Before you embark on the rebuild and start scouring local scrap yards and online websites, it will be helpful to understand what to look for and what to avoid in these axles.
First, you need to understand some fundamentals of the Ford axles to help guide your quest. I have spent countless hours over the years collecting, reading, and studying old shop manuals, supplier reference documents, SAE papers, and even vehicle manufacturer reports and notes. Some of this information is very important as it is becoming more and more difficult to find documentation on axles and differentials that were built more than 40 years ago. I have also spent many hours in scrap yards and visiting and interviewing the experts in this field along with years of building numerous axles myself. In this chapter I share a summary of decades of work on these axles.
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There is a very fundamental difference between Ford’s 8.8- and 9-inch axles. I reference these axles based on the ring gear nominal outside diameter in inches. The fundamental difference between these axles is how the gears are supported and which end of the axle housing (front or back) that they are assembled from.
It may seem strange to begin by comparing the 8-inch to the 9-inch axle, but there is an important distinction to make since the 8-inch axle is weaker than the 9-inch. Many people are not aware that Ford made a smaller banjo axle and confuse the 8-inch for a 9-inch.
The 8-inch was introduced in 1962 and is found in many lower performance Fairlanes, Mustangs, Falcons, Comets, Cougars, and Pintos, just to name a few of the applications.
There’s an easy way to tell an 8-inch apart from a 9-inch. All of the 8-inch case nuts can be accessed with a socket. In contrast, on the 9-inch, two nuts on the bottom at about the 6 and 7 o’clock positions cannot be accessed with a socket and require a wrench.
Both axles share a common design and are often referred to as banjo style or third-member style. The smaller 8-inch just cannot handle the abuse as its bigger brother can. The 8-inch also was only available with 28-tooth axle shafts. Unless you are building a Pinto or straight six-cylinder vehicle, you want to avoid it.
Both 8- and 9-inch axle housings are made from a series of stampings that are fixtured and welded together. This complex fixturing and welding process, coupled with fuel economy concerns, is what eventually led to their production demise. These axles had a stout 2.25-inch ring gear offset as compared to a 1.5-inch ring gear offset of the later 8.8-inch axle.
The larger offset is better for strength and noise but worse for sliding and efficiency. While the larger offset makes the ring and pinion gears stronger, the additional sliding of the gear teeth creates more heat in the axle. Therefore, these axle assemblies require better quality oil and good underbody airflow to keep the unit cool. With their high-volume production, the two biggest quality problems were leaks from poor welds and poor alignment of the housings. So don’t be surprised that most of these axles leak from the welds. Careful aftermarket shops and their stringent attention to repairing these housings are able to correct many of these issues.
The Ford 9-inch has a reputation as a durable axle that can transmit enormous torque, and this is rightfully deserved. Some even consider these axles to be bulletproof. This is by far the most common axle used by restorers, hot rodders, customizers, and racers. It has enjoyed a long production history with many variants. There is a huge aftermarket support for this axle design. Many companies, such as Currie Enterprises, Mark Williams Enterprises, Moser Engineering, and Strange Engineering, reproduce this design today. It is still used in NASCAR racing as well.
Because of the long production history of this axle, many variants are available. Most of the time, the differences are in shock and spring mounting brackets and, of course, brake hardware. It is a banjo-style axle as is the 8-inch. It was in production on many Ford cars and trucks, first appearing in 1957 and finally replaced by the Salisbury-style 8.8-inch axle in 1986, saving about 50 pounds and boasting increased efficiency.
The 9-inch’s very large pinion offset of 2.25 inches requires the pinion to be straddle mounted, which refers to the fact the pinion head has bearings that straddle it on either side. There is a machined roller bearing race on the pinion head portion that points at the differential opposite the tapered bearing races. This additional bearing and, more importantly, the necessary casting support structure is what drives the larger hypoid offset. The additional straddle mount pocket bearing provides additional support to the pinion head during high-torque events. This bearing is one of the reasons that the 9-inch has the reputation for being bulletproof.
There are three bearings on the pinion shaft: the two traditional tapered roller bearings for the head and tail bearings with a third cylindrical roller bearing on the opposite end of the pinion head. In order to allow for the additional straddle mounted bearing and casting support structure, the hypoid offset needs to be large enough to clear the differential case. Hypoid offset is the distance between the centerline of the pinion and the centerline of the ring gear. This is 2.25 inches for the Ford 9-inch and 1.5 inches for the 8.8-inch axle.
People have been climbing around scrap yards for years to find the best examples of the 9-inch axle. If you are fortunate enough to find an axle with the identification tag still attached, it will help solve part of the mystery of what application the axle came from and what might still be inside.
The axle identification tag is located at about the 3 o’clock position under the third-member mounting nut when you are looking straight at the front of the axle. These tags are typically quite beat up, twisted, and rusted over the years. These tags were not that informativeon the early units, so from 1957 to 1962 the tag just referenced axle ratio. In 1963, Ford included more information.
The axle tag typically has two lines of numbers and letters stamped on it. The format has changed over the years but mostly follow this sequence:. The top line typically starts with a three-digit axle model code (or the prefix of the part number), followed by a dash, and then the suffix. The axle model codes are interchangeable, typically the suffixes are different for a revision change but the axle is still interchangeable with one having the previous suffix. There may be a second dash and more numbers and letters on the top row if there are specifics that are unique for interchange information. Typically with just this information, you can cross reference what you need to know about the axle. The last set of digits on the top row on the right side is the date code.
