Thanks to everyone for your help and advice. Since I'm not an expert on differentials, I'm still gathering input, before spending any real money, or committing to a single solution. I know that I can bolt a 55-62, 1/2 ton diff/carrier (GM 55T) in my 1942 axle, with only minor changes (Stovebolt tech article). If this gets me a 4.10 ratio then that will be OK. Unfortunately the GM55T carrier that I have on the shelf is too badly worn, and no longer usable, so I'll have to get another. I've also been told that a later 1960s 3/4 ton diff/carrier, (with 3.90 ratio) will also bolt into my 10 bolt 1942 axle. Using the later 60s carrier would also require that I buy modified 30 spline axle shafts, to fit my 1942 housing (another $400).
The major disadvantage to using the GM 55T carrier is that parts for these truck differentials are becoming just as scarce as parts for my 1942 axle. The advantage to using the late 60s 3/4 ton diff/carrier, is the availability of repair parts.
Not being an expert, I'd like to ask if anyone can confirm that the later 1960s, 3/4 ton truck differential & carrier, will bolt into my 1942 3/4 ton axle housing? Just looking for a 2nd opinion. I'd also like to do this without modifications to the OE housing.
Since any of these mods will be quite expensive, I sure would appreciate confirming this information, before I spend a lot of money.
Aside from swapping a later model carrier/diff into the 1942 housing, has anyone put a later model axle into a 1942 3/4 ton? If so, what rear end did you use (year, model, gear ratio, etc)? Was it modified in any way? If so, what modifications were required?
Finally, I've also been told that simply going to a larger overall diameter tire will give me a lower RPM at higher speeds. I know this is true, but I'm running a 29.4 diameter bias ply tire now so, not sure how much of an increase in diameter is available out there, while continuing to use the OE 6 lug (on 5.5), 15 inch artillery wheels.
In doing this upgrade, I really want to keep an OE look for the truck. Being a novice at rear end swaps, modifications, and repairs, any confirmation of the possible solutions I've described above, or any additional advice/information, will be greatly appreciated. Thanks guys. Have a great day.
