DMiller wrote:
there are TWO separate D70 Housings. One for Dual Wheel PICKUPS, one for Dual or Single rear Wheel and Specialized bed NOT Dually Pickup. Tires run REALLY close to springs on Second one. Width Difference is almost a full two tires Wide. Different Axles as well.
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Actually, there are at least a dozen different configurations of D70 axle tube lengths.
The chassis-cab ones are what you describe with the tires being almost against the springs, like my F-350.
On most of the SRW trucks, the axle tubes are a bit longer than a chassis-cab and the spring hangers are different, placing the springs farther out from the rails.
On some SRW trucks (and some "dualies"), the frame actually widens aft the cab.
In most instances, "dualie" spring perches are further outboard than chassis-cabs due to the same reasons described above = either the spring hangers are further from the rails, or the frame itself is wider, and in some cases both; so, if one wants to mount a "Dualie" rear-end under a chassis-cab truck, another set of spring perches are going to have to be welded on, closer to the differential = not a good idea if the truck is going to be loaded on account of so much unsupported tube beyond the springs.
There is another axle configuration that is actually more common in junk-yard finds than one would think --- in fact, I have one under my 1978 K20 Chevrolet that I mounted under there probably 40-years ago = Hi-rail RxR trucks.
It is 4' 8-1/2" railhead to railhead; Hi-Rail axles have to be designed such that, when the truck is on the rails, the tires must contact the rails.
I was trying to navigate a very tight turn off of a very narrow road with a really short culvert and huge holes on each side, pulling a 24-foot Gooseneck (24-foot floor length = 12' for the neck) load of cattle; I dropped a hind wheel off the edge of the culvert and snapped that axle shaft when I tried to pull myself out --- of course it was that weird RxR rear-end.
I almost never found a replacement axle shaft; anyone that had a RxR rear-end wanted to sell the whole thing.
Finally, at a huge nothing-but-trucks junk-yard, I found one = for thirty years, they had been using it to drop down into a hole in the concrete to hold the double doors closed; after we had looked at every axle on the place, I spotted their door latch and asked "How about that one ? " ; they pulled it out and we measured it and it was exactly what I needed and is still in there today.
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