I just swapped axles in a 61 f350. I was open to all possibilities to get faster gears. I looked for 1 ton pickup axles, motor home axles, older Rockwell 1750lb axles, and even the import cab over trucks.
I was switching from 4.56 to 3.54 or 3.73, depending on tire size and wheels.
I found that the new one ton pickup axles are often expensive, and the newer ones from a diesel will have faster gears like 3.54 or 3.73. The older ones from a gas engine are slower.
Motor home axles are usually a Dana 70HD, Dana 80, or a Rockwell. They are almost always 4.56.
The older Rockwell axles like form a Ford f700 are only available with slow gears, I looked at about a dozen and they were all slower than 4.56.
The little cab over trucks are only available with 5.xx and slower, although I forget if I found one with a high 4.xx, but still slower than 4.56. There are no gears available to go faster for those axles.
I ended up using a 2001 Rockwell Meritor 15,000lb axle from a freightliner. It has 3.73 gears. Two gear choices are available faster, but are about $2,000 and a few months lead time while they make them for you. The axle I found has 14" disk brakes and 19.5 or 22.5 wheels are available to fit.
Use this site to find the right combination of gears, OD, and tire size. You want your engine at it's peak torque rpm while cruising at your preferred speed in order for best fuel economy
http://www.drivetraindirect.com/t_gear_calculator.htm If you do find a Dana motor home axle, which is probably the cheapest axle of your choices, you may need to change the gears and also the carrier, this will cost about $600 minimum in new parts.
I'll have pictures soon of the conversion I just did.
Grigg
