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FAQ: Rear End Ratios

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Poison Pinto:
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).


3     40     #   #     ####

This indicates a conventional 3.40:1 ratio.

Limited-Slip/Traction-Lok differentials will have an "L" between the numbers.

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:

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

C2-WGF-KI, -UJ, or -AA ..... 3.18:1
C2-WGF-AJ ..... 2.73:1

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.

If the tag is missing, or you suspect that the rearend has been modified, another way to tell the gear ratio is by jacking the rear of the car up, and put it on jack stands. Then mark one of the tires and the driveshaft. Slowly rotate the tire one full revolution, while counting the revolutions of the driveshaft. If you get 3 full turns of the driveshaft to one full turn of the tire, you have a 3.00:1. If you get a little over 4 full turns of driveshaft to one full turn of the tire, then you probably have a 4.11:1 ratio. This method is not exact, but it will get you in the ball park.

straw boss:
If you do that, you must make sure both tires turn exactly the same amount, or your reading will be off.  If the rear doesn't have limited slip, one wheel can lag behind the other when you are turning the driveshaft.
What I have done when that is a problem is lock one wheel so it can't turn, then count the turns of the driveshaft to make the other wheel turn two revolutions.  Sounds weird, but it works.

I have a rear end with tag numbers that read  WGF-AL-7J6

It came with but not in the pinto i just bought, and i haven't been able to find a code that matches it.  Does anybody know what this code is for or what it might be out of?  it looks like a 6.75"


What is the 2nd line of numbers on the tag?


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