66 3 speed transmission with overdrive
 

Does anyone know which years a gm 3 speed transmission with overdrive will fit a 66 gmc pickup. I have a 305e v6 with a 3 speed transmission. The shifter is on the column. I want to put a 3 speed with overdrive and keep the column shifter. Hopefully this will increase gas mileage and speed.

Re: 66 3 speed transmission with overdrive
 

Frost:
Which 3 speed do you have? Does it have 4 bolts on the side cover or 7? The first would be SM318 and the second would be SM326. The Overdrive 3 speeds come in the same variety- 4 bolt side cover and 7 bolt side cover. I would get the same version of the overdrive as your original, if you want the easiest install. The 4 bolt side covers are easier to find in overdrive since they were used from the 50's to mid 60's. The 7 bolt side cover overdrives were only used for a few years from the mid 60's. I have the later version with 7 bolt side cover. It is a great tranny. The main difference with the later model is that they have a synchro first gear. The overdrive parts, particularly the soldenoid and governor are getting a bit hard to find though. Make sure when you buy one to check to ensure these two parts are good. The trannies come up pretty often on Craigslist and Ebay,but they are heavy to ship. I usually use Adhuntr.com and you can search the whole country's Craigslist ads at one time or just a state or region.

Here are some links that may be useful:
http://www.classictruckshop.com/club...5n/rebuild.htm

http://www.classictruckshop.com/club...cts/how_to.htm

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

Hope that helps.
Regards,
Steve
New Orleans

Re: 66 3 speed transmission with overdrive
 

The transmission bolts on with 4 bolts. So an earlier model should work? Thanks so much.

Re: 66 3 speed transmission with overdrive
 

Herm the overdrive guy has lots of parts for the Borg Warner overdrives. Herm is a guru with this stuff.

Re: 66 3 speed transmission with overdrive
 

Do you know if he has one for sale?

Re: 66 3 speed transmission with overdrive
 

Not sure. He is a jeep guy. And that's what his business is serving. But the bw overdrive units were used by most all manufacturers. And most of the parts are the same. Any full size GM car or GM truck from about 55-66 will work.

Re: 66 3 speed transmission with overdrive
 

I can't hurt to contact him. Look up hermtheoverdriveguy.

Re: 66 3 speed transmission with overdrive
 

I just went out and checked the transmission. It bolts on with 4 bolts but it has 7 bolts holding the plate on the side where the shifters are located. I tries looking for a model number but I'm going to have to decrease it first.

Re: 66 3 speed transmission with overdrive
 

Frost:
The bolt count I was giving was for the side cover. If you have 7 bolts, you have an SM326 with synchro first gear. Those are a bit harder to find, but you will see pictures at the links I posted so that you know what you are looking for.

Hope that helps.
Regards,
Steve
New Orleans

Re: 66 3 speed transmission with overdrive
 

Thanks again. If anyone comes across one please let me know.