The Stovebolt Site Forums The Shop Area Driveline Saginaw 3 speed- - - -torque tube?

I'm currently working on a project to adapt a torque tube rear end to work with a Saginaw fully synchronized 3 speed transmission. No, it's not a Chevy rear end, so I won't get into details, but it looks like the same concept could be applied to a stovebolt. Having a 3 speed that doesn't have to come to a full stop to engage 1st. gear, without having to swap an entire driveline might be a good idea for someone who wants to keep most of the torque tube system intact while upgrading the transmission to a somewhat more modern setup. Since the Saginaw 4 speed shares a lot of parts, dimensions, and design features with the 3 speed, that's another possibility that might be worth exploring.
Jerry

Patrick Dykes did this about 25~26 years ago, Jerry. That is to say he had a tail section cast which would replace the 4 speed tail section (as I recall would also have replaced the tail section for the 3 speed but at that time there was more interest in the 4 speed to get the more shallow drop-off in gearing). I have no idea who did this for him, but you could attach the AD torque tube ball right to it. Is this what you're talking about doing?

Yes, but I'm thinking about machining an adapter to attach to the original rear housing, and modifying a U joint to mate the Saginaw output shaft to the torque tune driveshaft. The one I'm working on currently will be used to mate a 1940's Ford banjo housing rear end to the Saginaw 3 speed. There's already a bolt-on front ball pivot that also serves as a rear trans mount for that axle.
www.ebay.com/itm/225834727514

It would be fairly simple to machine a ball pivot to adapt that same casting to a Chevy torque tube ball.
Jerry

Okay...I see what you're thinking. That wouldn't be nearly as much work as Patrick's cast iron piece.

It might be necessary to shorten the torque tube and driveshaft, but that's "metal butchery 101" to any machinist worthy of the name!
Jerry

Making progress- - - - -initial measurements on both torque tube/driveshaft setups look like the project is doable without commissioning anything really exotic beyond what an average-capability machinist can accomplish. The adapter will clamp onto the Saginaw rear housing with 3 setscrews.

Edit: I believe a similar adapter could be fabricated to marry up a T-5 with a torque tube. The length of the torque tube and the internal driveshaft would probably have to be altered to match the length of the T-5 box. That wouldn't be a particularly difficult procedure, just involving some basic machining and welding.
Jerry

There were some T-5 models with a 3.50 first. If you could swap out for a .76 fifth and if you had a 3.55 gear set in the rear, that would be about perfect if you wanted to run it as a real truck and still cruise on the highway at around 2200 rpm at 65 mph. Your overall first gear ratio would be around 12.5. Mine is 12.37. Sounding better all the time, Jerry.

I have a T5 and a Nova rear end with 2.73 gears it will run at any highway speed you want at around 2100 rpm.

Ron, the laws of physics must be "suggestions" where you live!
Jerry

You already know I am mechanically inept. So rather than being obtuse, point out my mistake. I struggled to remember what I had.

Thats not how gears work Ron. You don't get to choose what speed speed you are going for a specific (2100) RPM. I suspect what you meant was that 2100RPM is a good cruising speed, but you can cruise at whatever speed you want. As written it does sound kind of funny.

Out of curiosity, do you know what size tires you are running? A 2.73 is pretty high gearing for most of these trucks and I have been curious how tall your tires were.

Since "overdrive" indicates that the driveshaft is turning faster than the engine, 2100 engine RPM in 5th. gear against a 2.73 rear axle would probably be somewhere in excess of 90 MPH with a normal size tire. Are you sure that axle ratio isn't actually 3.73? I don't think I've ever seen a stovebolt six that would be able to pull a 2.73 gear behind an OD transmission.
Jerry

looking at his gallery information, he has a pacer rear-end in his truck. the standard rear-end ratio was 2:73 for pacers.

Since I don't have a 3 speed torque tube transmission handy at the moment- - - -Is the bellhousing face to the torque tube pivot ball distance the same on a 3 speed and a SM-420? I'm wondering how much, if any, I might need to shorten the torque tube to fit the Saginaw unit once I get the ball pivot built? I've got a couple of torque tube 420s on hand.
Jerry

I have used a torque tube from a 3 speed on my 4 speed truck also have extra ball from a 3 speed and they are the same

If I am not mistaken, they are the same size. Keep in mind that 1947 is different and a single year drivetrain. I will double check the measurements on both 3 and 4 speed 1948+ transmission units tomorrow for you. Rich

Making progress- - - -I just ordered some steel plate to make the female ball pivot to mate to the back end of the Saginaw tailshaft housing. I'm going to build up a hybrid U joint using a Saginaw slip yoke locked into place on the output shaft, and the rear half of an early U joint to fit into the torque tube bushing. I'll do the same type of interface with the Furd torque tube for the banjo housing rear axle on the replica 3 window coupe dirt tracker I'm building.
Jerry