MBDiagMan

If you can get an extension and socket on the bottom two nuts then it's an 8 inch. If the extension and socket won't go due to the front portion of the third member hanging down in front of the nuts, then it's a nine inch. Simple as that.

dbgrigsby93

I know that my gears are original 2.75's. Can that tell u anything as to what would have come from the factory?

pass1over

This is the easiest way to find out if you have a 8 or a 9 inch rearend.


To figure out the ratio, jack rear up, mark driveshaft and wheel, spin tire 1 full revolution, count how many times the driveshaft spins

Randys66gt

The 8" had 2.79 gears in the automatic as stock gears and the 9" that started in 67 Mustangs had a 3.0 gear. If it is a 9", it was a transplant like mine.