View Full Version : Differential Ratio Tag??

09-15-2015, 03:56 PM
One of the questions I have about the '48 Willys 2WD truck is the rear end ratio. I can figure it once I get the truck out of the shop and can jack it up and measure, but I am like any other kid - I want an answer now.

I was looking through a bag o' stuff that dates back to the rear end swap I did about 1973 and I found the little plate whose picture is attached. The shape and curve make me think it is the plate that was attached to the differential with the ratio stamped on it.

The plate is stamped 5_375, which could (?) be a 5.375:1 rear axle ratio. The rear end is a Timken rear end and there is no literature that I have found describing those assemblies. For the more conventional rear axles, 5.33:1 is the highest ratio I've seen. This would be close, but I think it would not be a normal truck differential, more likely a Station Wagon than a 2WD truck (but the 2WD trucks may have been geared higher than the 4WD trucks).

What do I have here?

'Hep me, someone

09-25-2015, 10:17 AM
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.


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".

09-26-2015, 12:36 PM
I am no Mechanical Engineer but I think you may have mixed up your gear ration explanations for which ratio gives more torque. The 6.17:1 would be the one that would climb a wall and the 3.54:1 would be your highway gears. In the off road world anything in the 4s is generally what most people go for, it will give you a good mix of Torque and speed.
Here is a website that helps explain Gear Ratios and Torque for the not so mechanically minded.

Thanks for the other info though it is a good post other than the gears I think you may have just miss spoke on the gears. If I am out to lunch then please correct me but that is what I have always been told.

09-26-2015, 01:32 PM

You caught me. I was sitting here and relooking at my numbers and statements and I realized that I had things bass-ackwards. I hoped I'd get it corrected before anyone caught me, but, oh well, ...

I'm going to edit the original post and make a note of the correction.

Thanks - and someone is looking and checking up on me!