Please Help identify this Axle / Gear Ratio

[Daringo]

Hey all, I think I have a Ford 7.5 axle with a 4.10 Gear Ratio.

My "little metal tag" reads:

A3890
4SL10 757A15

My truck came with 235/75/15's (which are about 29 inches) . According to the wheel size/gear ratio chart, I gained some MPGs and lost some power when I upgraded to 31 inch tires. I think I need 4.56 gear ratio to get me close to stock performance.

Your thoughts - I am close?

 

[JFA_Spyderman]

Yo,
It looks like you have 4.10 gears. 4.56 might be ideal, but expensive for little gain. Is it an auto or manual? If it's a manual, I would just stay out of 5th gear and you will be fine.

 

[Daringo]

Sadly, Automatic. I guess just keep it in "D" on anything but the highway (then "OD").

Thanks for the reply. I guess the good news is it's not a 3.73

 

[CopyKat]

My "little metal tag" reads:

4SL10 757A15

4L10 is a 4.10:1 ratio with a Limited slip. Not sure what the S represents.

75 designates a 7.5" ring gear.

 

[Original_Ranger84]

Sadly, Automatic. I guess just keep it in "D" on anything but the highway (then "OD").

Thanks for the reply. I guess the good news is it's not a 3.73

Whats wrong with 3.73's? lol that what I run with 31's and I do just fine.

 

[Daringo]

Whats wrong with 3.73's? lol that what I run with 31's and I do just fine.

Nothing I suppose. Just sounds like with that combo it's geared a little more towards low RPMs which improves gas mileage, not power.

As per the Gear Ratio guide:

http://www.therangerstation.com/tech_library/gearandtirechart.html

 

[Bent Bolt]

Whats wrong with 3.73's? lol that what I run with 31's and I do just fine.

Depends on your point of view. I had 4.10's with 31's and auto/2.9L and thought it sucked in high range. Was OK in 4LO.

 

[Hahnsb2]

Nothing I suppose. Just sounds like with that combo it's geared a little more towards low RPMs which improves gas mileage, not power.

It isn't geared toward either with anything other than a 4.0/5 speed...

4.10s with 31s was fine with my 2.9 B2, but with your automatic I'd agree you need 4.56s.