The Stovebolt Site Forums The Shop Area Driveline 1942 3/4 ton Suspension Swap

Has anyone replaced the rear end in the 1941-46 3/4 ton truck? While I love my truck, I'd like to go to a better gear ratio (OE is 4.55), and upgrade to modern shocks. I'm running a 1962 235, with dual carbs, Offy intake, and Fenton headers. Behind the 235 is a 1984 T5. Since I don't do much heavy hauling, and I'm in the South Jersey flatlands, I don't really need a 4.55 gear ratio back there. In doing this, I want to keep my OE 15", 6 lug wheels for an original look, so that limits the options a bit. I'm thinking that something around a 4.10 or 3.90 would give me a little better performance, and reduce cruising RPMs a bit.
I'm sitting on the fence between rebuilding my OE 42 rear, and swapping it out for something newer. Any experiences with the early 40s 3/4 ton, that you care to share, or recommendations for 6 lug axles to consider, would be greatly appreciated. BTW, thus far, everything I've done to modify this truck has been bolt on, and I have the OE components on the shelf, if I ever want to return the truck to a stock configuration. Thanks in advance for any help/advice.

You might be happy fitting a '56-'59 diff , 3.9 ratio, made for your 235 , six stud etc .

I did this on my '40 .

Have you driven the the truck with the T5 and the 4.55 rear end yet?
I ran a 235 with T5 with .72 overdrive and a 4.64 Nissan rear end and 28" tires and it was very driveable up to 70 MPH.
I switched to 215 85 R16 tires (31") and it is now all that I could ever dream of. 1st gear is more usable now (it was on the granny side with the 28" tires). When shifting into gears 2 through 5, the engine is right on the money of the optimal power band for this engine. No lugging at the begging of the shift, and no screaming engine when its time to shift into the next gear.
You might be pleasantly surprised with what you already have.
Carl

Thanks for the input Carl. I have driven the truck with the T5, and it performs as you described. My desire to go to a 4.10 is due to the Granny gear feel of 1st, and the desire to lower RPM at the higher speeds. Do you have a photo of the 16" wheel and tire combination you're using? I really want to keep the OE look of my Art Deco artillery wheels.

Thanks Dusty. The more I research this issue, the more I lean towards using the 55 diff I have on the shelf. Many advantages for someone who wants to keep the stock appearance of the truck. I've ordered NOS side gears, spider gears, and a new cross shaft. I have a 3.90 R&P set I can use, and the carrier will bolt into my 1942 axle. With all new bearings and seals, this should give me the performance and reliability I'd like to achieve for the truck. The truck is not a hot rod, but more of a resto-mod, with all bolt on changes. Gives me the advantage of being able to change this back to a bone stock truck, if I chose to do so in the future.

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.