The Stovebolt Site Forums The Shop Area Engine Shop Transmission swap 3 speed to 4 speed

I have a 65 C-10 with 3 on the tree. The original transmission has been replaced with a Saginaw 3 speed. I want to replace that one with a saginaw 4 speed on the floor. Any advice on the conversion? The driveshaft has already been shortened, but I understand that the bench seat may be a problem. If so what bench seats will fit?

Thanks

what's your purpose in switching to a 4 speed, do you need a granny gear? only problem with a bench seat [any one] may be that you'll have to custom bend a shift arm

Bill

I have a 65 C20, the previous owner replaced a 3 speed with a 4 speed. No issues with the seat, but the top of the transmission comes up through the floor. He did a hatchet job though. There were two different floors for those years: low hump for the 3-on-the-tree, high hump for the 4 speed.

With the Saginaw, most shift linkages available put the shifter too far back for truck use, which makes it interfere with the seat. There's really only a few choices on making one work, 1-cut a notch in the bench seat for clearance, 2 swap to bucket seats, 3 the custom bent shifter that red58 mentioned. There is a shifter from Patricks that clears the seat, but it is made for '47-'59s, I don't know if it will work with a '60-'66 body.
If you're looking for either a granny gear or a higher road speed, a 4 speed will not help. If you want the lower first gear, you'll want the SM420 4 speed, along with the different trans cover GrimGreaser mentions. If looking for better road speed, you should take a look at a T5 5 speed, which has an overdrive gear. That trans also has a provision for placing the shifter close to the same location as the SM420, so it will clear the seat. That conversion has been covered extensively, doing a search on this site will give you all the info you need.

The 3-speed just doesn't have the correct gear ratio...either too high rpm for second or too low rpm for 3rd. I though the 4 speed would make the truck more comfortable to drive around town. I'm not looking for highway driving...only have the 230 engine.

Thanks red58

Thanks LONGBOX55, I'll research those transmissions. The 5-speed looks appealing. Will it bolt up to the housing on a 230 or is a conversion required? I was trying to avoid multiple conversions and understood that the Saginaw transmissions are the same length. The driveshaft has already been modified for the 3-speed.