Upgrading your Mustangs rear axles is an easy way to beef up your drivetrain and add in new components. Most Fox Body Mustangs came stock with a 28 spline, 4 lug axle which is fine for stock applications, but there is always room for improvements. Follow along as we guide you through stock replacement and performance Mustang axles.
28 Spline Axles Vs. 31 Spline Axles
Most factory Mustangs are equipped with the standard 28 spline axles whether it be 4 lug or 5 lug. A 31 spline axle is about 30% stronger than the factory 28 spline axles making them a popular aftermarket upgrade for all Mustang owners. Swapping over to a 31 spine axle will require the use of a 31 spine differential to properly mate up. These are great axles if you plan on taking your Stang to the drag strip!
Fox Length Axles Vs. SN95 Length Axles
- 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.
SN95 Flange Axle
When converting your Fox Body to 5 lug, you have the option of Fox flange or SN95 flange axles. If you are wanting to stick to drum brakes, the fox flange axles will work just fine. If you are looking to upgrade to a disc brake setup from a 94-04 Mustang, you are going to need the SN95 flange axles along with a set of caliper brackets. The SN95 flange axles are hubcentric to allow a perfect fit with the 94+ rotors.
SN95 Rear End Swap Into Fox
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 involved. While this may seem like the way to go, this also extends your wheelbase by 3/4" on each side. This can cause tire rubbing and clearancing issues, as well as unforeseen issues with buying used parts. 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 a different, wider housing and that coupled with the longer axle increases track width by 1.25" per side over a fox.
Difference Between 7.5" & 8.8" Rear Ends
If you own a 1979-2014 Mustang, then it came equipped with one of the two Ford rear ends – Ford 7.5 rear end or the Ford Mustang 8.8 rear end. All 1979-1985 Mustangs featured the 7.5 rear end. Starting in 1986 Ford introduced the popular 8.8” rear end in the Mustang. From 1986-2010 the Ford Mustang 8.8 rear end went into all V8 Mustangs (5.0L, 4.6L and 5.4L) and the Ford 7.5” rear end went 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, both the V6 (3.7L) and V8 (5.0L Coyote) Mustangs used the Ford 8.8 rear end.
Ok so you know what Mustang rear axle assembly
went into what years – now let’s look at what axles are in your Mustang rear end. All 79-04 Ford 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 whereas 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.
Now that we've cleared up the issue of what rear end you have and what Mustang axles
are in your rear end cleared up - does this mean that your Mustang is still equipped with the rear end that it had from Ford? No! Many things could have transpired over the years to have let your Mustang end up with a Rear End it did not originally come with. Here are a few things to help you differentiate between a 7.5 & 8.8 rear end.
The following information does not apply to IRS equipped Mustangs
Compare your Rear End Differential Gaskets to these pictures to start off with – 7.5” rear ends have two flat sides and two rounded sides where the 8.8” rear end has four flat sides:
If you are only 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.
With this new information you should be able to easily tell what rear end you have in your Mustang!