Overview
The rear axle is one of the most critical components in any F100 — it determines your truck’s towing capacity, acceleration, highway RPM, and overall durability. Ford used several different rear axle assemblies across the seven generations of the F100, and understanding which one is under your truck (and which ones you might want to swap in) is fundamental knowledge for any owner or builder.
Factory Rear Axles by Generation
Banjo-Style Rear End (1948—1956, Generations 1—2)
The earliest F-Series trucks used a banjo-style rear axle housing with a removable center section accessed through a rear cover. These are semi-floating axles with a relatively low load capacity by modern standards. They work fine for stock or lightly modified trucks but are generally replaced on any build where increased power or payload is part of the plan. Gear ratio options were limited, typically 3.73:1 or 4.11:1 from the factory.
Ford 9-Inch
The Ford 9-inch is the most famous rear axle in American automotive history, and for good reason. Ford used variations of the 9-inch in F100s from approximately 1957 through 1979 (Generations 3—6), making it the longest-serving rear axle in the F100 lineup. The 9-inch is a drop-out center section design — the entire third member (carrier, ring and pinion, bearings) removes from the front of the housing as a unit. This makes gear changes and rebuilds far simpler than other designs.
Key features of the Ford 9-inch:
- Removable third member for easy swaps and bench rebuilding
- 28-spline or 31-spline axle shafts depending on application (31-spline is the stronger option)
- Nodular iron or aluminum center section options
- Gear ratios from 2.75:1 to 4.56:1 were available from the factory; aftermarket ratios extend even further
- Massive aftermarket support from companies like Currie Enterprises, Strange Engineering, Moser Engineering, and Richmond Gear
The 9-inch is widely considered the strongest production rear end ever put in a half-ton truck, and its aftermarket support is unmatched. Many F100 builders who have a different rear axle will swap to a 9-inch specifically for its strength and parts availability.
Ford 8-Inch
The Ford 8-inch was used in some lighter-duty F100 applications, primarily behind inline-six engines in the 1960s and early 1970s. It is visually similar to the 9-inch but smaller and less robust. The 8-inch uses a removable carrier like the 9-inch, but with smaller ring and pinion gears and 25-spline axle shafts. For stock or mildly powered trucks, the 8-inch is adequate. For anything with a V8, most builders upgrade to a 9-inch.
Dana 44
The Dana 44 appeared in some F100s during the 1960s and 1970s, primarily in 4x4 applications (both front and rear). The Dana 44 is a strong, well-proven axle used across many manufacturers (Jeep, Chevy, Dodge, and Ford all used it). It features a removable front cover for service and is available with 19-spline or 30-spline axle shafts. The Dana 44 is perfectly adequate for most street-driven F100s but does not have the same depth of Ford-specific aftermarket support as the 9-inch.
Sterling 10.25-Inch (1980—1983, Generation 7)
When Ford redesigned the rear suspension for the 1980—1983 trucks, the Sterling 10.25-inch full-floating rear axle became the standard heavy-duty option. This is a large, strong axle designed for the increased towing and payload ratings of the late-model F-Series. The 10.25 uses a rear-cover design (not a drop-out) and is identified by its large, 10-bolt rear cover. It is a capable axle but heavier than the 9-inch and with a somewhat smaller aftermarket support network.
Axle Identification
How to Identify Your Rear Axle
The fastest way to identify a Ford rear axle is by the axle tag — a small metal tag bolted to one of the differential cover bolts or attached to the housing near the axle tube. This tag contains a code that identifies the gear ratio, date of manufacture, and axle model. If the tag is missing (common on older trucks), use the following methods:
- Count the cover bolts: The Ford 9-inch has a distinctive oval-shaped removable third member accessed from the front of the housing (no rear cover with bolts). The 8-inch is similar but smaller. The Sterling 10.25 has a 10-bolt rear cover.
- Measure the ring gear diameter: Remove the cover or third member and measure across the ring gear. A 9-inch ring gear measures approximately 9 inches in diameter.
