HOW TO: Which late model Mustang rear differential do I have

 Here’s a little information on Late model Mustang rear axle ratios.

1979-2014 Mustangs came equipped with one of two Ford rear ends
Ford 7.5 differential  OR  8.8 differential

All ’79-85 Mustangs featured the 7.5 rear ends.

From ’86-2010 the Ford Mustang 8.8 rear end went into all V8 Mustangs (5.0L, 4.6L & 5.4L)
The 7.5” rear end went into all 4 cylinders (2.3L) and V6 Mustangs (3.8L).

The ’99-01′ & ’03-04′ Mustang SVT Cobras were equipped with an Independent Rear Suspension (IRS) that used the Ford 8.8” differential.
Starting in 2011, both the V6 (3.7L) & V8 (5.0L Coyote) Mustangs used the Ford 8.8 rear end.

All ’79-04′ Mustang Rear Ends used 28-spline axles except for the 2001 and 03-04 SVT Cobras – they used a 31 spline axle in their IRS rear end.

• The 2005-2010 V6 Mustangs with a Ford 7.5 rear end used 28 spline rear axles
• The 2005-2010 V8 Mustangs with 8.8” rear ends used 31 spline rear axles.
• For 2011-2014 Mustangs, both the V6 and 5.0L V8 Mustang were equipped with 31-spline axles.
  

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  Here’s something to note…  If you haven’t owned your mustang since it was new it may not be equipped with its original rear end from the factory!
  Many things may have happened have transpired over the car’s lifetime that may have resulted in a Rear-End it did not originally come with.
  Here are a few things to help you tell the difference between 7.5 & 8.8 rear ends.

THE FOLLOWING INFORMATION DOES NOT APPLY TO IRS EQUIPPED MUSTANGS

Compare your Rear End Differential Gaskets tin the image below: 
 7.5” rear ends have two flat sides and two rounded sides where the 8.8” rear end has four flat sides:

When working with a Rear Gear Set, here are a couple of things to check:

• Measure the diameter of the ring gear. A 7.5 Ring Gear will measure 7.5. An 8.8 Ring Gear will measure 8.8.
• You can also count the splines on the Pinion Gear. A 7.5 Pinion will have 28 splines & an 8.8 pinion will have 30 splines.

Hopefully, this sheds a little light on figuring out which Differential you have in your Mustang.