The Stovebolt Site Forums The Shop Area Engine Shop overdrive???

My 64' has 3:73 gears(Ithink) and seems to be wound a litle tight on the interstate. Did Chevy make an overdive that I cold run with my 3 speed? The 230 is brand new and I'd like it to be around for a very long time.

In short, yes, there was an overdrive option. They do pop up quite often. You'll need the later version, an SM326 with the H12 overdrive. There's also some electricals that will need hooked up plus a cable for the lockout, otherwise it's the same as your existing 3 speed and a direct bolt in.
I have one in my '55, it's very enjoyable to drive, turns about 2000 rpm at highway speeds.

Chevy did have 3 sp.overdrive trannies available in the 50s and 60s.I dont know whether or not one of them might work.The other possibility would be to change that rearend to a 3;42,or 3:08,which would help very much at highway speeds and would improve your gas mileage.

If I remember the 64 was the last year of the course spline (10??) output shaft and the 65 went to the fine spline. This would make a 55-64 a direct bolt in. The standard OD rear end was a 4.11 and if you have 3.73 gears then the final drive would be 2.61 in OD which might be a bit shallow for hills or head winds when behind a 230. I sure would give it a try because these units can be found at nearly every swap meet that is of any size and usually around $150. Try to make sure the solenoid is good since if not a good one can run as much as the whole trans cost. In addition to the lockout cable and wiring mentioned you might have to fab up different shift rods unless the shift cover off your old trans will bolt onto the new one or they're already identical--I'm never that lucky.

The O.D. is superior than a higher geared rear in the way that you get to keep your low end grunt for better in-town driveablility or for driving in a hilly area. Just my opinion.

Tramp,

New Process 833 overdrive is the way I recommend you go. It's the easiest, most reliable way to get overdrive in a '64 pickup. It has 3 forward gears with fourth being overdrive. First gear is a little lower than your factory 3 speed, second gear about the same, and third straight drive (1:1 ratio). Fourth gear is overdrive with a .73:1 ratio.

It's the same length as the factory 3 speed (so no driveshaft modifications needed) and, if you can get the original shifter it will require no fiddlng around with the handle to get it to accomodate your bench seat. Plus there are no solenoids you have to worry about wiring up or going bad on you every few years. Only problem you might have is finding a heavy duty bellhousing with a 5 1/4 inch retainer bearing opening because the input bearing housing diameter is 1/2 inch larger than your stock bellhousing. A bellhousing from a truck with an SM465 works perfectly (and they're relatively easy to find in Georgia).

I have one of these transmissions in my 1966 shortbed stepside 1/2 ton truck and it's an enthusiasts' dream come true! My truck has the same rear end gears as yours (3.73) and was turning about 3000 rpms at 60 mph. 65 was my absolute maximum cruising rpms on the interstate, and that was killing my 230. Plus it's not safe to drive on north Georgia's interstates unless your vehicle is able to cruise at 75 mph. At the time that was my top speed.

But now with the overdrive, I've gone from turning 3000 rpms at 60 mph (3200 at 65), to 2600 rpms at 80 mph! Talk about pushing people out of the left hand lane! At the same time I also installed a 292 I built with a mild cam, headers and 4 barrel. There is no lack of low end torque or high speed cruising ability now.

Remember this trans is called the "New Process A833" (also sometimes referred to as GM RPO code MY-6). There are at least two versions of this transmission. One casting has a half-Mopar/half-GM design. You want to avoid that one because it will require the original bellhousing (which is aluminum and doesn't have rear mounting cast into it). The other type is the standard GM 4 ear casting that will working with an old-style large truck, cast-iron bellhousing. Find that one and everything else is an easy bolt-in fit.

-ftyler

The OD transmissions are 22" long, you may find that your 64 3 speed is about 5" shorter which will require a driveshaft modification. Both the early (55-65)and the later (66-69) versions will bolt in. The main differences being the fine spline and the shift arms on the side cover on the later units.
Fred