Originally Posted By: panic
If you do the math, you'll find that (unlike a purpose-built truck auxiliary transmission) you have a theoretical total of 8 ratios, but some are so close together as to be useless.
Example, using .70 OD:
1st 2.84
1st OD 2.00
2nd 2.01
2nd OD 1.41
3rd 1.35
3rd OD .95
4th 1.00
4th OD .70
Look how close 1st OD is to 2nd, 2nd OD to 3rd, 3rd OD to 4th: they don't do anything.

Using a close-ratio box:
1st 2.56
1st OD 1.79
2nd 1.81
2nd OD 1.27
3rd 1.37
3rd OD .96
4th 1.00
4th OD .70

Still nothing...


Dang, I've been torturing myself over finding a 4 speed Sag to marry in my '69 3 speed + overdrive. All that torture is laid to rest with a beautiful numbers chart! Thank you. I really should have known better from all my triple chainwheel touring bicycle experience (lots of nearly identical crossover gearing). Thanks so much.

BTW, I'm a daily driver only vehicle. The '62 3 sp+ od is the one Jack Halton sold to me in '98 at Latimore, PA. I do split the gears and have 6 forward gears, 2nd overdrive is a fantastic gear for my '57 3.90 rear.

'49 Chevy 1/2 ton, '56 235, 848 head, Fentons, x-pipe, 1-2bbl H-W.