The Stovebolt Site Forums The Shop Area Driveline Repalce 3 sp with 4sp

New guy here. I have a 47 1/2 ton with the 3 speed that I'm working on. I can get a parts 50 3/4 ton that has a 4 speed. I was thinking of using a saganaw 4 speed but have been told that I will have trouble due to the park brake lever. So I'm thinking about using the 4 speed from the 3/4 and using 3:55 rear gears. Would I be smart to just use the 3 speed and 3:55? Also will the 4 speed bolt up to the 3 speeds drive shaft tube? How about the park brake? Can I keep my park lever beside the shifter or not. Thank you for any ideas you have.

there's no reason to use a stock style 4 speed, like any non-overdrive trans, 4th gear is still 1:1, and 1st gear is useless unless you want to climb walls, so you effectively still have a 3 speed

Bill

You are too far away but I have a muncie 4 speed that would let you use all 4

The 3 speed trans would have sychronized gears. The 4 speed may not and have to be double-clutched to shift.

I'm guessing that the 4 speed would be an sm420. The opening in your bell housing will likely be just a bit to small for the sm420. The existin bell housing opening would likely need to be machined out or you be able to use the bell housing from the 50. You will also need to find the correct (different) universal/yoke to connect to your torque tube.

Well dang-it guys, I was thinking my trans issue as a done deal. I guess I'm back to square one. Donf you would be guessing right it is a sm420. I thought I could just use the bellhousing and bolt to the 235. But I see what you guys say if 4th gear is 1:1 I would only gain stump pulling work. Thanks for your answers. One last question I have is about replacing the lever shocks. Could a guy just cut the shock mounts off the 3/4 ton and mount them on the 1/2 ton in the same location they are on the 3/4 tons frame? I'm just starting this project after many years of having other things more important like making a living. Thanks for your help.