I have a 99 F150 XL Stepside 5.4L
Looking at the Vehicle Tag Code for the axle it says 26 but thats for an 250?
Anyways the axle tag says
3 S 924 A
3 73 9 75 8M18

I guess know it 3.73 gears but beyond that? I want to install a posi or true locker so I'm trying to find out the spline #. Thanks

 

It's a standard Ford 9.75" rear. I recommend a Detroit Truetrac.

http://www.summitracing.com/parts/dtl-913a477/overview/

 

That's a 3.73 ratio , 9.75" NON-LS diff ( the '3.73' would have an 'L' after it if it was a Traction-Lok). All Ford 9.75's are 34 splines.

http://www.differentials.com/technic...identification

http://www.fordification.com/tech/rearends_ford15.htm

good luck
MGD

 

Thanks guys that helps a lot, THanks