Ford 8.8 Rear End ID Guide | Widths, Codes & 8.8 vs 9"
Since its inception, the Ford 9-inch rear has dominated the world of racing and hot rodding. Considered one of the strongest rear axle designs, the 9-inch is the king. Every king wants an heir, and in 1983, Ford gave birth to the 8.8 Ford rear axle design, finally giving us the progeny of performance potential we had been hoping for. The 9-inch ceased OEM production just three years later, so how has the prince of pinions performed? In other words, is the Ford 8.8 rear end ready to rule, or does it come up .2-inches short?
Originally built to replace the 9-inch rear, the 8.8-inch was first used (and currently still is) for both Ranger and F-series trucks and SUVs as a live axle (non-IRS). In 1986, the Ford 8.8-inch found a home in all V8 Mustangs, and from 2011 to 2014, it was used in all Mustangs regardless of engine. Ford opted to replace the 9-inch with the 8.8-inch, should you?
Why the 8.8 Rear End is Popular
Availability is often the precursor to popularity, and when something is really good, that translates to even more desire. The 8.8-inch rear end, in both live and IRS forms is one of the most prolific differential designs. Ford has built millions of these axles over the last 42 years, which means that you can find them cheap in the salvage yards, you don’t have to search long at all to find one, unlike finding an original Ford 9-inch housing, which has become quite difficult. These budget axles can be bought cheap, even in IRS form they typically cost $300-500 for the full suspension cradle through online marketplaces, making them excellent options for the budget builder.
If you have ever seen a car video on the internet, then you have certainly seen many a Mustang hitting telephone poles, billboards, and other cars a thousand times. That means that there are a million wrecked Fords in the junk yards, along with many of the “best selling truck in America.” While high demand drives up prices, high availability keeps them low. Cheap, reliable, and being readily available makes the Ford 8.8 rear axle an easy choice. But that doesn’t mean it is all lollipops and rainbows.
There are some inherent issues to the 8.8 design. Even though the 8.8 Ford differential is .2” smaller in diameter than the 9-inch, the pumpkin is larger, which can create some ground clearance issues for lowered vehicles. The pinion is not designed for high angle, which can cause issues for off-roaders, but more importantly, the 8.8 uses C-clip axles. One of the biggest strengths of the Ford 9-inch is that it uses bolt-in axles, so if an axle sheers, it doesn’t come flying out of the housing unlike a broken C-clip axle, which does. Additionally, the 8.8 is not as strong as the 9-inch, doesn’t have anywhere near the aftermarket support, and is somewhat limited in axle widths, making some vehicle swaps out of the question from the jump. The 8.8 uses a drop-out differential instead of the simpler third-member design of the 9-inch, making quick gear changes more difficult.
What Fords Have the 8.8 Rear End?
Where can you find an 8.8? Easy, just find a Ford truck, SUV, or full-size RWD car and there you go. It is just about that simple.
Ford 8.8 Live Axle Vehicles:
- 1983-2014 F-150 (Except some 4x4, Super Cab, and Lightning, which had the 9.75” rear)
- 1983-1996 Bronco
- 1985-2011 Panther platform (Crown Vic, Town Car, etc.)
- 1986-2014 Mustang (and other Fox chassis applications)
- 1986-1997 Aerostar 4.0L in 2WD only
- 1991-2011 Ranger 4.0L
- 1991-2001 Explorer (non-IRS)
Ford 8.8 IRS Vehicles
- 1988-1997 Ford T-bird
- 1999-2004 Mustang Cobra
- 2003-2010 Explorer/Mountaineer
- 2003-2005 Aviator
- 2003-2006 Expedition/Navigator
Ford Super 8.8 Axle
This specialty version used a 12-bolt cover (standard is 10-bolt), larger bearings, longer pinion gear with larger diameter, and 34-spline axles. This rear was used in 2015-up Mustang (IRS) and F-series (live axle).
While any 8.8 axle can handle routine use, the most sought-after versions are the 95-01 Explorer solid axle units, as they have the stronger 31-spline axles, disc brakes, built-in E-brake, and are readily available. For IRS units, the 2015-up Super 8.8 axle from the Mustang is the current go-to unit for high performance, but the Thunderbird 1999-2004 Mustang Cobra units are the most popular way to add IRS to any previously live-axle chassis. IRS for less than $500 is a no-brainer and you can’t even get remotely close any other way.
Ford 8.8 Rear End Identification
There are a bunch of variations of the 8.8 rear ends, including ratios, limited slip, and widths. Most 8.8s have an offset pinion gear like the 8-inch and 9-inch units, but Mustangs use a centered pinion gear position with equal-length axles. Car 8.8 axles used coil springs, while trucks use leaf springs, so the perches will match. Fox body 8.8s have a 4-bolt lug pattern, whereas most full-size cars, SUVs, and 1994-up Mustangs use the typical 5 on 4.5 lug pattern. F-150 and Bronco uses the larger 5 on 5.5 pattern until 2004 when F-series went to a 6-bolt lug pattern. Look for a ratio tag under one of the cover bolts and you'll find the ratio with an "L" for limited slip in many applications (3L27 is a 3.27:1 gear with limited slip). If the tag is missing you will have to remove the rear cover to verify if the differential is an LSD or open, Ford Traction-Lok diffs have an S-shaped spring clip in the center opening.
