I have an 82 F-100 with 4spd overdrive and 2.75 ratio 9" rear. I think my gear ratio is too low, but I like the fuel economy of the 2.75. At 50mph, I am only turning the engine at 1200rpm in fourth gear. What other gear ratios would give me good fuel economy, but slightly better performance.

 

Also, what would I need to change the ratio. Just the ring and pinion gear, or the whole center section? Will gears from any 9" rear work in my rear end?

 

WOW!! 2.75 that is high!!
I believe there are 3.05 gears and of course the popular and probably most common 3.55. I have 3.55's behind my 300 and I can get about 16-17 MPG. It also has enough grunt to haul and pull mountains with.

as for what all is required to change the gears..well I will leave that to the experts

 

How do you detrmine the "inch" rearend you have? 8.8 or 9 what have you.



www.classicstepvans.com
Josh Andersen
www.joshandersen.com
1968 Ford P-350 Vanette
Close Coupled

 

[updated:LAST EDITED ON 05-Apr-02 AT 05:46 PM (EST)]I believe it's the diameter of the ring gear. This is a good thread for the driveline forum. Yes you can swap different ratio's between nines, but it's a little more involved that just a bolt on swap. You have to intall the matching pinion as well...check out the tech articles, there's one in there about rebuilding a nine.

 

i have a 81 with 9" rear my dad bought it new in 81 and he special ordered limited slip front and rear with 4.10s he drove it stock tell i got it and modifed the engin but he would get around 15 mpg with everything stock and 4.10s now that i have 33s and a 4brl setup, i get about 10 but hopefully my next one will get atleast 12. just some food for thought i love 4.10s for my tires, expecialy when i put some 35" by 14.5" boggers on!

 

I think the 300-6s with the 4-speeds did the best with the 3.08 gears in it, but that was with a 8.8 rearend. They put the 3.55 gears behind the 5-speeds and some autos. I had a 87 4X4 with a 4-speed (1st= Granny) with 3.08 gears and I could bury the speedo. I do not know if you can put 3.08s in a 9" but 3.05s are close.

 

>How do you detrmine the "inch" rearend you have? 8.8 or 9
>what have you.
>
>
>
>www.classicstepvans.com
>Josh Andersen
>www.joshandersen.com
>1968 Ford P-350 Vanette
>Close Coupled


I believe you can tell by the cover a 9" opens up in the front of the housing and the 8.8" has the cover on the back.(this is what I noticed anyhow) Correct me if I'm wrong.

 

you both are exactly right. the 9" is a rock solid rear end. that is why so many musle cars have them . The 9" has no rear cover that is removeable, it is factory welded on. you remove the whole 3rd member to change stuff ( sux for gear oil change). the 8.8" has a removeable cover in the rear. As far as the ring and pinion, the set for the 9" is actualy 9" and the set for the 8.8" is actualy 8.8". the 9" is just a litle thicker and stronger (actualy lots stronger)