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Jeep Differential Ratios - Answer My Own Question
Things you learn after you look deeper:
A. Willys used two vendors for differentials; Spicer and Timken. Timken is the 'clam-shell" rear end, Spicer is the more conventional rear end with a removable cover. Timkens are simpler with fewer parts, but are a pain to set up. They are marginally a heavier duty unit. My '48 2WD has a Timken and the '50 4WD in the restoration shop bullpen has a Timken. No idea of when Timkens finally went away - probably when the Timken bin got empty.
UPDATE
I found an answer to this in the Willys-Overland Shop manual. The official answer was: "Since August 1951 Spicer rear axles have been used optionally with Timken on 4WD trucks. All Spicer axles are Hypoid Gear type. All Timken axles are Spiral Bevel type".
B. A clip from an article in "Four Wheeler" magazine:
"The 4x4s in the 1948 era had no gearing options besides the 5.38:1, but the 4x2s were offered with 4.88:1 and 6.17:1."
C. A dazzling array of differential ratios seems to be available.
I have found the following combinations:
3.54:1 (Gears ?? This is the highway cruiser set!)
4.27:1 (47 tooth ring gear, 11 tooth pinion)
4.88:1 (39 tooth ring gear, 8 tooth pinion)
5.38:1 (Actually marked 5.375; 43 tooth ring gear, 8 tooth pinion)
6.17:1 (Gears ?? This is the set that could climb a wall...WOW!)
I corrected the "Highway Cruiser" and "Wall Climbing" comments after I realized I had them backwards!!!!
Thanks for checking my math guys...
Actually, this makes better sense because the 2WD truck can haul off the house if you get it loaded on the bed. 5.38's make that happen.
D. For you 4WD folks, front and rear sets need to match or really strange and bad things happen
The attached picture is a 43-tooth Timken pinion with a broken retaining bolt head and broken safety wire. A potential disaster if we hadn't caught it.
Remember the mantra "What you see is what you have - trust nothing".