One frequently asked question is how to tell what the gear ratio of the rear end is. This is especially true if looking at a rear end that is out of a car or if you know that the rear end in a car is not the original unit. Provided the rear end itself has not been modified, the following information should help you determine the gear ratio of your rear end.
The rear end case should have a small metal tag. On the 6.75" differential, this is on a bolt that holds the back cover on.
The tag has several codes on the top and bottom edges.
The easiest method is to look at the numbers on the bottom edge. This is useful if you're looking at a non-Pinto rear end (such as an 8" rear end out of a different Ford model).
Example:
3 40 # # ####
This indicates a conventional 3.40:1 ratio.
Limited-Slip/Traction-Lok differentials will have an "L" between the numbers.
Example:
3 L 40 # # ####
The original 6.75" rear ends put in 4 cyl and some 6 cyl Pintos have codes along the top edge that should comply with the following:
1975-76
C2-WGF-H or -K ..... 3.40:1
C2-WGF-U, -R2, or -AA ..... 3.18:1
C2-WGF-N or -R ..... 3.55:1
1977-78
C2-WGF-KI, -UJ, or -AA ..... 3.18:1
C2-WGF-AJ ..... 2.73:1
1979
C2-WGF-AM ..... 2.73:1
C2-WGF-AN ..... 3.08:1
C2-WGG-C ..... 2.73:1
C2-WGG-D or -E ..... 3.08:1
The "C2" in the code denotes a conventional rear end.
Sources: Haynes Auto Repair Manual for 1975-1980 Ford Pinto & Mercury Bobcat;
www.mustangii. org/decoder/axle.