Mustang Rear End Gear Ratios & Axle Guide

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!

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MUSTANG RING & PINION TECH:

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Jump To: Ring & Pinion Tech | Axle & Rear End Tech |

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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!

WHAT REAR-END GEAR RATIOS CAME IN THE MUSTANG?

Factory Ratio	2.73	3.08	3.27	3.31	3.45	3.55	3.73
1979-93	87-93 V8 Manual	82-85 V8 Auto	86-93 V8 Auto	N/A	SVO w/7.5" Rear	N/A	N/A
1994-98	Available	Manual Only	Auto Only	N/A	N/A	N/A	N/A
1999-04	N/A	N/A	V6 | GT | 99-01 Cobra	N/A	N/A	Mach 1 | 03-04 Cobra	N/A
2005-09	N/A	N/A	N/A	V6/Auto GT	N/A	Manual GT	N/A
2010-14	Available	N/A	N/A	Available	N/A	Available	Track Pack | Boss
2015-17	N/A	N/A	N/A	V6 | Ecoboost	N/A	Performance Pack	Torsen Performance Pack
2018-21	N/A	N/A	N/A	Ecoboost 6-Speed	N/A	Performance Pack | GT Auto	GT Manual | GT350/R | GT500

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*graphic only includes the most common gear ratios*

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• 2.73
• 3.08
• 3.27
• 3.31
• 3.55
• 3.73
• 4.10

If you own any 1979 to current Mustang, 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, except for the 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 several years.

Gear ratios underwent several 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 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 remain with the same 2.73 standard rear gears for both Manual and Auto cars and 3.27 auto options and 3.08 manual options up until 1993 Mustang rear ends.

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.

Here are the most popular ways to correctly find out what rear-end gears are in your Mustang:

• Count The Teeth on the ring and pinion
• Check Your Vehicle Certification Tag
• Check The Rear Axle Tag

There are a few ways to find your rear-end gear ratio. You could count the number of teeth on the ring gear and 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 nine 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 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 your 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 with a low-mile, unmolested Fox Body, or if your Mustang is newer and the rear end has never been serviced, you may still have a Rear Axle Tag 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 that 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 we have mentioned because the tag could 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:

• WFCR | Part prefix ad suffix
• 3D18 | April 18, 1983 (Build Date)
• 3L08 | 3.08:1; L = Traction-Lok (SL has also been used to indicate Traction-Loc)
• 75 | Ring-gear diameter 7.5”
• S271D | Plant and model code; S = Sterling Axle plant

Most factory Solid Axle (Live Axle) Mustangs from 1979-2004 are equipped with the standard 28 spline axles, whether it be 4-lug or 5-lug. 2005-2014 Mustangs are equipped with 31 spline axles which are about 30% stronger than the factory 28 spline axles making them a popular aftermarket upgrade for 1979-2004 Mustang owners. Swapping over to 31 SPLINE axles will require the use of a 31 spline differential to function properly. These are great axles if you plan on taking your Stang to the next level!

• 79-93 Mustangs - 29 3/16" long rear axle.
• 94-98 Mustangs - 29 31/32" long rear axle.
• 99-04 Mustangs - 30 11/16" long rear axle.

When converting your Fox Body to 5 lugs, you have the option of Fox flange or SN95 flange axles. If you want to stick to drum brakes, the fox flange axles will work just fine. If you want to upgrade to a disc brake setup from a 94-04 Mustang, you will need the SN95 flange axles and a set of caliper brackets intended for the Fox length axles. The SN95 flange axles are hub centric to allow a perfect fit with any V6, GT, and Cobra 1994+ rotor options.

A popular swap among Fox Body owners is the 94-98 rear-end swap. This swap has gained popularity due to its low cost and less work. While this may seem the way to go, this also extends your track width by 3/4" on each side. This can cause tire rubbing and clearancing issues, as well as unforeseen issues with buying used parts. Using this rear end can also result in having to use different offer wheels on the rear of your Mustang. The 94-98 rear end consists of the same housing as the Fox, with axles that are .75" longer on each side. The 99-04 rear end has different, wider housing, and that, coupled with the longer axle, increases track width by 1.25" per side over a fox.

Before swapping out your ring and pinion in your Mustang, you first need to know what rear end is under your 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). Every version and model of the Mustang from 2011 to the current 2022 Mustang received an 8.8 rear end.

With the introduction of the S550 Mustang in 2015, Ford switch from a solid rear axle to an independent rear suspension (IRS). This was not the first time Ford used a 8.8 IRS. The SVT Cobras from 1999 until 2004 also used a variant of the 8.8 IRS.

Now that we have covered the original equipment information, we all know that the Mustang is one of the most modified muscle cars! That said, your car may not have the OE rear end anymore. Here are some visual cues to look for to help anyone identify with certainty what rear end is installed.

The 8.8” rear end is flat on the top and the bottom as well as the left and right. It has a square design with four rounded corners and ten bolts. When measuring from the top left bolt to the bottom left bolt, the 8.8” rear end will measure 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 the right and left and, like the 8.8” rear, has ten 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.

The following information does not apply to IRS equipped Mustangs