Going to a 3:00 or 3.25 gear should improve your speedometer accuracy unless it goes too far the other way. Without doing the math (which I have no idea how to do) I'd guess that the 3:00 gear will make your speedometer closer and a 3:25 might make it a little slow. Remember that each tooth on the speedometer gear is worth about 4-5 MPH, so after you change the rear gears and you find that it's still off you will have to replace the speedometer gear.

Vern

 

To change the speedometer you will have to change the gear on the end of the speedo cable on the end that goes into the transmission. It is easy to do and involves just pulling the cable from the tranny. Your Ford dealer and maybe some parts stores should have a different count gear to attach to the cable. Use GreatNorthWoods suggestion for the gear count to get one that will be correct.

 

That was the best part of when I changed my rear ratio. My speedometer used to read about 8 mph fast and now it's almost perfect without having to change speedometer gears .

 

06

7.00x15 Light Truck Tires.
No, you are only Partially correct.
That is the Size that IS listed In Relief as Cast On the Sidewall of the Tire.
And that IS also One of the Tire Sizes Listed in my Original Owners Manual.
I Do Not use the New Style of Bleedin' Rediculous tires on my '58 M-100 fore my Original Rims were Not designed to Use these Short Wide Excuse for Tires they sell these days, Plus I Just Do Not Like them.

 

Here's a Formula for figuring out the correct gear.

(T*G*20.2)/D = Gear needed

T = Gear on tranny tailshaft normally 8 or 7 tooth
G = Gear Ratio
D = Tire diameter

(7*3*20.2)/26.7 = 15.89
So you need a 16 tooth gear for 3.00:1

(7*3.25*20.2)/26.7 = 17.21
So you need a 17 tooth gear for 3.25:1

 

i think the link is broken,,,i will keep trying so i gont have to get my fat self up til i need another brew,,,lol

 

What trans, and tire size are you running with the 3.25s

 

Its depends on what your daily drive is. Mine is 38 miles each way of open road both interstate and back woods. I had a 302 with a C4 and 2.73s in the back. Highway speed 70, back woods speed 60, average mpg 17.3. Plenty of zip for me, but I am easy to impress I have never had much power.

Truck was reworked for the last 9 months and we brought the 302 up to 315hp and added an AOD plus kept the 2:73. The goal was for highway speed (70) and mpg of 20. Test flight begin in May.

Jet Jock
"I drive a 'girly' 302 because, when I want to go fast, I go to work"

 

I'm running the stock 3 speed with 235/75R15 tires. I think it's the best compromise between acceleration and cruising for a stock flathead. With more power you could obviously go a lower ratio but it all depends what you want, low rpm cruising or acceleration.