I have a Std. Diff. on my 2004 F150 and am interested in an upgrade for my 2WD. When I go shopping I find different specs for the Ford 12 bolt. How many splines does it have 31 or 34, I have heard both. Sometimes 9" rear end is used as a discription, is this the same as 9.75?

 

Indeed, rear ends seem to be a big secret with these trucks. I've looked around a bit and I haven't found a damn thing.

I am very interested in regearing my truck, but frankly I don't know where to start as I don't have any idea what size my front and rear differentials are or how my splines they are.

I know they put different gear ratios in the 04-06 F-150's but did they put different sizes in these trucks or are they all the same?

Does anyone have resources (links) they can share on the subject to help me get started?

I'd love to have a pro do it, but I haven't been able to find anyone capable in my area yet. Though I am still looking.

 

GM axles are described by the number of rear cover bolts; Ford axles are described by ring gear diameter; Dana axles are described by model number. Crawl under your back bumper & look at the tags on the rear diff. One will specify the oil; the other will ID the axle. Here's how to read it:



AFAIK, the 8.8" 31-spline was used behind the 4.6L in 2WD F150s; almost all other FS trucks get the 9.75". According to DriveTrain.com:
Size: 9.75"
Lugs: 5
Splines: 34

 

Hey Thanks Steve, I appreciate the help.

 

Isn't that 6 Lugs?

 

I was quoting that website.

Isn't this thread pretty old to be proofreading?