- Check axle tube diameter: The 9-inch has approximately 3-inch diameter axle tubes. The 8-inch has smaller tubes, approximately 2.5 inches.
- Look for a casting number on the center section or housing.
Axle Tag Codes
Ford axle tags typically contain a ratio code. Common codes include:
| Code | Ratio | Application Notes |
|---|---|---|
| WGE | 2.75:1 | Highway cruising, overdrive equipped |
| WGF | 3.00:1 | Common with automatic + V8 |
| WGG | 3.25:1 | Good all-around ratio |
| WGX | 3.50:1 | Popular with manual transmissions |
| WGS | 3.73:1 | Strong acceleration, towing |
| WGT | 4.11:1 | Heavy towing, off-road, 3-speed manual |
Gear Ratios: What They Mean
Gear ratio selection has a direct impact on how your truck drives:
- Numerically low ratios (2.75, 3.00) — Lower engine RPM at highway speed, better fuel economy, but slower off-the-line acceleration and reduced towing ability. Best paired with overdrive transmissions.
- Numerically high ratios (3.73, 4.11, 4.56) — Higher RPM at highway speed, stronger acceleration, better for towing and heavy loads. Best paired with 3-speed transmissions or trucks used primarily for around-town driving.
- The sweet spot for most street-driven F100s with a non-overdrive transmission is 3.50:1 to 3.73:1. For trucks with an overdrive automatic (AOD, 4R70W) or a 5-speed manual, a 3.50:1 to 4.11:1 ratio works well because the overdrive gear brings highway RPM back down.
Popular Upgrades and Swaps
Junkyard Ford 9-Inch
The most common rear axle upgrade for any F100 is sourcing a Ford 9-inch from a junkyard donor. The 9-inch was used in a vast range of Ford vehicles from the late 1950s through the 1980s, including Mustangs, Galaxies, Torinos, Broncos, Fairlanes, and Cougars. Key considerations when sourcing a junkyard 9-inch:
- Housing width: Measure the width from wheel mounting surface to wheel mounting surface. F100 widths vary by generation. You may need to narrow or widen the housing.
- Axle spline count: 28-spline or 31-spline. Upgrade to 31-spline for any performance application.
- Gear ratio: Easy to change with a third member swap.
- Bolt pattern: Must match your wheels (5 on 5.5 inches is the standard Ford truck pattern).
Crown Victoria 8.8-Inch
The Ford 8.8-inch from a 1992—2011 Crown Victoria (or similar Panther-platform car) is an increasingly popular swap. The 8.8 is lighter than the 9-inch, uses modern 31-spline axle shafts, and is available with factory limited-slip. Crown Vics are plentiful in junkyards, and the 8.8 housing width (approximately 60.25 inches) works well for many F100 applications with minor modification. The 8.8 is not quite as strong as a built 9-inch, but for a street truck making under 450 horsepower it is more than adequate and often costs less than $200 from a salvage yard.
Currie Enterprises and Moser Custom Housings
For builders who want a purpose-built solution, Currie Enterprises and Moser Engineering both manufacture custom Ford 9-inch housings built to your exact specifications — correct width, bracket placement, and axle spline count. These are the gold standard for high-performance and show-quality builds. Expect to spend $1,500—$3,500 for a complete assembly with new gears, bearings, and axle shafts.
Limited-Slip and Locking Differentials
Factory F100 rear axles were typically open differentials. Upgrading to a limited-slip (Detroit Truetrac, Eaton Posi) or locking differential (Detroit Locker, ARB Air Locker) is one of the most impactful upgrades you can make for traction. For street trucks, a Truetrac gear-driven limited-slip is the top recommendation — it is smooth, quiet, and maintenance-free. For off-road trucks, a selectable locker like the ARB gives you full lock on demand.
