Overdrive kits for Tempest transaxle

I have been planing a build on a Pontiac Torpedo (though I am in no position to build it just yet). One of the modifications I would like to do is to put the transaxle from a first generation Tempest in the back. This would improve weight distribution. As I would have to shorten the axles I figure I could put a pair of universal joints on it providing fully independent suspension, as in the '65 Corvair.

Thing is, the manual transmissions on Tempests where only 3 or 4 speeds, which I do not think is enough. An overdrive kit could double this. I am not entirely sure if the gearbox and axle segments can be separated without screwing up the suspension mounts. Thus I think it might be necessary to put the overdrive unit between the engine and the transaxle. Would this create any problems?

 

I am as big a Pontiac fan as anyone but, I think this is, generally, a bad idea. They have poor susp geometry, hard to find parts, bearings, etc. Plus, they are weak and more.
For sure, if you put enough money and energy into anything you can make it good but, you may wish to choose another direction for a rear end and trans.

Best to you whatever you choose to do.

Steve

 

I am assuming by Pontiac "Torpedo" you mean the fastback 2 doors sedn/coupes of '41 and later. If that is correct, I fully agree with Applekrate on all counts.

However, if you are determined to do this, I don't see why it is necessary to seperate the trans/final drive units. Seems to me you'll have to do something different than the original 'sagging driveshaft' anyway, as it will be too short. So why not place the overdrive unit just ahead of the driveshaft/transaxle connecting point.

Something like a Gear Vendors Overdrive that can be mounted "inline". Further, why not use the far superior Corvair '65/'69 IRS with the Pontiac transaxle? All of this requires A LOT of facbrication, with dubious outcome......but I'm just offering suggestions in case you can't be persuaded otherwise.

Basically, as Applekrate indicated, you are pairing components from two completely different categories (weight/size) of vehicles. If you are open to re-thinking this, consider using either Jaguar or Corvette IRS, either of which is readily available, rugged, reduces unsprung weight, better brakes, etc, etc. The overdrive comes with the 2004R or 700R4 or 4L80 or T-5 etc.

Ray

 

I want everything on the car to be either taken from a Pontiac car or new build. And yes, I do know that a Tempest transaxle is just a slightly modified Corvair transaxle. I am fully aware that these modifications will take a great deal of time, effort and money. If I wanted something cheap, quick and easy I would get a Mini Cooper.

Mr. Applekrate said the tranaxles from a Tempest are "weak." Could you please clarify this? I understand that the torque converters on the automatics tend to balloon and burst with relatively little power. Would the manual transaxle be capable of handling a ~300 HP engine.

 

While I applaud your attempt to keep it all-Pontiac, think about the configuration of the Tempest transaxle. Any OD unit would need to go between the trans output shaft and the differential gears. That's pretty tough to do in the stock configuration. While this violates your self-imposed requirement, consider a C5 Corvette transaxle. It uses a T56 or 4L60E as the basis for the trans.

 

The OD unit could be located behind the engine and ahead of the transaxle unit.........it can be anywhere between the engine and the wheels to be effective.

Ray

 

The trans was basically a standard Saginaw unit. If there is an overdrive version of that trans maybe it could be used?

While I no longer remember the particulars, the '63 transaxle was stronger than the '61 - '62.

For a heavy car, with 300HP, that is driven hard, the transaxle would be a weak link. In a light car and/or driven normally the transaxle would be adequate but not overbuilt.

Since you would need to do something about the solid driveshaft anyway, replace it with a "regular" driveshaft and a custom trans input shaft. That has been done before. Because the driveshaft is on the input side of the trans it doesn't need to be as big/heavy as a "regular" driveshaft.

I know you want to keep this all Pontiac, but there are a number of alternatives out there that would be a better option(and in the end cheaper) than the Tempest. I've never understood the idea that it's ok to mix and match parts that were made 50 years apart so long as they were made by the same manufacturer, but not ok to use an equally unrelated part made by a different manufacturer. I know that's another discussion, that some are just hung up on the concept, and that it's your car, so do as you wish.