What final drives are available for the f150 from the factory? Is 3.55 the lowest? Can you get the lowest on all trim levels? Do any aftermarket companies make any final drives lower than this?

This is a concern for a truck that will spend most of it's time on the highway.

 

The lowest FoMoCo offers is 3.55's you can buy 3.08's from places like http://www.nationaldrivetrain.com/

That's for a 9.75 rear, if you have the 8.8 you can get 2.73's, 3.08's, 3.27's

 

you may want to do some research on whether or not 3.08's will really save you any money at all. i mean these trucks are heavy and getting going from a stop with 3.08's might cost as much gas as you are saving on the highway, not to mention the cost to replace the gears. you will also lose acceleration, which apparently is not your concern, but sucks none the less

i may be wrong, but its just something to keep in mind

 

If anybody knows about acceleration Smok][n', it would be you.

 

i know lol, and im one to talk about "good gas mileage" i get like 4...

 

That's awesome!

 

Here are the gear ratios I've found on 04 and 05 models:

(8.8-Inch Ring Gear/3.31 ratio) (1997-2005 F-150)
(8.8-Inch Ring Gear/3.55 ratio) (1997-2005 F-150, 2002-2005 Explorer/Mountaineer/Aviator)
(8.8-Inch Ring Gear/3.73 ratio) (1997-2005 F-150, 2002-2005 Explorer/Mountaineer/Aviator, 2003-2004 Expedition/Navigator)
(9.75-Inch Ring Gear/3.31 ratio) (1997-2005 F-150, 2005 Expedition/Navigator, 1997-2002 Expedition/Navigator)
(9.75-Inch Ring Gear/3.55 ratio) (1997-2005 F-150, 1997-2002 Expedition/Navigator)
(9.75-Inch Ring Gear/3.73 ratio) (1997-2005 F-150, 1997-2005 Expedition/Navigator)

So it looks like 3.31 is the lowest Ford offers, and IMO is better than 3.08 as it provides similar ratios to a 3.08 and acceptable power.

 

2008 axle ratios from towing guide:

Superduty 3.73 4.10 4.30 4.88 5.38
F-150 3.31 3.55 3.73 4.10
Expedition 3.31 3.73

 

Nice. Anyone know if the 4.10 from Ford is a good purchase? My dealer is more than happy to do the swap but I was wondering if there are better sets out there for the price.

 

Ford gearsets are pretty good, considering they're chosen based on their ability to handle towing and hauling. You can find a better price but I doubt you'll find better quality.

 

ecof150,

Just my personal opinion, if you are serious about changing to 3.08's as most of your driving in highway why not go with and overdrive unit. With the cost of gears, labor for installation and such, just spend a little bit more for an overdrive unit and have the best of both worlds. If you have 3.55's now you could drive around town in 3.55 final, then hit the overdrive unit on the highway. On the automatic overdrive transmission and 3.55 axle ratio and 0.71 overdrive your final drive ratio is 2.52 to 1 and when you kick in your overdrive unit it reduces it to a 1.97 to 1 final drive ratio. Something to think about.......

 

My 08 came with 4.10 limited slip. Limited slip is optional an all 08 ratios except for the 3.31

 

Swapping gears for fuel economy is just not going to pay off. Its like buying a hybrid. By the time you come close to recoup your money, chances are you'll have something else.

I have 3.55's and factory 18s. My rpm at 75 is right at 2000. These things are not turbodiesels, gearing them is not going to make that much difference.

Food for thought. A 3.55 gear is a tall gear, where a 4.56 is a low or short gear. If you say you want to go to a lower gear, then go 4.10's. Final drive ratio is just that, its not the rear end ratio. Final drive ratio (as mentioned) is the OD in the tranny x's the gear in the rear diff.

A cheaper way to lower your rpm's is to slow down. 65 with a 3.55 and a tall tire will get you some better mileage. Also a taller tire will lower your drive RPM's by quite a bit. At some point, the efficiency wears off because you'll have more unsprung weight and a higher rotating mass.

BTW my truck gets 17.8 on the hwy and about 11 stop and go on rural hwys. I think I could get better OVERALL mileage if I had some 4.10's. These pigs are heavy and it takes some grunt to get my pig moving.

 

very true. Now as for overdrive units, I'm guessing it's a box you would add after the transmission and install a shorter driveshaft?

 

Correct Josiah, if it is 2wd, then you replace the tailshaft housing with the OverDrive unit and it is electronic controlled gear splitter. If it is a 4wd then the OverDrive unit is on the transfer case. I have had one on a past truck. Very simple to install, once you have the driveshaft shortened. The one we had was actually an underdrive unit, but works exactly the same.