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Just picked up a trailer very slimilar to the one in this thread
78 Toy Box Trailer Wasn't thinking of doing a spring over but really like the look with bigger wheels/tires. Instead of buying new spring perches thinking of using a FJ40 rear axle. Both measure right at 38 & 1/2" between center pins on the springs. While having a axle made would not cost that much I have a number of old 40 axles laying around and a lot of different wheels/tires I could use. Wasn't planning on buyng the trailer and not going to spend a bunch of money when I have parts that would work for free. Since the FJ40s use C clips and have removable back cover rolling the axle and installing the diff back in correct way is simple. Gutting brake parts goes without saying. Does the ring gear need to spin to lube the bearings or can it be locked in place? Removing the spider gears and using a second block on the pinion with keep the axle shafts pushed into the side gear's groove preventing the C clips from coming out. With no spiders gears the ring gear won't move. Would you use a centered diff or the offset diff like on most FJ40s? Centered would look better but offset might be nice on forest service roads that a lot are more two track trail that a centered diff might drag. Best option would be to use a FF axle with the inner axles pulled but that is worth more than a trailer would cost. The axles I would use are old coarse spline axles with very little value.
I'd visit a junkyard and buy a mini-van rear axle and adjust it to fit, then make steel adapter plates to the LC bolt pattern before I'd use a differential. Some of the mini-van's have bolt-on spindles, so can fabricate a simple axle tube & make flanges for the spindles to bolt onto.
Alternately find an old full-float pick-up rear axle and cut off it's axle tubes up close to the diff casting & cut the drive flanges off the axle shafts, then stuff those axle tubes inside a slightly larger tube & add fill & drain bungs. Downside is the 8 lug pattern. I've done that for this trailer, there's 3 gallons of diff lube in the axle for the wheel bearings:
Another option, if you have junkyards with old enough trucks in it/them, is to get a live front axle and use it. My grandad did that in 1959 when he built this trailer, it's a Dodge pick-up front axle of some vintage (& a Ford Model A torque tube for the tongue and axle tube for the stand):
My plan is to use what I already have laying around. Probably have over a dozen loose 40 series axles now. The trailer is useable as it is now. Currently has some aftermarket 14" wheels on the stock mini truck axle. Have no matching spare. I bought my son some new Camry take offs a few years ago for his 99 Camry. Still have his old 15" wheels with old tires worn rotted tires. Could get tires for those and mount the spare in the stock spare tire carrier. Or just install a FJ40 axle non flipped and use FJ40 wheels. While like the look of the large tires on spring over might not go that route to keep the trailer sides lower. Looks like it's about as high as my M416 which everything needs to be lifted over the sides now. Will never haul anything real heavy so doubt I need a FF axle. If I did I have some 40 series FF rear axles already that have spring perches in the correct location and the correct width. Besides the stock springs in these old mini trucks were weaker than those in a FJ40. Shortly after buying my first FJ40 in the mid seventies I went wood cutting with a friend who had just bought a brand new 74 Datsun pickup. I was able to load more wood in the back of my FJ40 than his truck. The springs inverted quicking and frame was on the bumper stops for the axle. Doubt the Toyota would have been much better. He was so impressed he traded the Datsun in for a new 75 FJ40. If I wanted to make a this big project I have FJ40 springs and perches off a frame I could beef it up. Probably modify a FJ40 frame for the mini truck bed and really make it stout. I already have way to many projects and what I looking doing at wouldn't require any fabrication just bolt together.
