My 1990 F-150 was originally a manual trans. Well it was converted too an automatic with and AOD as the trans. Im not sure what the factory ratio is on the 4 speed set up. I wanna say its 3.55. well i have 35 inch mud terrains on and it seems that the gears are way too high for this set up. Also i think that the front and rear are two different ratios becaus in 4x4 the front wants too spin faster. I guess what my question is what do yall think i should go too from here i was thinking 4.10. How hard is it too swap the ring and pinion. i have IFS so i cant just get different axles. I suppose i could in the rear but as far as the front end im not sure. And what is i went back to the 4 speed manual? would tat solve my no low end power issue since the 4 speed has lower gearing? Thanks guys!

 

What engine the 5.0? If so go 4.56.

 

X2

 

Requires expensive, special tools, and some know-how. I would leave that to a pro.

Yes you can. The differential unbolts from the axle beam. Find another differential with the gear ratio you want, unbolt your old differential from the axle beam, and bolt the new one on. Done.

 

its getting a 5.8

 

Okay....more to the story. Even with 35s and a stockish 5.8 I would suggest 4.56 gears. Either way you at least need a dial indicator, torque wrenches (inch & foot pound) and access to a press to swap gears. Not impossible but it is an advanced skill swap.

 

Ok. I was thinking 4.56 either way now. its got aluminum heads thats about the only performance done. i am a machinist/fabricator so i am open too all of the tools and stuff that was listed.