You gotta remember, these trucks were trying to move in the neighborhood of 20,000 pounds with less than 100 hp, so having flexible choices in gearing was essential.

 

My F4 has a single speed rear axle. According to the Shop Manual, it's either a 5.14:1 or a 5.83:1 ratio.

According to the Parts Catalog, it's a Ford rear axle. The 5.14 is 8T-4209-C and the 5.83 is a 8T-4209-B. That's all I know.

 

Had a look at my chassis catalog.....I'll stand corrected. You probably have a rare axle. I thought most of the single speed axles were 6.xx:1......engines back then didn't have a lot of power so they had to use LOW gears! It would be really nice if someone actually made gearsets for them.

I tried VERY hard to find a gearset for my Eaton 1350 2 speed axle.....I bought a gearset from a wrecking yard guy and it was worse than the one I was taking out!!

I finally found a complete (good used) pumpkin at FleetPride for $795!

They also found me a new (old-stock) gearset that a guy in Oregon had and wanted something like $1300 for! According to them, the only one in the country! but I would have had to replace all the bearings too. It would have been very expensive!

Joblot didn't have any and neither did any other big truck parts places. The Eaton 1350 was replaced by something else I suppose.

I was lucky to find a complete new 12v shift motor and rebuild kit for my shift mechanism so it's going to work nice.

I doubt I'll be doing any shifting "on the fly" though. Won't be necessary with the automatic trans.

 

The super low rear axles are one of the reasons auxiliary transmissions were popular with over the road truckers. The most popular auxiliary transmission I am aware of was the Dana / Brown-Lipe 5331 / 5831: Spicer 5831. One of these can greatly help with road speed.