I have been hunting axles/gears that are more road friendly than 3.92s. I put 3.33s in my 52 with the 215 6 and was very satisfied, I am also running radials on 15s. Now, the 51 I am building will have a 239 flattie 4 speed t98, and 16 inch rims. I found a scout rear end that is a dana 44 that was the correct width, and correct bolt pattern. It has 3.07s. This scares me a little because I am pretty sure that flathead will not like it. With the 4 speed I think startability will not be an issue, but acceleration might be. I could put smaller tires on it to try and accommodate. I did some calculations with the 3.07 and 6.00-16s. 40mph@1500rpm, and 70mph@2581rpm. What do you guys think?

 

That's not bad, but you are right in thinking about starting out. Do you want to have to use granny low to get moving? What is RPM per mph in 2nd?

That's interesting about the Scout rear end; what year was it out of? Did you have to relocate the spring perches? Is the yoke same as ours? I'd rather deal with perches than change driveshafts.

 

Well i am not sure what year of scout that it is out of, but I think i was wrong about the width. It looks too wide in the picture, but I dont care as long as i can drop those gears in my axle. Also I could not find the ratios on the 4 speed but the ratios on the 3 speed are 1st 2.78 2nd 1.62 3rd 1 reverse 3.63. This is the trans that my 52 has and it gets along great with the 3.33s.

 

Not clear that you can drop the gears from the Scout into the F-1. Read here:

https://www.ford-trucks.com/forums/7...hangeable.html

Check the spline count on the axles, that determines if you can use the spider gears from the scout. I'd like to see this work but it seems to be a problem. You need to use the Scout carrier. Bearing diameters need to match, but don't always. Try it and let us know!

 

Well I would drop the whole carrier in it, and i am pretty sure it will go in, and if the spider gears are different splines then i will switch them or have the axles cut and resplined.

 

The ratios for a T98 are: 6.4, 3.09, 1.69, and 1. Granny is still too low, You probably would do (a little) better with the wider ratio heavy three transmission.

 

geez that is low, but I am going to use it anyway!! I spent a long time looking for that trans, then sweat and swearing putting it in!! I think the 307s might be fine then.

 

1st gear w/28" tires: 3,000 RPM = 15 mph

2nd gear: 3,000 RPM = 26 mph

3rd gear: 3,000 RPM = 48 mph

4th gear: 3,000 RPM = 81 mph

It's not that bad, but first is awful low, and I still wonder if the flatty can pull 4th on any kind of hill.

 

My first F-1 was all stock with a 4 speed, flatty V8, and tall skinny 16" tires. I swapped in a 9" with 3.25 gears and it drove really nice. 65 on the highway, good response too. Man I wish I had that truck still.
My current truck has a flat V8, 3 speed and 3.00 gears....I'm hoping they are not too tall. Just waiting for spring to find out.......

 

My rear gear is a 4:10 and that is just too much. I plan to drop to something in the 3:23 or so range for better drivability and mileage. Of course you do give up the ability to spin those big meats at will...

jim

 

With the transmission that I am using plus the IRS and the tires I will be running, I calculated that at 75mph I will be turning 2,008 rpm's. Good gas mileage and the lower gears when I need them.

Transmission - T5z - 5th gear = .73
Differental - Lincoln - 3.07 gears

___________________________________________
46 Ford Street Rod
48 Ford F1 - Custom


"Automatics are for washing machines"

 

Just a thought, not knowing what engine you have but what I have been able to research is that the highway rpm at 70 should be around 2500. The reason for this is most motors are in their torque range and can pull the gear easily. When you start getting lower it is below the torque and the motor will use more gas when trying to pull the gear.

Not saying yours is wrong or anything like that, just some reference material I came across. Just food for thought.

jim

 

I think that will work out, I can throw it into granny on an incline if I need to just to get rolling and go from there, next is trying to get my hands on those gears.

 

You shouldnt have any trouble pulling the 3.00 gears. a friend swapped a T5 with the.68 overdrive in his 53 flatty. he has 3.92 gears, with the overdrive 5th it is about the same as 2.66 gears. that flatty has no problem running at above the posted speed on the highway. we do have alot of flat land in Texas.

 

For those with a rpm calculator, what rpm would I be at 70 mph if I have 28 inch tall tires and a 3:23 rear gear? Hmmm maybe that should be 65 as that is the speed limit......

thanks
jim