My truck is a 00' F150 2wd that has a 3.31 gear in it. I'm wanting to know if a 3.55 LS out of a 00' Expedition will bolt right in or will there be a problem?

 

if they are the same diff yes. 8.8 or 9.75 may be in either depending if its a 4.6 or 5.4. also its not just a simple swap it will need to be set up by someone who knows what they are doing if your speaking just internals.

edit, housing are not interchangeable, you would need to do internals.

 

Both my truck and the Expedition have 5.4's. The only differences are the Ex is a 4wd and has a different suspension setup. At the moment I'm pretty flexible on what it comes out of. Would love to be able to swap rearends, but if I have to settle for swapping internals that will be fine also. Won't be the first time I've done this. Main things I'm after are a better towing gear and retaining most of my mpg. The Ex in question has an H9 axle code which is a 3.55LS. As I said before I have an open 3.31. Lol, and if I find one with a B6 code I'll be all over it, 3.73LS.

 

3.31 to 3.55 isn't enough of an upgrade to make it worth the hassle or the expense.

 

not even with the LS?

 

Not if you are trying to improve the towing performance. Start thinking 4.10's and an aftermarket LS/locker.

 

humm... i didn't think they even put 331s in the 00 f150, anyways glc is right with the 410s but if all you want is a LS than just buy a stock replacement from ford racing or something and keep your 331s you'll get better mpgs.

 

if you can find a 3.73ls rear end for under a grand, i say go for it. doing a complete swap that is.

if not, you can get new gears and locker installed usually for around 1,200 to 1,500.

 

I paid around 1000 total for my swap with new ring and pinion install and new for LS diff.

but i agree unless you get different gears for the ls its really not worth it

 

Rule of thumb is at least 2 ratios lower/higher to be worth swapping. For example if you wish to go with a lower(numerically higher) ratio and you have 3.31s you need to go with at least a 3.73 to be able to feel a difference or make it worth while.

 

I changed my 3.31:1 gears to 4.10:1 gears. LOVE IT!! Changed the gears out front and rear. I also put a Trutrac in the rear.
Im not 100% sure, but i belive the Expedition axles had different mounting points for shocks and they had coil springs. Like the previous posts have already mentioned, if the axle housing size (8.8, 9.75) on the two axles are the same, then you should be able to pull out the rear carrier and pinion and swap them out with yours. If they are not the same size (8.8 or 9.75), then a gear swap with a new set of gears, bearings would be the more likely choice. I have seen expeditions with both available axle sizes
Also, remember when you change the gear ratio, your computer will have to be re-flashed to make your speedometer read correctly unless you have a tuner which can take care of that issue. I also recall that for my year truck, the ford dealer i worked with could only flash the computer for up to a 3.73:1 ratio axle.

 

Not positive but I think Ford moved the vehicle speed sensor to the ring gear on the newer trucks. If that is true make sure you get the right set up. Somebody smarter than me might be able to verify this or call B.S. Just make sure before you dump a bunch of change into something you can't use.

 

the expedition rear axle is set up for IRS. it's not set up the same as our leaf spring over axle set up under the F-150.

hence, a direct swap out is not going to work. you would have to pull the internals out of the Expy axle, and put them in your F-150 axle. this is where it will get tricky and expensive.