Would the rear axles on a 1984 F150 most likely be 28 spline or 31 spline? Is there a code either on the door sticker or on the tab on the axle that would tell me, or do I just need to get off my lazy butt and pull it apart and count?

 

1984 F150 should have 8.8". Be very careful purchasing anything seperately for the internal diff. carrier. In 1983 ?? Ford redesigned both L/S and open carrier and internal components.

Easy way to tell between early and late style 8.8: measure the diameter of the spider pin in the differential carrier. Early 8.8" had 3/4" dia. pin. Later 8.8" has 7/8" diameter spider pin.

Early vs late 8.8" diff's.--have different style of tooth cut (axle and spider gears) and internal carrier parts do not interchange at all.

If your diff. has a 7/8" spider pin, someone has updated it to a later model carrier.

If You don't want to remove cover, see if diff. has a rear cover with 10-bolts on it. You can call ford dealer with numbers on the tag. Tag may have number that starts with "S" or "V". Dealer can tell you from this number, what ratio and axle spline data that axle was built with. This will not confirm; however, that someone may have changed ratio or updated carrier to L/S or new style carrier. Good luck, Gearman

 

Thanks for the info. The original owner is a family member so I know that it has never been changed. I will look on the tag and see if I can get an anwser.