With a lot of discussion between Nick and I, I now have what I believe to be a completely unique 14FF rear axle. If it exists, I couldn't find it, and it's such a PIA, I doubt it will ever be duplicated!
It originated under my K5 where it had the old split e-brake cables. The axle that came out from under the Sub was a 3/4 SF 14 bolt with the large 13" brake drums. I was planning on a junk yard foray to liberate some late 14 FF backing plates, but Nick mentioned he had read that the large SF backing plates were exactly the same as the 3/4 ton 14 FF plates (both have 2.5" wide shoes). Sure enough, as usual, he was right!
Nick had also recently flushed out some faulty information we both carried with us. We both thought that you could switch to late pull-off drum hubs and drums to upgrade an old unitized hub/drum axle. Turns out that's false, no idea how we both made that mistake, but I've got an old 3/4 ton 14FF with unitized hubs, and I HATE those things. On the up side, Nick has also been going through some travails with bending his late 14FF axle housings. Through that he learned that some had MUCH thicker (1/2" IIRC) axle tubes. Which axle has which tubes doesn't seem to be quite clear or entire;y predictable on SRW rear axles, but the odds are better with older axles, so maybe I'll get lucky.
All that got us talking, and thinking. Since the lugs pattern is the same, and the brakes are the same, how hard would it be to use that big deep 14SF pull off drum as a slip on for the old unitized hub without the drum? I gathered up my collection of parts from FF and SF donors, and Nick added in a few options including 1 ton (3.5") slip-on drums and a variety of backing plates. With some investigation, it turned out my original collection proved the best suited. I used the 3/4 ton drums, backing plates and shoes (all practically brand new) off the Sub 14SF. And of course the hub from my old 3/4 ton 14FF axle, minus the drum. Nothing else was really close to working.
So, here is what I did.
1) Turn a bevel in the front OD of the hub so it seats fully in the deep 14SF pull off drum.
2) Make a 0.650 spacer to go behind the backing plate. It seats on the original register, provides a new back plate register on the new front surface, and uses minimal clearance (on size) 1/2 bolt holes just as the backing plate uses.
3) As it turns out, the spindle weld is a HUGE PIA as it wanders a bit, and generally comes right out to where the new register needs to sit on the spindle. If you bore the plate to clear the weld, the register will basically fall right off because the larger bore comes up to the register shoulder. So it took a combination of maximizing the bore depth while still supporting the register, then grind off some of the big ropy weld bead to provide the rest of the clearance.
3) Longer 1/2" NF bolts were obviously required. The spacer was bolted to the original flange and then partially welded. The weld is intended to provide both added rigidity, and also an easy reference to see cracks if they form, which would be an early indicator of movement (bad). I often do the same thing with the pinion caps in axle shafts, just a spot from the cap to the yoke so that if it ever tries to start moving, I can hopefully catch it before it spits out a cap and eats a shaft.
That's about it. Doesn't sound like much, but it was quite a pain due to the weld interference, and my trying to grind the weld at an absolute minimum to prevent any possible weakening. The pics blow show some of the process, and the final pic shows the (supposed) one and only early 14FF with pull off drums.
And YES, I know I could have gone disks, and that was considered. But I will NOT abandon good functioning parking brakes, particularly given the purpose for which I'm building this. I have a set of brackets and disks from a late HD AM axle that I may one day fit, but right now I didn't want to replace my 15" wheels and tires, plus deal with all the updated plumbing and brake cable adapters, so this is how I went. When these tires are shot and I go to 16" or larger wheels/tires, I'll reconsider the disk. Maybe by then I'll run across a complete late disk axle, then only need to swap gears and update plumbing/cables...
And given the welds, I would love to wrap it to hide them, but that would likely encourage rapid decay and result in a mandatory replacement in a few years. It's VERY tight where it goes back over the frame and down under the floor, so I don't like the idea of anything that's going to force replacement any sooner than necessary. I did look into the possibility of a loose sleeve like was used on the oil return on the theory that it shouldn't encourage decay like wrap, but didn't find anything that would work for 3". And the expense goes up rapidly with size, so might not be a practical option even if I found something to fit. However, that topic has been a focus of my thoughts, even though I haven't gotten to a solution I like. And that's as far as I've gotten on the down pipe insulation ideas.
