Swapping Pumpkin to 3.31 -- Which one?

3beeps

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I currently have 3.15 gears in my car with 315/50/17 tires (29.4" tall!). I believe swapping to these tires from the 305/45/17 tires I used to use caused my gearing to be too tall, slowing the car down.

I think switching to a 3.31 pumpkin would be the best move to make rather than going back to the smaller tires, so my questions are as follows:
  • Are there different 3.31 pumpkins? Is one better than another?
  • What must be done to get the speedometer to adjust properly for the change?
  • Are there any other pieces to this swap?
Thanks for any help!

 

SolarFlare

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Manual iron 3.31 diff is what you'd want, I dont think any came in aluminum since 3.31 is a manual gear. It will come with a manual flange, which you'll have to swap out for the one in your current diff. As far as speedo, I dont think you'll have to, I think the car looks at wheel speed and OSS to correct but could be wrong. You wont need anything else.
 

Momogt26

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Speedometer should correct it's self. 3.31 and 3c converter are my next mods
 
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3beeps

3beeps

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Hmm my speedo reads low by about 5-6 mph right now because of the monster tall tires.

Does that mean after I change the rear gear ratio, it will still read the same 5-6 mph low?

If so, is there a way a Ford computer could recalibrate it?
 

 
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