The Stovebolt Site Forums The Shop Area Engine Shop Transmission Question

I have a 1950 3/4 ton truck with a 4 speed in it. The engine was swapped to 235. I have a 1948 1 ton rear end in it. My problem is it is wrapping all kinds of RPMs at 45 miles an hour. I cant get it up to 55 without the motor sounding like it will over rev and fly apart. I have the transmission that matches the rear end out of the 48 sitting on the shelf. I am wondering if I swap the transmission to the one that originally went with the rear end, would it give me a better ratio? Or was this rear end just not made for today's speeds? Thanks

They are both direct drive in high gear. Doug

Going back to the 3/4 ton rear would help some (4.56 ratio compared to 5.13). Either way, they're not really meant for high speeds. The best bet would be to find a '67-'72 3/4 ton 3rd member with the 4.10 ratio. It's a bolt in for the current 3rd member.

Bill is right.

Your other option is an overdrive transmission like a T-5.

But really you are running stump pulling gears in the rear and that is where your problems starts.

Don't you have to modify the drive shaft or have it reworked fot that swap Bill? That is the 67-72 3/4 ton pumpkin swap! Also, can you use a 3.something ring and pinion in that newer carrier???
I wouldn't know where to start but I sure wish we could pull all of this 3/4 ton rear info together into a complete tech tip since it comes up so often.

Denny Graham
Sandwich, IL

I just went through this whole thing. Had to shorten the driveshaft a little, and 4.10 is the highest road speed option, but I am completely satisfied with the results.
Before: 5.14 final. 45mph = fastest sustainable cruise. Comfortable road speed was 35 - 40 mph.
After: 4.10 final. Relaxed and comfortable at 50 - 55 mph, fastest sustainable = somewhere over 60 mph.
BIIIIIG difference! This was a farm truck, now it's a road truck.

you could just do what i do: drive slow and PO everyone behind you. it was the cheapest and easiest for me.

I've heard that there is a 3.9 or 3.7 gearset available, but its rare and hard to find. It wasn't used very many years and was little used in those years.

If I knew the details I'd share them. Some searching here is likely to turn up more information. What you are looking for is a late 60's early 70's C-20 with an automatic. Big block suburbans seem to me the most likely place to find them.

It might be less trouble to swap rear axles.

Thanks for the help fellows. I was making sure there was nothing I could bolt in that I already had on the shelf to make it better. I think I will drive it the way it is for now, but when I get a chance I will put a higher rear end in it.