What would be the best differential gearing in my 9" with stock 3 speed. Im looking for a better all around gear that will allow me to cruise at 70mph and not cause the 292 to scream. My current gears are 3:89 and Im running a 15" tire.

1964 F100 292YBlock

That's tough to say. The absolute best option is an overdrive transmission.

Obviously, any gear numerically lower than 3.89 will be a benefit, but it will take a 2.75 to get your RPM in the 2500 neighborhood. If you do that, forget about acceleration and forget about using it even remotely as a truck.



The good news is that many truck 9" center sections will swap right over, to about 1976, so this doesn't have to be expensive.


Lawrenceville, GA

Here is a formula to help you figure out what Gear Ratio to use for a given RPM, Tire Diameter and MPG.



Gear ratio =rpm x tire diameter/Mph x 336



Example 3000 X 27 divided by 65 X 336... 81000/21840=3.70:1



Hope that helps

"The Master Cylinder"

Enjoying life at the beach in SOCAL

Should have used Charlie's number, to get to 2500 RPM, everything else the same in my example, you need 3.09:1 ratio.



Plug in your own numbers, I don't know how tall your tires are. I'm running 3.55's with a 27" tall tire and it seems be a pretty good compromise for town and highway.

"The Master Cylinder"

Enjoying life at the beach in SOCAL

Salf

If interested I have a 9" pumpkin that is either a 322 or a 291 that I could swap out to you.

I"m looking for steeper gearing for my situation.

My unit is a 31 spline device.

Lemmie know

Oldmics@Yahoo.com

A stock '64 will be 28 spline. Check the axle tag to find out just what you have; it could be a 31 spline by now.


Lawrenceville, GA

I have 6.70X15 tires (27"). Ill look and see what size splines I have, 28 sounds right. And swapping the trans is not an option right now. I will trade anyone who wants to. I was thinking 3.25ish should be good. Better than what I have! Master, 3.55 work good for you? what vehicle are you running them in? The truck is lowered and not used to haul anything. Would a stock 4 speed be ideal? And what would a used 4 speed cost?

1964 F100 292YBlock

I now have a 4.27 rear which I really like. When I'm in overdrive the effective gearing is 3.00. I can now start out in overdrive 1st, but I haven't tried it on a steep hill. I think 3.25 would be better. With the old rear 3.92 and overdrive the effective gearing was 2.43. I couldn't start out in overdrive 1st unless I was pointed downhill.

  Dennis in Lititz PA

I have a 3.10 9" I would swap. I in Asheville, N.C.

-Gary Burnette-

I forgot to add 28 spline.

-Gary Burnette-