The Stovebolt Site Forums The Parking Lot '60-'66 Trucks 3 speed w/ overdrive anybody?

Greetings, I would love to do a little research before making a purchase but unsure where to start. I am interested in adding overdrive to my 66 chevy in-line 6. A quick search on CL found me a couple possible options. What should I be looking for to be certain one of these OD tranny options will work with my stock set-up? Thanks for any input!

Do you know what transmission you have now? Is it a four bolt side cover ,or a seven bolt side cover? You want to get the same one that you have, that way will be a simple take one out, put the other in.

Check out info online re. the T-5 BorgWarner, have one in my 46 behind a 261 and it's great.

I know it's the stock 3 speed transmission, for a 250, I will crawl under it to look closer next chance I get. Thanks Tommy

Unless it has been changed, the stock transmission would be a short tail shaft SM318. It has the 4 bolt side cover and a non syncro first gear. 66 was the first year for a full syncro Saganaw overdrive transmission to be offered for that truck. They are rather scarce and priced accordingly. The earlier factory overdrive, 55-65 is a SM319 is more readily available. It would also match the shift arms for your truck. Any overdrive change will require a driveshaft modification as they are longer than the stock transmission. There are electrical components and a pull cable required for each of these units to operate.
Fred

To function as designed, a BW overdrive trans needs a cable-operated lock out installed, a kick down switch on the throttle linkage, a relay, and some wiring. The OEM relays and kick down are a little scarce, but the function can be duplicated with a Bosch-style relay and a micro switch with a little tinkering to fabricate a mounting bracket for the switch. Don't get persuaded to try to substitute a toggle switch for the right wiring- - - -it's very simple to make it work right. The wiring setup would be the same for either the Saginaw of the Muncie transmissions. If you have a choice, try to get a Saginaw. That synchronized 1st. gear is very handy, even if you have to modify the shift linkage a little to use it. I can provide a wiring diagram for the Bosch relay and micro switch if you find a transmission to buy.
Jerry

Thanks for the input guys, this really helps.

I have read your (Fred and Jerry's) replies several times. I'll know more about what I'm working with when I finally meet the seller. Another commodity that is scarce right now is bread! I hope I can find you again when that time comes. Truck on.

If you have a 66 it will not have a muncie . It will be a saginaw. So you want a 7 bolt side cover 3 speed. These are fairly common. And interchange with the big gm cars.

Got one in my current truck, a '65 3/4 ton. You will want 4.57 gears because the first gear of the 3-speed is too high. Not sure how it would work with 4.10 gears for taking off, but in overdrive it is a 30% drop in rpm's. It turns those 4.57's into 3.19's in overdrive. So the rear-end gearing is also something to be aware of.

Loweboy. There are 4 different first gear ratios if you have the Saginaw swapped in. Could not get a factory 3/4 ton with the OD. You would want the 3.50 first. You may have the 2.54 or 2.84.