The Stovebolt Site Forums The Parking Lot '60-'66 Trucks 3 speed with Overdrive

I feel silly asking but Im some what lost.
I found an 1964 chevy c-10 in a pile of Black berry bushes and it only had 44,000 miles on it.
the One thing I dont understand is the Trans...I know its a 3 speed on the tree..but what I dont understand is it says on the owner Identification from the factory build sheet....Eng. No. F0626n witch is a 230 ci. and Trans No. M617 The trans leads me to beleave its a 3 speed Overdrive.....am I wrong?????...and if it is, How the Heck do you ingauge the Overdrive?

Should be a cable under the dash with a handle that says "Overdrive" on it.
The trans code you have listed doesn't come up in the book. may need to look at the trans itself to confirm.

The overdrive engages electrically. It has a solenoid hanging out of the left side of the transmission if you crawl under. Here are the manuals if you would like to read up on them. There should be pictures in here as well:

http://speedprint.com/deves50/overdriveindex.php

Regards,
Steve
New Orleans

I should have been a little more specific. The Overdrive cable is for the lockout for the freewheeling clutch. With the handle out, the freewheel and overdrive are locked out, and it operates like a normal 3 speed. When pushed in, at speeds under 28 MPH, the freewheel allows for coasting without compression braking, which helps save feul at lower speeds. It also allows the overdrive to engage without shock on the system when 28 MPH is reached and you let up off the gas for a second ot two. As far as the electric part, it is on whenever the ignition switch is on, if wired like the factory did it.

I thought I saw something (don't remember if it was on here or not) about removing the oversrive from a three speed and mating it to a four speed transmission... is this possible? I have a spare three speed overdive and an sm420 in my truck, the overdrive would really help, if it's possible. Any ideas, or am I crazy?

I've heard of that, too. But IIRC, you have to use a Saginaw Passenger car 4 speed. Won't work with the Truck 420.

That's kind of what I expected, the housings look a lot different. I wonder if I could make an adapter and find a way to make it work...

66 father/son:
Conversion would be awfully tough. Why not just put the 3 speed overdrive tranny in with a floor shifter? Do you use the granny first in the sm420? The overdrive is awfully sweet! You are only a drive shaft cut away...

Regards,
Steve
New Orleans

I am still considering putting in the 3 speed and switching to floor shift, but if possible I would like to keep the four and add overdrive. That way I would get the best of both worlds and get to keep my 7.05:1 first gear for towing and have the 0.85:1 overdrive to get my rpm's down and my mileage up, plus I would just prefer to have 4 gears available. The other problem I have is that the 3 speed is from a 1/2 ton and the 4 is 3/4 ton, so they have different sized yokes. I've tossed around a couple different ideas about this before, converting the yoke on the 3 speed, swapping the rear end and driveshaft from my c10 parts truck, or modifying the rear end to accommodate the smaller driveshaft. After doing a little more research I found info on adding the overdrive to a four speed, but as Longbox55 said, looks like it's only a simple conversion when you use a 4 speed from a car. But, it seems like it would still be possible to do with my 420, it would just take a little more work. The next step is to take apart my transmissions and try to figure out if/how I can make it work. Theoretically I think I could make an adapter to mount the overdrive unit behind my 420, or have one of my buddies in the machining program make me one. After that I just have to figure out what driveshaft/rear end to use, and shorten the shaft. For this application I would be comfortable shortening it myself, since it won't be behind a real powerful engine.