Some questions on OD?

[cam.man67]

Hearing about how straightforward it is to swap in a 3-speed w/ OD into our trucks, I'm considering doing it I do have a couple questions, though:

1. What vehicles did these trannys come in other than trucks, specifically those with synchros on all gears?
2. What is the overdrive ratio, and how much does that drop rpms at, say, 55 given 3.73 gears?
3. With the added OD, what kind of gas mileage can I expect with 3.73 gears and a mostly stock '80s 350? I get about 12mpg right now.
4. What can I expect to pay for one of these in good working order, and should I pay to have it rebuilt?
5. Anybody got a build thread or a how-to to hook up the linkage into the truck?

Thanks in advance!

[SOON2BLAZE]

I'm running a np A833 from a early 80's chevy 3/4 ton. Seems like it is the same length as a th350. It has synchro mesh in all gears and came from the factory with a Hurst shifter al though it is only stamped Hurst on the area where the shift rods mount to the trans at the shifter. I have 3.50 gears with a 27.8 tall tire and turn about 2300 at 75mph. with the BBC and q jet I'm get 10 -14 mpg, as I needs some better flowing heads. I paid 200. of ebay 4 years ago. These guys might have one for you http://www.drivetrain.com/parts_cata...#GeneralMotors if not they sell the parts and rebuild them. They did a great job on mine. hope this helps.

[raycow]

Originally Posted by cam.man67

Hearing about how straightforward it is to swap in a 3-speed w/ OD into our trucks, I'm considering doing it I do have a couple questions, though:

1. What vehicles did these trannys come in other than trucks, specifically those with synchros on all gears?

Chevy passenger cars, full-size and Chevelle, 66-69. OD was not offered in any other GM makes besides Chevy, although I have seen a few that were owner-installed.

2. What is the overdrive ratio, and how much does that drop rpms at, say, 55 given 3.73 gears?

0.70:1. Rpm depends on tire size. If you have stock size tires (approx 27") the rpm will drop from about 2550 to about 1785. With larger tires the rpm will be inversely proportional to diameter.

3. With the added OD, what kind of gas mileage can I expect with 3.73 gears and a mostly stock '80s 350? I get about 12mpg right now.

Don't expect to get rich. In constant speed highway driving you might gain about 2-3 mpg. You won't see any difference in town.

4. What can I expect to pay for one of these in good working order, and should I pay to have it rebuilt?

$200 is a fair price if you can take off the cover and don't find anything bad inside. Make sure the transmission comes with a solenoid and governor and they don't look damaged. These can be expensive to replace if they are missing. Don't rebuild it until you know something is wrong with it.

5. Anybody got a build thread or a how-to to hook up the linkage into the truck?

The transmission is a bolt-in if you are replacing a non-OD Saginaw. If your bellhousing is 68 or later, swap the front bearing retainer off your non-OD 3 speed.

The only "linkage" is a lockout cable. You can use a heavy duty (truck-type) choke or throttle cable if you don't want to pay for the stock cable with a fancy handle that says "overdrive" on it.

All other controls are electrical. The stock relay and throttle switch can be hard to find and pricey if you do find them. Instead, use a toggle switch and a common "cube" relay you can get cheaply from any parts store.

Ray

[cam.man67]

Thanks Ray! That's the OD I was talking about.

Now, based on what you said about the switches and stuff, the stock relay and throttle switch worked in a semi-automatic operation (i.e. if you nail the throttle, you drop out of OD)? The new toggle switch and standard relay would turn it into full manual, correct?

[raycow]

If you want full manual, all you need is the toggle switch and nothing else except a working solenoid.

Using the cube relay in conjuction with the stock governor will give you semi-automatic operation. That is, with the toggle switch "on" the OD will engage if you get above about 30 mph and let up on the gas momentarily. When you drop below about 25 mph it will shift back to direct drive. If you are above 30 mph with the OD engaged, flip the switch "off" and it will downshift to direct if you let up momentarily.

Ray