The Stovebolt Site Forums The Shop Area Driveline GM Saginaw 4 speed

Patrick's antique parts shows an adaptor for the gm Saginaw cast iron 4 speed for the torque tube trucks.

I have a 48 3100 with the torque tube and would like to hear if anyone has used this.

How do I identify this transmission?
How much are they worth?
Is this a good option instead of the 3:55 gears?
What else is needed for this conversion?
Any other information is welcomed.

Thanks

This is the only part I can answer for you; Basically, the answer would be no. The Saginaw 4 speed still has a 1:1 final gear, same as the 3 and 4 speed original transmissions. The advantage is the that the gear ratios are closer together, which makes for better drivability. But for improved road speeds/lower rpm at a given speed, the only thing that would help that is either a higher gear set (lower numerically) or an overdrive transmission. That said, the Saginaw conversion is really meant to compliment the 3.55 gear set, rather than an either/or situation.

Thank you

Now to find the best price on the 3:55 gears. I am sure this topic has been spoken on many times but any suggestions or advice?

Thanks again

apparently the best price is from mothertrucker in AZ, but note that you'll also need the 'installation kit' [bearings and such], which I don't think he can supply

Bill

I've used the Saginaw 4 speed and it's fine but better set up and possibly much less money would be the T-5. Has an overdrive gear, you don't need to buy a shifter and being a top loader it's centered in the floor. Need to lose the torque tube and go to more modern driveshaft and replace or modify the rear end.

Lots of how-to articles on the T-5 swap.

Two birds with one stone: Get the Saginaw and dump the tube and rear end. Get a 3.08 or 3.42 for hiway or the perfect all around ratio: 3.73. No adaptor needed. 4 speed Saginaw has three shift levers and ID from the web. There are several ratios of them , identified by the grooves on the input shaft. Price varies. $150-$400 , get the shifter with it if you can. There is one on San Diego/OC craigslist now for $200. And one in L.A. with clutch, bell housing, fly wheel, Hurst shifter and the trans is rebuilt for $600.(3 groove)...Hesperia with Bell housing $180 (3 groove). They have shaft size and spline count differences, I think, so be real sure it fits your setup before you buy. Also check clearance to truck bench seat. Buckets? No problem.

Saginaw 4-speed 1st 2nd 3rd 4th (according to the web)
No grooves 2.84 2.01 1.35 1.00
1 groove 2.54 1.80 1.44 1.00
2 grooves 3.11 2.20 1.47 1.00
3 grooves 3.50 2.47 1.65 1.00

Thank you