What gears in a stock '48 F1 with 9" rearend?

[Brennan805]

Hello guys. I've searched the forums and had little results finding the gearing that is best suited for my F1. Here's the details...It's a stock '48 with the original 100 hp flatty, 3-speed tranny and dana 41 rearend. Since I can't get gears for the Dana 41, I decided to do a 9" swap (yes, I read the article). I found a nice '64 F-100 rearend that should do a nice, clean bolt up.

My question is; What do you guys suggest for gearing in the 9"?

I intend to keep the original flathead and gearbox. I'm looking for a bit more highway speed at lower RPM's. Basically, a more comfortable ride. Not a lot of hills or grades to worry about, mostly flatland driving. I was thinking 3.50 gears. What do you guys think?

Also, any recommendations or suggestions on the pinion angle? I heard 12 degrees using a 5 degree castor wedge?

Thanks for you time and help.

[Tim Ayers]

Originally Posted by Brennan805

Hello guys. I've searched the forums and had little results finding the gearing that is best suited for my F1. Here's the details...It's a stock '48 with the original 100 hp flatty, 3-speed tranny and dana 41 rearend. Since I can't get gears for the Dana 41, I decided to do a 9" swap (yes, I read the article). I found a nice '64 F-100 rearend that should do a nice, clean bolt up.

My question is; What do you guys suggest for gearing in the 9"?

I intend to keep the original flathead and gearbox. I'm looking for a bit more highway speed at lower RPM's. Basically, a more comfortable ride. Not a lot of hills or grades to worry about, mostly flatland driving. I was thinking 3.50 gears. What do you guys think?

Also, any recommendations or suggestions on the pinion angle? I heard 12 degrees using a 5 degree castor wedge?

Thanks for you time and help.

F1 stock rears had 4:11's I believe and should have a 29 tooth gear cluster in the trans. That 29 tooth will help you get moving from a dead stop and allow you to go with a "better" highway gear on the top end.

How far and fast do you intend to drive it?

Something around 3.25 would make the motor happy on the highway at 65 mph.

[Brennan805]

65 MPH at the most.

It's just an old P/U that needs to keep up with traffic from time to time.

Thanks for the input.

[tubman]

It kind of makes a difference by where you are; mountainous or hilly country vs. the flat plains will make a difference. So will tire size. Also, are you going to use it as a truck a substantial part of the time?

I have 3.55's in my '51 coupe (no overdrive) with 225/75R15 rear tires and it's just fine. 2300 rpm at 55 and 2700 at 70. 2700 rpm's seems to be to be the maximum comfortable speed my engine wants to run for a sustained period of time. In addition, my engine is a little more than stock; a '51 Mercury with prepped Edmunds heads, a 2G carburetor, and a Mallory dual point.

I think the 3.50's may be the best choice. You can fine tune it after using it by going up or down a couple of sizes on the rear tires if you have to.

[cadillac512]

I'd go 3.25 if it were mine, though 3.50 is a good choice as well. As for pinion angle...the pinion shaft should be parallel to the transmission output shaft with the truck at normal ride height. No problem being at different heights....just parallel.

[petehoovie]

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Originally Posted by cadillac512

I'd go 3.25 if it were mine, though 3.50 is a good choice as well. As for pinion angle...the pinion shaft should be parallel to the transmission output shaft with the truck at normal ride height. No problem being at different heights....just parallel.

[tubman]

I have found this video to be very instructive : https://www.youtube.com/watch?v=Idk3BVDVHq4&t=6s

[Ol' Ron]

I couldn't aford a 9". sp I gpt a spicer 44 from a grand cgerokee with 3.73 gers and a posi for 250/ I also fot a T 170 for the same choice. Don't need an adapter for the 8BA steel bellhousing, just make your own/ Gots be the best trans ever made for a Ford truck 65/70 top end and and fantasic pulling power in low . And the Posi in Vermont it\s weight in gold. The only down side is the rear bolt pattern os 5 on 4.5 but the junk yard have millions in them at 15 bucks apiece or less. Now you have a better selection of rear tires.
Sometimes it pay's to be poor.
Gramps

[38 coupe]

Just want to make sure, are you aware that 3.54 gear set is available for the stock Dana 41 axle?
https://www.google.com/search?q=8C+4...t=gws-wiz-serp

[Brian]

I can't really answer your question, however I have owned my car since 1971, done a bunch of miles...I've tried all sorts of gear combinations, I find 3.78 is the best 'all round' ratio; you'll get off the line respectably, and have a good top end. A 3.54 rear is good at highway speeds, but the acceleration will suffer, takes a bit of the fun out of it!

[GB SISSON]

As Tubman mentioned, tire diameter has a lot to do with the equation. There is a formula where you plug in your tire dia and axle ratio and use some fairly simple math and it gives you your rpms at 60 mph in your final drive 1/1 ratio. I know the formula is out there on the WWW. And Ron, I'm gonna look up that transmission right now.

[Brennan805]

Thanks Guy's for all your help. And thanks '38 Coupe for the link. I didn't realize that Dennis Carpenter recently started making Dana 41 gears.

Looks like I just bought a ford 9", Yukon gears and a Master rebuild kit for nothing. Dumbass move on my part..

[Randy in ca]

Here's a good calculator to play around with gears, tire size, etc. and see where it will put you for RPM:

https://purperformance.com/p-29669-rpm-calculator.html

[Bored&Stroked]

I'd go somewhere between 3.54 and 3.78. If you already have the 9", why not use it? The brakes are better, parts are available for a zillion suppliers, etc.. Yeah, you probably have to fab the spring hangers and potentially a new driveshaft, but it is a great rearend!