Technical 1957 Chevy 3 speed to 4 speed swap

I have what I think is one of those driveshafts....the slip yoke is stuck from rust, but it appears to be about 58" c-c length when it's compressed all or most of the way. The tube is 48" long.

Of course you want to measure your truck to get the right length driveshaft, after everything is put together and all the wheels sitting on the ground.

 

Trans measurement from one I have laying around

The depth of the parking brake is 1 3/4 to the drive shaft mounting surface.
Trans length should come in around 13 inches to the flange. These aren’t very long set ups
case length is listed at 10.5 inches long

 

I found the granny first gear useful for at least one thing. When I was building my house, my 12 year old could load trash, scrap or materials and move them without hurting the clutch or outrunning his lack of experience.

 

Maneuvering around a parking lot with manual steering is pretty nice if you're in granny low....you have time to turn that big steering wheel around as many times as you need to.

 

I used the 1st gear a few times, like when hauling 4500 lbs of scrap steel to cash in. My brother street raced a '64 GMC with one, I saw him wind it up and dump the clutch in 1st gear a few times and launch it. Me, I was watching but ducking for cover.

 

A Saginaw 4 speed just popped up locally for sale. Would that bolt up to the 235 also? As far as my internet research has found it should bolt up to this truck bellhousing? I’m getting more info on the tranny only this thing they put is it has a new hurst shifter on it. I have a Saginaw 4 speed on my 55 wagon with a 327 and it’s worked fine for me. The numbers on the side appear to be 6261886?

 

Should be fine.
My truck 235 bell has a Saginaw 3 speed

 

The Saginaw should bolt to the 57 truck bellhousing. You'll need to use nuts on the lower two bolts. I had to trim the floor just behind the cover plate to fit mine in, and also cut the lever and bend it forward and weld it back together to clear the original bench seat.

 

I'm puzzled with talk of a slip yoke needed? Didn't Chevy trucks in 1957 use an open driveline with a slip yoke? And if his truck has a 3 speed, then a M20/21 or T10 should have the same spline count as the truck 3 speed doesn't it? Seems any of these three trans would bolt right up, and be the same length as the stock 3 speed.

 

The 57 trucks with the normal 3 speed use a normal yoke that slips into the transmission. It's coarse spline, so it won't be the same as the later fine spline transmission output shafts.

The 57 truck with the SM420 4 speed used a bolt on U joint flange, so there is a slip-stub assembly on the driveshaft.

 

If you want to keep the column shift go with a 3spd and o/d (older one so you won't have to screw with shift linkage) or if you're ok with a floor shifter then go with a 5 spd. Both will give you overdrive so you can go on the freeway. Or IF you can find one check out a T170rts (Tremec) from mid 80s F150. You would have to adapt it to your bell but it's a top shift. Or even a Ford 3.03 3 spd with a Jeep T150 top with an adapter to the GM bell.


The driveshaft is kind of a non issue as any good driveshaft shop can make one to your specs.

 

You can still go on the freeway they will just have to wait. lol

 

One on CL in Mesa, AZ. $350 out of a COE with a pto....

Chevy SM420 4speed Truck Transmission w/PTO - auto parts - by owner... (craigslist.org)

 

Guy around the Bay area has 3spds and SM465
https://sfbay.craigslist.org/eby/pts/d/fremont-chevy-truck-manual/7566698588.html

There's also a guy that sells o/d parts, rebuilds transmission or sells it as a whole kit in Seal Beach:
https://orangecounty.craigslist.org/pts/d/chevy-speed-overdrive-transmission/7571531784.html

 

Picked up the Saginaw today. I had another 3 speed laying around so I measured. Looks like I’m gonna be damn close! Be cool if I can use this drive shaft. First picture is the 4 speed second is the 3 speed. Last is the drive shaft on the truck)

 

you'll need to find a fine spline yoke that fits the newer transmission. you can see the coarser splines on your extra 3 speed.

 

Dang. That 3 speed is from a 55 wagon I believe. Not sure if that makes a difference.

 

The splines on the 3 speed changed in 1965 to fine, I believe.

 

Gotcha, makes sense it’s from a 65 el Camino. So I would need a 27 spline fine yoke instead right? Sorry first trans swap

 

yeah. There are a few different types of yokes, so make sure you get one that's the right length and uses the same type of U joint.

 

Like a glove! Now just gotta figure out what yoke I need. Appreciate the help.

 

something like this....or if you can find a used yoke from most GM cars/trucks from the mid 60s-80s, make sure it takes the same size U joint, and has the snap ring grooves in the same place as your old one does.

https://www.summitracing.com/parts/str-u1661