3 speed Saginaw behind a 454!

[73kay]

I've never seen it done, but it exists! https://tulsa.craigslist.org/cto/5581259688.html

I don't know how it is surviving behind that big block. Hahah

[Dc42d76]

Those 3 speed saginaws are bulletproof. Hold up to 600 + horsepower in the Racecars . Only thing that happens is the ears where they bolt to the bell housing crack eventually.

[73kay]

Ya I have not been too kind to my Saginaw behind my 350 but I guess it's how you drive it.

[D13]

There are two different Saginaw 3 speeds in our era. The one in my 3/4 ton is stronger than the ones in my 1/2 tones, including beefier shift rods, etc.
The key, like any manual trans, is to not shock load it. Let the tires spin a little, let the clutch slip a little, and they will be fine. Bazillion ft-lb of torque, suddenly applied, will break most things, hopefully the sacrificial u-joints first.

[73kay]

Originally Posted by D13

There are two different Saginaw 3 speeds in our era. The one in my 3/4 ton is stronger than the ones in my 1/2 tones, including beefier shift rods, etc.
The key, like any manual trans, is to not shock load it. Let the tires spin a little, let the clutch slip a little, and they will be fine. Bazillion ft-lb of torque, suddenly applied, will break most things, hopefully the sacrificial u-joints first.

Really? Huh didn't know that. I have two mid 70s 7 bolt side cover sags that were always mated to a 250

[lyrikz]

Originally Posted by 73kay

I've never seen it done, but it exists! https://tulsa.craigslist.org/cto/5581259688.html

I don't know how it is surviving behind that big block. Hahah

My blazer has that combo. 454 with a 3 speed. Worked fine.. To slow on shifting for me so i took it out.

[Keith Seymore]

Originally Posted by lyrikz

My blazer has that combo. 454 with a 3 speed. Worked fine.. To slow on shifting for me so i took it out.

Passenger car type three speed?

Or the SM465 three speed with the creeper low?

K

[lyrikz]

Originally Posted by Keith Seymore

Passenger car type three speed?

Or the SM465 three speed with the creeper low?

K

Sm465 3 speed with creeper low. Its about ready to be in scrap as we speak. Are they worth anything?

[68Timber]

Originally Posted by lyrikz

Sm465 3 speed with creeper low. Its about ready to be in scrap as we speak. Are they worth anything?

Yes, it's considered one of the most bullet-proof trans ever made. Jeep guys and rock crawlers love them although the NV4500 has taken some of the attention away.

[lyrikz]

Originally Posted by 68Timber

Yes, it's considered one of the most bullet-proof trans ever made. Jeep guys and rock crawlers love them although the NV4500 has taken some of the attention away.

So i should put it up for sale instead of throwing it away? Any idea what i should ask? If i sell it, i will split it with you. Seriously.

[68Timber]

Dude I appreciate that but I wouldn't think of it, besides - you're going to deal with some CL wackos before you find a buyer. I don't know about your market but I see them for sale in the Atlanta area listed from $150 to 175, and that's usually for one that's already been pulled and is laying on the ground. You're in a spot where a potential buyer could test the trans out before you pull it so they know they're getting a good one so $250 or more is a reasonable starting point.

[MikeB]

Here are the 1st gear ratios that I found for Saginaw 3-speeds used in the early-mid 1980s. I did the search last year to see if it would be a good idea to use one that came behind a 250 six for my new 350 V-8. Obviously it would have been a bad idea! The taller the ratio (lower number), the more torque the trans can handle. Never could find the torque-handling specs, though.

3.50: 250 six
3.11: 292 six
2.85: 305 V-8
2.54: 350 V-8

I guess if you drive conservatively and don't pull a trailer, you could get away using one designed for a 305 or 292. But I wouldn't do it.

I couldn't find one that was used behind a big block, but I'm pretty sure trucks were available with that combo, at least in the mid-late 60s.

****Edit**** Just found this info for 1966 vehicles. It was Borg Warner trans that was used behind a 396.
B-W H.D. 3-speed Manual (327/396) 2.41 1.57 1.00

Maybe Keith Seymour can shed some more light on the subject.

[MikeB]

Unless I'm doing the math wrong, it looks like a Saginaw trans with 2.54 1st gear can handle 38% more torque than one with a 3.50 first gear. Of course that assumes the same case, spline count, bearings etc. with a different gearset.

Similarly, an M21 Muncie 4-speed with a 2.20 1st gear can handle 15.5% more torque than an M20 with 2.54 1st gear. The M22 took it a step further with straighter cut gears (for less side-loading) and more splines on input and output shafts.

[Keith Seymore]

I'm not quite sure what to add, so I'll just "free express" a little bit:

As a customer you would would specify the three speed column shifted manual trans (merchandised option MM3) on the order blank.

There were two different versions of that which the engineering release would choose from, (non-merchandised options M62 or M64), with different first gear ratios selected based on other vehicle criteria (engine, series, GVW, etc).

The fact that the three speed Saginaw (passenger car type) and the four speed Saginaw (passenger car type) were the same external dimensions made swaps a breeze. We used to order our trucks with the column shifted three speed and then immediately replace it with a 3:11 low gear four speed, with a floor mounted Hurst shifter, which was fine for our spirited daily driver/parts chasing/light trailer towing duty cycle.

No big block/passenger car three speed combinations were available from the factory, at least during the timeframe in which I was involved.

I'm attaching the generic info packet for the 1980 pickups, just because it does have some nice additional detail on the SM465/merchandised RPO MM4/non-merchandised RPO M20 (page 112) and passenger car type Saginaw three speeds (page 118), for comparison purposes.

https://www.gmheritagecenter.com/doc...olet-Truck.pdf

K