jpolk34

I recently ordered a 2010 F150 Supercrew 4x4 with the 3.31 gear ratio for the best fuel mileage, but in that ratio a limited slip is not available, so I was going to install an aftermarket limited slip in it. Does anyone know what rearend they are putting in the 2010 F150's? Is it the Ford 9.75? Thanks.

1sweet09fx4

Hope your going for highway miles, cause in the city thats gonna be a slug. IMO

Lenn

x2.

SCScrew

jpolk34,
I will have to agree with the other posters. A 4x4 supercrew with 3.31 gears is going to be slow off the line. I have a supercrew 4x4 with the 3.73 gears and I would get a 4.10 if they offered it from the factory as I like to have all the gear that I can get. My wife has an 08 Expedition that has the same 5.4 engine and 6 speed trans that our trucks have and it has the 3.31 gears. It is only a 2 wheel drive and we do not tow with it so it has not really been an issue but I would not think of towing anything with that rearend. In the mountains and on hills around town, it is always downshifting looking for more power.

In regards to mileage, I would venture to say that there probably is not more than 1 MPG difference between a 3.31 and a 3.55 and maybe only 1.5-2 MPG between a 3.31 and a 3.73 but the acceleration and power will be very noticeable. I was getting around 15-15.5 MPG after putting about 10K miles on the truck but I have just installed custom tunes from Justin at VMP Tuning and am now getting 18-18.5 MPG on the freeway with his 89 octane mileage tune.

If it's not too late, you would be better off changing your order to include a 3.55 LS differential. That will be much cheaper than changing out the rearend on a new truck and you will be picking up some extra power as well. If it is too late, see if your dealer will find you a truck like you want on another dealers lot that already has the 3.55 LS diff (if they don't have what you want on their lot) and they can put your truck on the lot to sell once it comes in. I can't imagine them not doing that.

These are just my thoughts but I think you will be disappointed in the 3.31. These trucks get better fuel mileage than the previous F150s so there is no need to skimp on the gears to try and save a few MPGs.

flareside93

everything SCScrew said was correct.
For best performance, get a tune and 4.10 gears in both axles.
cause remember, if its 4x4 you have to regear BOTH axles.

justice1736

iTrader: (1)

i have an 09 scab with the 3.31 gears and 5.4. it tows my boat just fine. i get round 20-21 mpg on the highway with 100% gas. and 19 with the gas that contains up to 10% ethanol. yeah my dads screw witht the 3.73 tows better but his mpg sucks compared to mine. and around town its not too bad. yeah its a little slower but i dont really hot rod off the line.

miztigerszou52

To answer your original question...it is a Ford 9.75 rear end. You can look at Eaton, Auburn or Detroit for a 3.31 limited slip rear.

thump

Considering a Detroit will cost you $460 plus labor you do realize it will take a loooooong time for you to ever make up the cost of adding aftermarket LS through the 1 mpg you'll save vs ordering 3.55/3.73s... And as other have mentioned, you'll likely get worse mileage in city traffic.

jpolk34

Thanks for all the info guys, I'm gonna stick with the 3.31 gears though(got a Jeep with 4.88's and lockers for the four-wheelin) because more than likely the only offroading this truck will see is when I go hunting and thats mostly gravel roads. I imagine the 3.73's would be more powerful off the line, but I don't plan to do any hotrodding in this truck. It will mainly be my means of transportation to and from work which is about a 60 mile roundtrip on a rural 4-lane highway.

justice1736

iTrader: (1)

ive got about a 90 mile roudn trip on an interstate. so i feel what your saying. i get anywhere from 20 to 21 mpg on the interstate with 100% gas. i really dont notice that much difference between my dads truck and mine. so i think youll be ok. all the 09's are kind of sluggish off the line anyways with that low first gear.