The Ford Mustang rear end specifications have changed quite a bit since the beginning of the Fox Chassis in 1979. From the measly 2.26:1 gear found in some of the first years of the Fox Body Mustang to the 3.73:1 ratio found in some of the most current performance models, Ford has offered factory gear choices to fit almost every driving style! Use this guide to have your Mustang gear ratio explained!
|2.73 (87-93 V8 Manual)||2.73||3.27 (V6/GT/99-01 Cobra)||3.31 (V6/Auto GT)||2.73||3.31 (V6/Ecoboost)||3.31 (Ecoboost 6-Speed)|
|3.08 (82-85 V8 Auto)||3.08 (Manual)||3.55 (Mach 1 | 03-04 Cobra)||3.55 (Manual GT)||3.31||3.55 (Performance Pack)||3.55 (Performance Pack/GT Auto)|
|3.27 (86-93 V8 Auto)||3.27 (Auto)||3.55||3.73 (Torsen Performance Pack)||3.73 (GT Manual)|
|3.45 (SVO w/7.5" Rear)||3.73 (Track Pack/Boss)||3.73 (GT350/R | GT500)|
If you own a 1979 to current Mustang, then it came equipped with one of the two Ford rear ends – Mustang 7.5” rear end or the Ford Mustang 8.8” rear end. All 1979 Mustang rear axles through the 1985 fox body Mustangs featured the 7.5” rear, with the exception of the very first year of the Fox that was equipped with a “carry-over” 6.75” rear end from the Mustang II that was only behind the 4-cylinder and 6-cylinder variants.
Starting in 1986, Ford introduced the popular 8.8” rear end in the V8 Mustang to support the 285 lb/ft of torque that the 302 began to produce. The 8.8” rear end is a much stronger option than the weaker 7.5” option which would remain as the 4-cylinder and v6 options for a number of years.
Gear ratios went through a number of changes and options through the first years of the Fox Chassis. Some very tall gears were used in 1980 and 81 having 2.26:1 ring and pinion gears with 1981 also having the 3.08:1 option. Starting in 1982, the tallest gear option you would find in the rear end of this pony car was a 2.73:1.
Consistency with ring and pinion gear options would begin in 1988 and would remain with the same 2.73 standard rear gears for both Manual and Auto cars and having 3.27 auto options and 3.08 manual options up until the 1993 Mustang rear end.
From 1986-2010, the Ford Mustang 8.8” rear end would be used for all V8 Mustangs, and the Ford 7.5” rear end was installed into all 4 cylinder (2.3L) and V6 Mustangs (3.8L).
The 99-01 and the 03-04 Mustang SVT Cobras were equipped with an Independent Rear Suspension (IRS) that used the Ford 8.8” differential. Starting in 2011, the V6 (3.7L) was upgraded to feature the same Ford 8.8” rear end found in the V8 (5.0L Coyote) Mustangs.
One of the first steps to knowing your Mustang rear axle ratio is knowing which rear end is actually under the backside of your pony car. As we have already covered, all 1979-1985 Fox Body Mustang rear axles featured the 7.5” rear. Then, from 1986-2010, the Ford Mustang 8.8 rear end went into all V8 Mustangs and the Ford 7.5” rear end now went into all 4 cylinder (2.3L) up to 1993 and V6 Mustangs (3.8L). Continuing from 2011 to the current 2021 Mustang, each model from the MUstang GT all the way up to the flagship Shelby GT500 has a variant of the 8.8” rear end.
Now that we have covered the original equipment information, we all know that the Mustang is one of the most modified muscle cars in existence! That being said, your car may not have the OE rear end anymore. Here are some visual cues to look for helping anyone to identify with certainty what rear end is installed.
The 8.8” rear end is flat on the top and on the bottom as well as the left and right. It has a square design with 4 rounded corners and has 10 bolts. When measuring from the top left bolt to the bottom left bolt, the 8.8” rear end will measure at 11” from bolt to bolt.
The 7.5” rear end is also flat on top and bottom. However, the visual difference comes in where it is rounded on right and left and, like the 8.8” rear, also has 10 bolts. When measuring from the top left bolt to the bottom left bolt, the 7.5” rear end will measure at 10” from bolt to bolt.
There are a few ways that you can find your rear end gear ratio. You could count the number of teeth on the ring gear then divide that number by the number of teeth on the pinion gear. An example would be if the ring gear has 37 teeth and the pinion gear has 9 teeth, the gear ratio will be 4.11:1. In other words, for every single turn of the ring gear, the pinion will turn 4.11 times.
With a rear end gear ratio of 3.73, the pinion will turn 3.73 times for every one turn of the ring gear. For a 4.10, the pinion will turn 4.10 times.
For a method to manually find out what gear set is installed in your Ford Mustang rear end and for more info on a performance upgrade for your Mustang, check out our 3.73 Gear Ratio vs. 4.10 Ratio article!
Another way to determine your rear axle gear ratio is to open the door and look for the Vehicle Certification (VC) tag. Mustang rear end code characters that indicate whether your car has a limited-slip differential or an (open) conventional differential as well as your rear axle gear ratio can be found on the lower right section of the VC tag, labeled “AX”. This tag, also known as the “data plate”, can be found on the driver side door lock face or the B-pillar depending on the year that you Mustang.
For 2005 to current Mustangs the VC will list the gear ratio under the section labeled “AXLE”.
Refer to the following data to help identify what gear set you may have:
If you are one of the fortunate ones who have a low-mile, unmolested Fox Body, or if your Mustang is newer and the rear end has never been serviced, then you may still have a Rear Axle Tag still present. The code that is stamped into the tag contains the plant code, the gear ratio, the build date, and ring gear dimensions.
Keep in mind, if your tag is missing, you can refer to the methods mentioned above to identify your current gear ratio and rear-end size. Even if your tag is present, always use the methods that we have mentioned because the tag could even have been changed during your Mustang’s life and provide incorrect information.
Below is what your tag may look like:
This is broken down as follows:
Now that we have covered which Mustang rear axle assembly went into their specific years, let’s look at what axles are in your Mustang’s rear end. All 79-04 Ford Mustang Rear Ends were equipped with 28 spline axles with the exception of the 2001 and 03-04 SVT Cobras. They came from Ford with 31 spline axles in their IRS rear end.
Popular upgrades for the 28 spline-equipped cars involve removing the OEM differential and axles and replacing them with a stronger 31 spline differential with matching 31 spline axles. The splines must be matched up whereas a 31 spline axle will not match the splines with a 28 spline unit.
The 2005-2010 V6 Mustangs with a Ford 7.5 rear end used 28 spline rear axles, however, the 2005-2010 V8 Mustangs with 8.8” rear ends were upgraded and came standard with the stronger 31 spline rear axles. For 2011-2014 Mustangs, both the V6 and 5.0L V8 Mustang were now equipped with 31 spline axles.
Check out our brief article on 28 vs. 31 spline axles!