spring centers are different on the 4x2 trucks at 42” versus 40” on the 4x4. Not near as many leaf spring 2x4 axles either as 75% of trucks were coil spring in the 1/2 ton.

You do know that the front and rear gear ratios have to match within 1% or so for the 4x4, correct? So if you change the back, you need to change the front.

Good opportunity to do an 8 lug swap with donor axles which are more likely to have 3.73 or 4.10 gears. My Jimmy has a semi-float 14 bolt with 4.10 gears and Gov-Lok swapped in from an ‘86 Suburban and 4.09’s installed in the original Dana 44 and the brake parts swapped on from the ‘Burb 10 bolt front. SM465 trans and 35” tires.

On my kid’s Jimmy with swapped in 3.73 geared front/and rear from an ‘84 K20 Suburban. Factory Gov-Lok rear and we used a ‘79 Trans Am posi unit in the front axle. TH350 trans and 35” tires. Converter slippage should have the two about the same rpm down the highway.

[Quikshft]

Mike C yes I know the front axle needs changing too, has the original Dana 44 there now, but in the 5 years I've owned the truck I haven't had call to to turn the hubs. The front probably needs to be gone through anyhow, I probably would do a ring/pinion swap up there after I find what is going in the rear.

I have also thought about an 8 lug swap, but I've got good money invested in the tires on the truck currently and it seems a waste to throw them to the curb and have to get new wheels and tires on account of my axle choice. I have a certain 'look' going with my hubcaps that I really enjoy at this point - another count against the 8 lug swap but I will consider it. Would this require driveline lengthening/shortening as well?

I understand what you say about the 4.10s though, not likely to find them in a half ton axle? Maybe I'm looking at a ring/pinion job after all?