Limited slip (Traction-Lok) gear ratios: 2.73, 3.08, 3.27, and 3.55
Open diff ratios: 2.26, 2.47, 3.08, 3.27, 3.45, 3.55, 3.73, and 4.10
Axle tube diameter, note the axle tubes changed diameters several times.
- Mustang: 2.8”
- 90-09 Ranger: 2.8”
- 2010-11 Ranger: 3.25”
- Ranger/Explorer with 31-spline: 3.25”
- F150/Bronco w/ 31-spline: 3.25”
The 8.8 rear end uses a 4-bolt pinion flange yoke with either 1310 or 1330 U-joints, 1310 were used for most cars and SUVs, whereas the trucks typically have a 1330 U-joint. Some have an ABS sensor on the housing on the front driver’s side of the pumpkin. Ford 8.8 covers measure 11 inches top left bolt to the bottom right bolt. The top and bottom of the cover are flat on each side with radiused corners. Non-Super 8.8s have a 10-bolt rear cover, Supers have a 12-bolt cover. Some 90s-era Explorers and Rangers had a plastic diff cover.
Ford 8.8 Axle Tag Decoder
There are so many versions of the 8.8 rear end that you need to know how to ID them in the field. The axle tag is the easiest way to determine what is inside the case. The axle tags were bolted to the cover for early models and switched to a sticker on the axle tube in the late 1990s. The top line of the tag has a 5-letter code for the axle model, and a 4-digit code for the date (4A312= 1984, March, 12th). The bottom line includes the gear ratio, ring diameter (8.8), and the plant code. Limited slip models have an “L” after the first number of the gear ratio such as 3 L 73, which is a 3.73:1 ratio with limited slip. You can also check door sticker RPO codes, which vary by make and model.
How Strong Is a Ford 8.8 Rear End?
To put a fine point on it, 28-spline 8.8s are good for about 400hp in stock form. 31-spline units are more robust and support up to 700hp on street tires (not DOT drag radials or slicks). So, what if you are making 1000-hp or more? You can do it with an 8.8, but the cost to get there is equal or more than what it costs to swap in an aftermarket 9-inch housing, which gives you far more strength and durability for high-powered applications. The 8.8 is nearly a direct clone of the GM 12-bolt, which is legendary in its own right. The ring gears are the same size (8.8” vs 8.75”), the pinion rides on the ring gear at the center, which reduces parasitic loss, but also reduces the contact patch between the two gears, less gear mesh equals less strength. 31-spline 8.8s have the highest power rating and should be considered a good upgrade option. This requires changing the differential, as the axles must match the diff. Gears swap between both differential sizes, however. The stock 28-spline axles are 1.18” in diameter and are by far the most common.
C-clips work just fine on the street, but when an axle breaks, it is a big problem. All 8.8s are C-clip style, and frankly, that sucks. The bolt-in axles of a 9-inch are far superior. C-clip eliminators are not for street use (they are aluminum and can’t handle side loads), so if you want to safely switch to bolt-in axles, you need to weld on “big Ford” 9-inch housing ends. For autocross, drift, road-race, and high-performance street cars, a 9-inch live axle is more friendly. IRS 8.8s do not have this issue at all.
The axle tubes on all 8.8 rears have just two plug welds to the pumpkin. It is not uncommon for the plug welds to break, allowing the tube to spin in the housing. Use a high nickel welding rod to fully weld the tubes to the housing. For LSD models, the OEM Traction-Lok diff is OK, but it is not the strongest option. Aftermarket upgrades are well worth the expense when you have 400-plus hp. Upgrades include 4-pinion differentials, carbon fiber clutches, and aftermarket diff swaps.
Ford 8.8 Swap vs Ford 9" Swap
The 8.8 Ford rear end became so popular because it is the OEM replacement for the 9-inch, making it cheap and easy for many platforms. If you want a budget rear axle upgrade, the 8.8 is the best deal around. OE Ford 9” housings are very hard to find, so cost-wise, an 8.8 makes a lot of sense for a street car. Higher-performance applications will find that the 8.8 costs just as much as a 9-inch to upgrade, but is inherently weaker. You have to consider all things when looking at a rear axle upgrade.
Aftermarket 9-inch housings, such as Speedway Motors’ fabricated housing and axle kits can be had for around $2k, including the housing, axles, and third-member with differential making it an easy choice. Couple that with the fact that the kits are available in chassis-specific and universal width options, you can go from a fabrication-heavy Ford 8.8 swap to a direct bolt-in swap that greatly simplifies the entire process. The Ford 8.8 rear end has been around for over 40 years, but it is the 9-inch that wins the parts availability award. You can certainly find just about any go-fast goodie for the 8.8, but you can get it bigger/beefier/cheaper for the 9-inch in most cases. The 8.8 also needs some support for the differential cap girdles in high-performance applications. The bottom line is this: mild to mid-level street applications are well served by an 8.8 in most cases.
Get beyond the 500hp range and you have to start upgrading the 8.8, whereas an aftermarket 9-inch axle is already stronger than an OE 9-inch housing. When upgrading, the costs level out between the two, and the 9-inch is actually cheaper in the long run if you need more power handling. Whether you have a vehicle with an 8.8 already or are looking to upgrade to one, it is hard to go wrong with an 8.8 axle, just make sure that it will serve your needs before making the final decision. Regardless of what direction you go, Speedway Motors has the parts you need to get your ride back on trac(tion).
