Gear Ratio's

[69Ford]

The gears in my ford 9" were changed years ago. I have the original gears. I believe They were changed by my dad for a lower gear for towing a fifth wheel trailer. 3:25 were original according to the vin. And thats what I have on the shelf. In the truck I have 3:50's. Know I not much up on gears is the 3:50 a lower gear. And how much does that put my speedometer off. Thinking about going back to original for gas milage. Also put a F500 speedometer in the truck will this make
a difference in the speedometer reading. Any help

[Donnie]

The change is minimal I.E. 3:50 to 3:25.......is hardly worth while.....if you don't intend to pull a load or off road it & are looking for mileage, why not consider a higher gear set...? You could accomplish this much gain with larger tires... Not sure about the 500 speedo question............Donnie

[69Ford]

I.m going back to the original gear 3:25 Took the rear end apart last night "first time ever doing this" But hey I'm willing to learn wasn't so bad had a friend help. He has a gauge to chech the backlash. It checked out at 10 thousands of an inck on the gears i'm putting in. If I looked it up correctly .08" to .12" is good. Any thoughts Thanks Friends are awesome.