2005-2014 S197 Mustang Axle Guide

The more splines, the larger the axle which increases its strength. Stock axles are adequate for daily-driving and slight horsepower modifications, but if you plan to push more than 500 rear wheel horsepower, you should look into aftermarket replacements. The live axle rear ends on 2005-2014 S197 Mustangs came from the factory with upgraded axles in comparison to their earlier cousins. The 28 spline axles can hold up to around 400 rear wheel horsepower before breaking.

When considering which axle to buy, check if your rear differential will be compatible​, namely through spline counts. If you're aiming for a drag build, consider a set of rear axles with C-clip Eliminators.

• 2005-2010 Mustang 7.5" rear end used a 28 spline rear axle
• 2005-2010 Mustang 8.8" rear end used a 31 spline rear axle
• Starting in 2011, both the V6 and 5.0L GT Mustangs have a 31 spline, 8.8" rear from the factory

A 31 spline axle for the 8.8 differential is about 30% stronger than their 28 spline counterparts. Even though the newer 31 spline axles are stronger, they are still mass produced with minimal quality control, so they roll off the assembly line at a reduced cost. Many Ford OE axles are made of SAE 1055 or SAE 1541 hardened carbon steel. However, the hardening isn't across the entire depth, meaning the rest of the axle steel remains unhardened.

If you are going to be pushing more than 500 rear wheel horsepower and are planning to do some drag racing, you will want to strongly consider a high quality aftermarket axle set that has been built for the drag strip. Axles built to be subjected to the high torque and demanding stress loads are a must for any serious racer.

When looking at aftermarket axles for your particular Mustang, you will also want to check if your rear differential will be compatible with your upgrade. Moser, Superior, and Ford Racing are all excellent brands to choose from. You can either replace your axles with aftermarket versions that have the same amount of splines, or upgrade to an axle with more splines and a larger diameter for added performance. If you choose to use the same number of splines it is easier to install them yourself. If you are choosing to upgrade in size you will need to change the differential as well.

If you're planning on doing a lot of drag racing you should look into an aftermarket set of rear axles with a C-clip eliminator. Your factory axles are held into the rear end differential with C-clips which fit into a groove on the end of the axle. If these factory C-clips or the grooved end of the axle break, then the axle can come out of the housing tube, resulting in the whole wheel flying away from the car. NHRA rules ban C-clip axles on any Mustangs running 10.99 or quicker. The C-clip eliminator consists of a new axle bearing and a retainer plate. The plate bolts to the end of the axle housing, keeping the axle from coming out of the end of the housing in the event of a failure. Before you go dumping your clutch on the starting line at the strip, consider upgrading those axle shafts.