The bottom line begins with the ratio being the first set of numbers. If an L is included, it was equipped with a limited-slip differential or Traction- Lok. The middle number is the ring gear diameter in inches, typically an 8 or 9. The last set of numbers is the vehicle plant code.
If the axle tag is missing, as most are, you need to remove the third member in order to know what ratio you have and if it has a limited-slip or not.
Don’t be surprised if the tag you have does not exactly match this. There are also unique domestic special-option tags, which don’t follow the format.
The date code is stamped on the tag. The first number is the last digit of the model year of the decade, the next digit is a letter and represents the month (A is for January, B is for February, and so on), and the last two digits represent the day of the month. This format is also applicable to casting date codes.
Some tags reference the week of the month instead of the exact day and just use a letter (A to E) for first through the fifth week of the month.
You are looking for a nodular iron case, with its telltale “N” cast into the front or inside wall. These third members are the strongest of the production cases and the most desired. Aftermarket vendors are actually re-casting these cases in very strong nodular iron, so more often than not it is easiest just to purchase a new case.
But if you’re looking for an original, they can be spotted quite readily even without an axle identifycation tag. The N cases had two vertical ribs, three horizontal ribs, and a machined-in fill plug. There are four versions of the nodular iron third members that were produced from the factory. These first became available on the 1964 Galaxies with the 427-ci engine and were found on many higher horsepower cars and trucks.
Of the four versions of the N case, three have an actual “N” cast into it right above the pinion cartridge.
The fourth version did not have the “N” in the casting on the outside but still retained the rib structure. In order to verify a nodular unit, you need to look on the inside of the casting. These have a C4AW-4025-B casting part number next to the adjuster nut.
Of course, if your budget allows, you can purchase an aftermarket iron case that is stronger than any factory case. If you are looking for an N case or think that you have found one of these desirable axles, make certain to examine it closely. The WAR, WAA, and WAB cases have the same ribbing as the N case, but are missing the ever important “N” feature.
Any of the W-series cases do have a fill plug machined in them. Both standard and W-series cases are made out of gray cast iron. Only the N-series cases are made out of the stronger, more desirable, nodular iron. While the iron is molten, magnesium is added to increase the shear strength of the alloy. The magnesium addition causes the grain structure to change from flakes to nodules and thus the name “nodular” iron. The N cases typically came with the larger Daytona-style pinion support bearing, and 31-spline axle shafts.
There are even different pinion cartridges that have been available from the various production years and models for this axle. The Daytona- style cartridge allows for a larger pinion head bearing when compared to the standard pinion cartridge. This is a great upgrade component to use for high-power applications or if you are replacing your cartridge.
Like most Ford axles, the 9-inch has a single hypoid ring gear mounting distance, so, unlike the Dana and GM axles that require unique differential carriers based on ratio, a single differential carrier works with all of the Ford ratios. Also, since this axle is used in so many circle-track race cars, the 9-inch enjoys an unparalleled availability of different gear ratios in the aftermarket.
This is when making a few phone calls to reputable axle builders can be helpful. There are quite a few companies making Ford 9-inch housings to fi t just about any muscle car out there, including non- Ford vehicles. (See Chapter 8 for how to install a 9-inch in a classic 1957 Chevy Bel Air as a performance upgrade.)
The axle housings themselves had many different variations over time as well. These variations include different-size drum brakes, disc brakes, and wheel hub arrangements.
Since these housings were a series of stamped-steel pieces all welded together, there were many different overall lengths, tubes sections, mounting brackets, and even general constructions over the years (see Chapter 5).
The Ford 8.8-inch is very similar to the General Motors (GM) 87⁄8-inch, 12-bolt axle. Some differential experts tell you that the Blue Oval engineers copied the 12-bolt design when they came up with the 8.8-inch axle. While the 8.8 is similar to the 12-bolt, it isn’t identical. Interestingly, the Ford axle uses the exact same size of tapered roller bearings as the GM 12-bolt. The Ford version uses larger axle shafts and different lube flow strategy. These axles did have metal axle tags similar to the 9-inch axles but they were slowly phased out as vehicle programs were updated. There are several reasons for this.
Cost and complexity are two. These tags provided information for the service technicians but wasn’t that important for the vehicle assembly plants. The third reason was basic health and safety concerns for the assembly technicians and other employees who handled the axles in the manufacturing and assembly plants. There were many instances of cuts and scratches from the thin steel tags sticking up on the axles.
The tags were replaced with adhesive labels that are placed around the axle tube near the brake and wheel end. These labels have a specific code that is similar to the axle code on the 9-inch axles.
The Ford 8.8-inch axle has the same ring gear mounting distance (see Chapter 7) for all ratios, just like the 9-inch. So again, unlike the GM and Dana axles that require a unique differential with different ratios, the Ford 8.8-inch differential is common across all of the ring-and-pinion ratios. There is a ton of aftermarket support for this axle (see Chapters 3 and 4 for more details).
The 8.8 is a traditional semi-fl oat Salisbury axle with C-washers for axle retention. Many people prefer to just call it the Ford 9-inch-style wheel end. But to be correct, it is a 3/4 fl oat. There are 8.5-inch gears installed in these housings for lowerpower vehicle applications. The typical 3 inch-diameter tubes can be a bit flimsy in higher-power applications.
The 8.5- and 8.8-inch gears have even found themselves in the independent-carrier-style axles. The Ford Mustang and Thunderbird used this style for a few model years. There were also 8-inch ring gear independent carriers in production.
Written by Joe Palazzolo and Republished with Permission of CarTech Inc