Three Speed to Saginaw Car Four Speed Swap- Column Shift

[theastronaut]

I'm looking into swapping in a Saginaw four speed from a car (not the truck granny low four speed) into my '66 that has a 250 and three speed on the column. I'm wanting to keep it column shift and add separate cable under the dash for reverse.

What is involved with swapping from the three speed to the four speed? From pics it looks like the four speed has a longer tail shaft, I'm guessing I'll have to shorten the drive shaft? Can the four speed hang from the stock bellhousing or will it need it's own rear crossmember for support? I believe I'll have to lengthen/modify the shift rods, I can weld so that shouldn't be a problem. Anything else to look out for?

The three ring Saginaw ratios from lower powered cars are 3.50, 2.47, 1.65, 1.00 compared to the 3 speed's 2.94, 1.68, 1.00. It currently has a 3.73 R&P. I could swap to 3.08 gears and the overall ratio in first would be the same while dropping about 600 rpm at 75 mph.

[The Rocknrod]

I read where the G Series Van had a 4speed column shifter with T10 4 speed. I think it was only in 2nd Gen, G Series '67 - '70.

[theastronaut]

Yep, vans, some Ford cars, Japanese trucks/vans had five speed column shift. I'm fairly certain the stock column will work, just have to modify the shift rods to fit the new trans.

[The Rocknrod]

Someone has done it - https://www.chevytalk.org/fusionbb/s...hp?tid/265107/

[AcampoDave]

I like the idea of swapping to a 3.08. I did the math and it looks favorable on "paper".

[theastronaut]

Originally Posted by The Rocknrod

Someone has done it - https://www.chevytalk.org/fusionbb/s...hp?tid/265107/

We had a local guy at our shop years ago that had done the swap and said he used a lever in the floor for reverse. I don't remember him talking about any other details than that, was hoping someone here had done the swap and knew what all was involved.

Originally Posted by AcampoDave

I like the idea of swapping to a 3.08. I did the math and it looks favorable on "paper".

Our shop S10 has a 4.3, close ratio version of the NV3500, and 3.08 gears. The NV's 1-4 ratios are pretty close to the three ring Saginaw. The S10 pulls through the gears effortlessly, although it has a ~30hp, 400 pound, and 3.25" shorter tire advantage over the C10 to help it get up and going. I'll soon be swapping a shaved/lump ported/big valve head and mild cam onto the 250 so that'll perk it up some.

[The Rocknrod]

https://www.67-72chevytrucks.com/vbo...9&postcount=14
https://www.67-72chevytrucks.com/vbo...8&postcount=30
More off site info - https://vintage-vans.forumotion.com/...-speed-linkage

[AcampoDave]

I ran a 3 ring Saginaw for years with a 2.76 rear and 235/75/15 tires. The gears were spaced well enough, the starting line ratio was fine too but my 283 just wasn't too happy with the final drive ratio on the 2.76 on anything but flat ground. When I went to a 3.08 rear, with the same tranny, the gears felt short and it was easy to go from 1st to 3rd, or start out in 2nd you know....like driving a 4x4. I ultimately found the 2.76 to be better suited for that tranny and just lived with downshifting to 3rd anytime I needed some oomph outta the motor. With a 2.76, third was good all the way to 75mph anyhow.
My current 4 speed tranny has a 2.98 first and it is really happy with my 3.08 rear end.

Edit: I wonder if your current 3 speed would play well with a 3.08. My longbed has a Muncie long tailshaft 3 speed and 225/75/15's and its stock 233 is sweet with a 3.08

[theastronaut]

Thanks for the insight, sounds like 3.08 is the sweet spot with a smaller engine. I like shorter gearing, I've always had small cars (VW bugs, Ford Festivas) that have short/close gearing and it makes them more fun to drive around town. The wide spacing of the three speed isn't as fun, and taking off in second from slow speeds is pretty sluggish from the wide spacing, although the current engine isn't running at 100%.

I plan on doing some occasional lighter duty towing (1300# aluminum trailer, 1700# car) with the truck so I thought the 3.50 first gear would be better for that. The 250 has a bad head so it'll soon be swapped out for a lump port/big valve/shaved/ported head and mild cam, and eventually will have an Aussiespeed intake, Sniper efi, header, and small turbo that spools quickly at low rpm. I think 3.08 would be a good balance between taking off in first when towing and lower rpm on the interstate for the amount of power a mild 250 should make.

I had another '66 with a 195hp Chevelle 283, stock three speed, and unknown r&p that could cruise at 75-80 effortlessly and was still pulling at 95. I'm guessing it had low 3's for r&p gears, I wish I had ID'd them when I had the diff cover off to change the axle seals.