I think the lowest Dana gear was 3.54, because I've read before about the need to change stuff between gear sizes, one size works to 3.73 or 4.10 and the other size for on up to the 5's check for a vertical tag on the readend facing the back of the truck it will be between two of the bolts holding the back cover on, it'll list the gear ratio.

 

I span the tires to check the ratio,it takes 2 turns of the
shaft to 1 tire revolution but the thing is ltd slip so
that would make it a 4.10:1 right. if it is what
ratio could i raise it to without loosing that much
low end power.







Fe power

 

Did you turn the driveshaft and watch the tire or turn the tire and watch count the driveshaft turns?
It make a difference !

Dennis https://www.ford-trucks.com/user_gallery/sizeimage.php?&photoid=1733&.jpg



Please Don't Ask Me Any Tough Questions,
"I'm Saving My Memory For When I Develop Alzheimer's"


78 F-150 429CJ,Silver, Explorer Pkg.
641/2-Mustang 260,Pre-World's Fair Car.
64-Fairlane500 S/C waiting for a 390-4spd.
68-Mustang 289-Sunlit Gold 80,892Mi
78-Buick LeSabre 403 4V
84 Volvo DL Wagon

 

Oops. I missed that comment about the "redline" being on the speedo. Of course that doesn't make any sense.

To determine your actual axle ratio, you need to either do the driveshaft/wheel turn-and-count test, or get a tach. Using your speed while in 4th gear at a given rpm, you can determine what your final drive ratio is through some fairly simple math. Your tires are 31 inches tall, which means they are roughly 97.4 inches in circumference. Thus, your truck travels 97.4" forward every time the axle completes one revolution. In 4th gear, your transmission ratio is 1:1, so we can disregard it for now. If your final drive ratio is 3.50:1, that means that the axles rotate once for every 3.5 turns of the driveshaft. At an engine rpm of 1000, then, while in 4th gear your axles will be turning 1000/3.50=285.7 times per minute. Each of those 285.7 revolutions of the axle moves you forward 97.4 inches, for a total movement of 27,829 inches. Divide by 1,056 to convert inches per minute to miles per hour. The result is 25.8. This means that a truck with 31" tires and a 3.50 rear axle ration will go 26 miles per hour for every 1000 rpm while in 4th gear. At 2000 rpm, it will be traveling at 52 mph, and at 3000 rpm it will be traveling at 78 mph.

If you have a 4.10:1 final drive ratio, the same math shows that your truck (on 31" tires) will be traveling at 22.5 mph for every 1000 rpm (45 mph at 2000, 67.5 mph at 3000).

It also means that if you have 4.10:1 rear end gears, and switch to 3.50:1 gears, you will see a drop of 13% in rpm for any speed. Instead of turning 3100 rpm to go 70 mph, you'll only need to turn 2700 rpm.

 

Since somebody already mentioned it, just what the heck is that redline on the speedometer? They appeared in ’68 and I have seen them on F250s and 1 ton Econolines along with a lot of cars too. Thought it had something to do with the national speed limit but what about the F100s and lighter-duty Econolines?

Barry

 

I've seen them on 67 and 68 F100's

 

That’s interesting TP, now the waters are really muddied up. So some F100s had it and some didn’t, looks like another Ford enigma like the hazard switch. Sorry for going off-topic but it's never been mentioned before. '67 eh?

Barry

 

I have a 1967 ford f-250 with the red line so i know it was atleast started in 67.It kinda looks like the speedometor is broken off and layin down