Parts Sources
- Currie Enterprises — Custom 9-inch housings, complete assemblies, components
- Strange Engineering — Axle shafts, spools, mini-spools, gear sets
- Moser Engineering — Custom axle assemblies, shafts, and components
- Richmond Gear — Ring and pinion gear sets
- Yukon Gear & Axle — Ring and pinion sets, install kits, carriers
- Summit Racing / Jegs — Wide selection of differential components and tools
- LMC Truck / Dennis Carpenter / NPD — Stock replacement axle components, seals, bearings
Frequently Asked Questions
What rear axle does my Ford F100 have?
Most 1957-1979 F100s have a Ford 9-inch rear axle, the most common and desirable option. Earlier 1948-1956 trucks have a banjo-style rear end. Some 1960s-1970s 4x4 models use a Dana 44. The 1980-1983 trucks use a Sterling 10.25-inch. Check for an axle tag on the housing or count the cover bolts to identify yours.
Is a Ford 9-inch rear end good for an F100?
The Ford 9-inch is widely considered the strongest production rear end ever put in a half-ton truck. Its drop-out center section makes gear changes and rebuilds far simpler than other designs. It has massive aftermarket support from Currie Enterprises, Strange Engineering, and Moser Engineering, with gear ratios from 2.75:1 to well beyond 4.56:1.
What gear ratio should I run in my F100?
For most street-driven F100s with a non-overdrive transmission, 3.50:1 to 3.73:1 is the sweet spot. Trucks with an overdrive automatic or 5-speed manual can run 3.50:1 to 4.11:1 because the overdrive gear brings highway RPM back down. Numerically lower ratios improve fuel economy while higher ratios improve acceleration and towing.
How much does a custom Ford 9-inch rear end cost?
A custom Ford 9-inch housing built to your exact specifications from Currie Enterprises or Moser Engineering runs $1,500 to $3,500 for a complete assembly with new gears, bearings, and axle shafts. A more affordable option is sourcing a junkyard 9-inch for a few hundred dollars and swapping the third member to get your desired gear ratio.
Should I add a limited-slip differential to my F100?
Adding a limited-slip differential is one of the most impactful traction upgrades for any F100. The Detroit Truetrac gear-driven limited-slip is the top recommendation for street trucks because it is smooth, quiet, and maintenance-free. For off-road trucks, a selectable locker like the ARB Air Locker provides full lock on demand.
Frequently Asked Questions
What rear axle does my Ford F100 have?
Most 1957-1979 F100s have a Ford 9-inch rear axle, the most common and desirable option. Earlier 1948-1956 trucks have a banjo-style rear end. Some 1960s-1970s 4x4 models use a Dana 44. The 1980-1983 trucks use a Sterling 10.25-inch. Check for an axle tag on the housing or count the cover bolts to identify yours.
Is a Ford 9-inch rear end good for an F100?
The Ford 9-inch is widely considered the strongest production rear end ever put in a half-ton truck. Its drop-out center section makes gear changes and rebuilds far simpler than other designs. It has massive aftermarket support from Currie Enterprises, Strange Engineering, and Moser Engineering, with gear ratios from 2.75:1 to well beyond 4.56:1.
What gear ratio should I run in my F100?
For most street-driven F100s with a non-overdrive transmission, 3.50:1 to 3.73:1 is the sweet spot. Trucks with an overdrive automatic or 5-speed manual can run 3.50:1 to 4.11:1 because the overdrive gear brings highway RPM back down. Numerically lower ratios improve fuel economy while higher ratios improve acceleration and towing.
How much does a custom Ford 9-inch rear end cost?
A custom Ford 9-inch housing built to your exact specifications from Currie Enterprises or Moser Engineering runs $1,500 to $3,500 for a complete assembly with new gears, bearings, and axle shafts. A more affordable option is sourcing a junkyard 9-inch for a few hundred dollars and swapping the third member to get your desired gear ratio.
Should I add a limited-slip differential to my F100?
Adding a limited-slip differential is one of the most impactful traction upgrades for any F100. The Detroit Truetrac gear-driven limited-slip is the top recommendation for street trucks because it is smooth, quiet, and maintenance-free. For off-road trucks, a selectable locker like the ARB Air Locker provides full lock on demand.