Hello
I just installed a 12" Rize lift with 37 inch Boggers on my 07' F150 FX4. The calculator that I used on 4wheelparts showed that a 4.40 be what I need. The next thing up is 4.56 and that may be what I want since I'm going up to a 38" tire in a couple of months. The problem is that I can't even figure out for 100% sure which differentials I have. I've been to every web site and all forums but this one and they all say look at the bolt pattern or the tag. Well I can't read the tags on my rear or front differential because of excessive paint. It's a 12 bolt rear end if that tells helps at all. I know for sure that I have 3.73's but no clue as to which differential I have. Can anyone help me out?

 

You have an Ford 8.8 inch IFS with 28 spline axles in front

DO you have a 5.4L engine? If yes, Ford 9.75 34 spline long (12 bolt large)
If no, Ford 8.8 31 spline (10 bolt small)

 

If he's going to be running 37's or 38's I hope he's got the 5.4!

 

I agree with you there

with that lift i would put 4.88's minimum, and if hes serious about 44's, probably 5.14/5.13's minimum.

FX412inch, are you hinting at a SAS? Do your rears now, go easy on the truck, dont 4 wheel it, and then install gears in the D60 or whatever you are using when you install it.

 

I would skip right over 4.56 and go with 4.88 or something even shorter if you are gonna run 38s.

 

Jordan, thanks for recommending the 4.88s a few months back. I went ahead and did it 2 weeks ago. Best mod yet!