"40 gear selection

[russcc]

Rebuilding the stock '40 transmission. It will be backing up a 3 5/16" x 4" 59L with 1007B cam, Navarro " Nostalgia" heads, and lighten steel flywheel, (about 26#s).Rear axel is currently a 3:78, running 6'50x16s. I have a set of both 16/28 or 15/29 gear sets. No hills in my area. Any suggestions? Thank you Fordbarners.

[JSeery]

It all depends on what you want to end up with. Run the number and see what appeals to you. There is a link in a recent thread that you can plug the numbers into and see what you will end up with (mph) in each gear.

The final drive ratio is the transmission gear ratio X the rear axle ratio. Good performance street numbers are in the 8.0 to 9.5 range for first gear. Economy range is >8.0 (These are just rule of thumb number by the way)

16/28 1.75 X 3.78 = 6.6 Up in the economy range
15/29 1.93 X 3.78 = 7.3 A little better, but still in the eco range

This is just first gear, of course 3rd is 1:1 so 1.00 X 3.78 = 3.78

Tires come into play here, but this the final drive numbers. Now, where are you wanting to end up? IMO these gears would work better with a lower rear axle ratio, but again that is kinda up to the user.

[JM 35 Sedan]

I've run 4.11, 3.78, and 3.54 rear gears in my '35 fordor sedan, Avatar. I've run all of these rear gear ratios with a stock set 16/28 transmission gears. The car ran well with 4.11 and 3.78, but was bogged down quite a bit when starting off in first gear when I install the 3.54 rear gears. Last month I rebuilt the transmission with a set of 15/29, '46 to '48 gears with the improved synchronized gears, and found this works very well with 3.54 rear gears.

Just put over 1300 miles on this car last week with the 3.54 rear gears and 15/29 transmission gears. This is a really great gear combination for the open road driving. Only a few steep hills along the way required downshift into second gear.

[40 Deluxe]

I would wonder about transmission strength behind that engine! The 15/29 gears would be weaker (due to greater torque multiplication) but I wonder if either one would hold up to "spirited" driving? Seems like a lot of these trannies got shelled out over the years!

[Tinker]

No hills and a strong motor. Run taller gears. Less you stoplight dragging.


.

[russcc]

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Thank you Fordbarners. It looks like the 16/28s will do it unless I switch to 3:54s

[Mart]

I have 3.54s in my truck and run the 15/29 because I might have to haul something. i have 3.54s also in my roadster, with 7.50:16s (taller than your combo) and have the 16:28s in that one. I have a near identical motor to yours in the roadster.

If you watch my recent video you will see the 16:28s work well in a light car.
https://youtu.be/OauMqOHMjq8

I'd only use the 15/29s in a heavier vehicle. They suit my truck well.

Edit: I thought yours was a roadster, In a 40 I'd say your summary is correct.

Mart.

[frnkeore]

Mart,
Great YouTube. The US insurance company's would go nuts if we where able to do that here

Frank

[rotorwrench]

The Mercury cars used the 15/29 sets and they worked well enough and especially behind the new for 1939 99A engine. The 16/28 work well with 3.78s. Is this in a 1940 Ford or something else?

[Seth Swoboda]

Originally Posted by JM 35 Sedan

I've run 4.11, 3.78, and 3.54 rear gears in my '35 fordor sedan, Avatar. I've run all of these rear gear ratios with a stock set 16/28 transmission gears. The car ran well with 4.11 and 3.78, but was bogged down quite a bit when starting off in first gear when I install the 3.54 rear gears. Last month I rebuilt the transmission with a set of 15/29, '46 to '48 gears with the improved synchronized gears, and found this works very well with 3.54 rear gears.

Just put over 1300 miles on this car last week with the 3.54 rear gears and 15/29 transmission gears. This is a really great gear combination for the open road driving. Only a few steep hills along the way required downshift into second gear.

I agree. John's real life experience is accurate and I run the same 15/29 tooth gears with 3.54 rear gears and have experienced excellent results. The amount of touring miles John has accumulated in his '35 fordor is staggering to most.