Ford 8.8 Strength Comparison
The truth is that the Ford 8.8 is virtually a clone of the Chevy 12-bolt and therefore almost as strong. Most rear axles are described by their ring-gear diameters, with larger being better. A Ford 9-inch has a ring-gear diameter of, you guessed it, 9 inches closely followed by the 12-bolt at 8.875, with the Mustang rear at 8.80 inches. Another strength consideration is pinion-shaft diameter. Here, the 8.8 and the 12-bolt are identical at 1.625 inches and in fact use the same pinion bearings. By comparison, the Ford 9-inch pinion shaft measures only 1.313 inches. The Achilles' heel of the stock 8.8 Ford rearend is its 28-spline axles, especially when compared to the Chevy 12-bolt's stronger 30 splines. Ford eventually rectified this oversight and upgraded the '94-'99 Mustang 8.8 rears with 31-spline axles and larger axletubes. These rear-axle assemblies are now beginning to populate the recycling yards and should be available at a decent price. These housings are slightly wider than the '86-'93 housings and may actually fit some of the wider leaf-spring-car requirements, so keep that in mind as well.
The point of all this is that the Ford 8.8 has all the basic components to create a performance rearend; it just needs a little aftermarket help to make it stronger. The original Fox-body 8.8 used from '86-'93 can be easily upgraded with better axles, a stronger limited slip with more clutches, and bigger axle bearings to become a very durable yet light rearend assembly. And the best part is you won't spend a ton of money to get there.
Pumping Iron-Strength-Building The 8.8
The keys to bulking up the 8.8 Ford are pretty simple. If you are planning to put at least 400 hp through a Ford 8.8, the first step is better axles. Rather than buy aftermarket 28-spline axles, the smart move is to upgrade to stronger 31-spline pieces. This will also require a 31-spline limited slip. Moser, Strange, and others offer both better axles and several choices when it comes to differentials with the clutch-type Eaton-style limited slips being the least expensive. An excellent choice if you plan on doing both drag racing and abusing the apexes on the occasional road course is Eaton Detroit Truetrac gear-style limited slip. This unit is more expensive but applies the power in a corner more efficiently than clutch-type units and will not wear out in your lifetime.
If your plans include going really quick on the dragstrip, there is a C-clip safety issue that also needs to be addressed. NHRA bans C-clip axles on any car running 10.99 or quicker. C-clip rearends are dangerous because if you break an axle, the axleshaft can slide right out of the housing and push the tire into your quarter-panel. While there are loads of C-clip eliminator kits out there, there's a better solution. The smart move would be to invest in a set of big-bearing housing ends from Currie, Moser, or Strange, and have a professional shop cut the stock 8.8 housing ends off and weld these larger ends in place. Strange, for example, offers a housing end that will accommodate a much larger Ford axle bearing and a matching retaining strap yet maintains the 8.8 Ford bolt pattern. This allows the choice of stronger 31-spline axles combined with a larger axle bearing. Currie, Moser, and Strange (among others) offer several axle choices. This makes for a killer combination that is mucho strong.
 Like most 5.0 Mustangs, the...  Like most 5.0 Mustangs, the 8.8 we pulled out of our wrecked Mustang already had a Traction-Lok limited slip but was fitted with 2.73 gears. You can spot a Traction-Lok by the S-shaped preload spring in between the side gears in the differential. |
 The pinion-gear shaft diameter...  The pinion-gear shaft diameter is the exact same size as the Chevy 12-bolt and larger than a 9-inch. This is a 12-bolt Chevy pinion gear. |
 Here's a comparison of a stock-axle...  Here's a comparison of a stock-axle bearing and the much larger Ford 9-inch-style axle bearing. When it comes to axle bearings, bigger is better. |
 The solid-pinion bearing spacer...  The solid-pinion bearing spacer eliminates the need for a crush sleeve and also offers the advantage of being able to easily change the pinion seal or remove the pinion without having to torque a new crush sleeve. |