The Stovebolt Site Forums The Shop Area Engine Shop 3-Speed to 4-Speed Swap

I have a 1959 Chevy 1/2 ton shortbed with the standard "3 on the tree" transmission. I am trying to figure out what 4-speed with a granny first I could use. I saw a 4-speed for sale from a 1964 Chevy, but don't know for sure if it would bolt up to the stock I-6 bellhousing. Does anyone know the range of years for the 4-speeds that would bolt up to the '59 bellhousing?

just about any! the 64 would fit - the SM420 was early 50\'s to late 60\'s

Bill

Thanks for your help Bill.

Also, are there any tricks or is it a relativly simple installation? Are there any modifications that need to be done to the drive shaft? Would I need to get a driveshaft from a 4-speed too?

Thanks again

Adam

I think the shafts are the same, as the trans length is the same, and the splines should be too

only difference is the floor pan that covers the trans is flat for a 3spd and has a hump for the 4spd - your 3spd pan won't go on over a 4spd - should be able to find one tho as the 4 speeds were at least as common as 3's, maybe more

Bill

Thanks for all of your help

Adam

I went junk yard shopping this weekend and found a SM420 tranny that was in fairly good shape. On the back of the 4-speed required a U-joint connection for the driveshaft, being different from the splined configuration on the current 3-speed. Also one man said that the clutch needs to be modified. Are the pilot bushing dimensions and splines the same? Is this the right transmission? The numbers on the 4-speed made it appear to be from 1964-1967. Is there a different tranny that would work better or should I go with this one? Also where should the slip yoke be placed in the driveline--right after the transmission or halfway in between using 2 drive shafts? I was hoping this would be a fairly simple swap, but after looking at the 4-speed in person, more problems appear.

Thanks for the help.
Adam

The clutch is the same. If you are using a driveshaft with a center bearing (2 piece), you can get rid of the slip yoke at the tranny end as long as the axle end of the driveshaft has a telescoping section. Just pop the U-joint out of the slip joint and install it in the yoke of the 4 speed transmission. If you have a one-piece driveshaft (no center bearing) get a telescoping one.

You could switch to a 4 speed Saginaw and use the slip yoke driveshaft if you don't care about having a granny first.

I removed a 6 cylinder and 3 speed column shift from a '63 1/2 ton and replaced it with a '67 283 V8 out of a Chevelle and a '65 4 speed from a 1/2 ton. I was able to buy the whole truck (the '65) for next to nothing (this was about 20 years ago). To make a long story short, the floor panel was a perfect fit. That is one of the things I like most about Chevy's is how interchangable the parts are. If I were you, I would look for both the floor panel and tranny at the same time. I would bet that the floor panel is probably different for the Task Force years and may be tougher to find. Unless you don't mind fabricating something.
The first thing I would do is try to find another '59 or 58 to look at.

no Adam, sounds like not quite the right one - there were other applications that could have different driveshaft configurations, like the 3/4 and 1T's, tho it still should be the same at the front, as it would bolt up to the same engines [GM 6 or 8] and bellhousing - with you having a 1/2T you may need to find one from a 1/2T, and they were common 47-59, somewhat less so 60 up, where they were more common on 3/4T

Bill

Thanks for the help everyone.

I might search around for a different tranny or else just measure for a driveshaft configuration that will work.

Adam

i didn't a tranny swap in a 1970 chevy 1/2 ton auto to 4spd and i got everything i needed from a 67 3/4 ton and the swap was extremly easy everything just bolted into place with no problems few things i had to change is the hanger bearing is different from 1/2 to 3/4 ton so i have to drill holes for the hanger bearing and i had to get the back section of the drive shaft shortened bout 1 1/2 in.

Nate