I keep searching around without reference… Are our 57 F100 rear ends a 28 or 31 spline differential?

Thanks in Advance

 

Mine was 28 spline. It's not difficult to change over to 31 spline if you're willing to $pend $ome money.

BTW 28 spline is fine for anything but really serious horsepower.

 

Pulling an axle after the game :P

Thanks for the quick reply!

 

Just pulled both axles. 28 spline meaning the 65 3rd member I picked up today will fit perfect!

 

B7TZ-4234-A .. 28 Spline 9" Axle Shaft-R/L is the same ~ 1957/67 F100.

Some 1968/72 F100 9's have 28 spline axle shafts, some 1968/72 F100 9's have a 9 3/8" ring gear with 31 spline axle shafts.

CAVEAT EMPTOR - Let the buyer beware. If the "1965 3rd member" is from a car, it could have 28 or 31 spline axle (aka differential) gears.

 

I found the cause of the issue. It looks like in the past a wheel bearing must have came apart and sent a ball bearing down in the pumpkin. After removing the 3rd member I could see damage on both the pinion and ring gears along with metal in the housing.

I ended up pulling a 65 F100 3rd member which was an exact match outside of the C4AW case (1 bar + no filler plug). Backlash is with-in spec so I didn't rebuild or change seals. Everything went together with a breeze and the truck is now running with no rear end noise!!