Technical 3 Speed Gear Ratios

The 3.50 geared Saginaw is going to be Vega/Monza based. They have "narrower" gears, hence are not as strong. But, for a six cylinder, and probably not being driven by a gear slammer, burnout artist type, should be fine.
I am Butch/56sedandelivery.

 

Rex,
IF you use the formula below, then plug in my current gear ratios of 2:94 first gear and 3:50 rear end ratio, the formula will show that my figures are 10.2:1, which is darn close to the "clutch slipping take off", in his formula.
I do have the need to feather / slip to get it going.
If I use the Saginaw, with 3:50 first gear, and the existing 3:50 rear end, the ratio will be at 12.2 : 1, which fits the guide lines well.
Keeping the present 1959 O.D. with its 2.94 first gear and a 3:89 or 4:11 rear will also get me close to the 12 :1.
There will not be any 70 to 80 MPH for me on the InterState.

Below is a quote fromy 10m Tom Langdons Stovebolt Six, regarding gear ratios and a formula.
Tom has been working with the 6 bangers for a long, long time.

"Gear Ratios
General guidelines would recommend about 12:1 1st gear overall driveline ratio (1st gear x axle ratio) for a good ‘take off’ gearing for a 235 Cu. In. engine. Below 10:1 will require clutch slipping and in excess of 15:1 will be an aggravation similar to a ‘granny gear’.

Final drive should be between 3.0 and 2.50. If overdrive is .73 and your axle is 3.73, your final drive will be 3.73 X .73 = 2.72 (perfect!)!

 

Thanks, no gear slammer here, not anymore, anyhow.

 

Yes, the easiest way would be swapping out the rear chunk, but, from what I see online, the rear chunk may not be the least expensive way.

 

The photo of this trans is, as Butch said, a Corvette 3 speed. The original gearing was 2.20 first gear and 1.31 second gear. This ge****t was also used as an option on p***enger cars. I have one that's dated April of 57 and it has the necked down input shaft, not the replacement full length solid shaft. Since it was considered a heavy duty option it also had that little breather on the tail housing like the Corvette 3 speed.There was a 2.47 first gear ge****t that my buddy who raced a 3 speed in NHRA stock cl***, used because of less drop off from second to third. Second gear was around 1.5. My uncle's 61 Chevy wagon had the 2.47 ge****t, as it was a V8. The 6 cylinders and all early overdrives(through 65) were 2.94 first gears.
The 67 Chevelle mentioned earlier, would have been a Saginaw 3 speed with a small block. There was a Muncie 3 speed that was used in the big block application if the 4 speed wasn't ordered. It was also used in GTO's, and came with a Hurst shifter. I know this because I have one on my shelf.
Someone also mentioned a Saginaw 4 speed with a 2.85 first gear. That was only used in Pontiacs. I had an argument with a noted local transmission shop about the 2.85 Saginaw. He said they didn't exist. He wanted to show me in his books that it didn't exist, but he found it as a Pontiac only.
The early 3 speed mentioned a few posts above would have levers attached to splined shafts with a pinch bolt, until 64, when they went to a bolt down the center of the shaft . The u-bolts were used for aftermarket floor shifters like the Hurst Mistery Shifter.

 

I’m going to add to this old thread and just say the hard part about changing from a Muncie 318 to a Saginaw 3-speed is finding and/or making the correct shift arms (since the two transmissions are entirely different in length).

I’ve done this swap in my ‘67 C10, which started as a Muncie 318. Luckily, for that era C10, the later ones came with Saginaws, so arms are available. For an older vehicle there’d be no factory shift arms available, and they’d have to be made.

PS for C10’s there’s at least 3 maybe 4 different sets of shift arms because V8s and 6s had the engines mounted further back or forward, so there’s arms for V8 Saginaw and I6 Saginaw and V8 Muncie and I6 Muncie.

Sorry to re-open an old thread but this one comes up high on a google search, so I figured it’s the best place to add the info.

Ken

 

Bringing up this post as well after 4 years.
Look for this old Hurst Shifter Installation kit in pictures below, they are still out there, I bought mine as a NOS Hurst Installation Kit a week ago for $75 off of that place that Butch use to mention as his favorite place to buy from lol...
Hurst Installation Kits show there Trans ID Number as 340,341,342 & 344 that have the 4 bolt side cover plates.
My 1963 Chevy C10 Pickup still has its original Muncie SM318 3 speed Trans, low 1st gear is 3.50 with factory 3.73 diff. & I6 changed from 230 to a 250 cid engine from a 74 Pontiac.
People keep looking, Old NOS Hurst Installation Kits are still available, just keep checking as I did each day.

Dustin
(1Nimrod)