What is the diameter of a Ford 9 inch rear end?
The diameter most people refer to when talking about a Ford 9-Inch rear end is the ring gear's diameter, which is 9 inches in its standard form.
In practice, the 9-Inch designation describes the ring gear size used in the differential housing; builders and enthusiasts use this measurement to gauge compatibility with gears, pinions, and aftermarket components. The outside of the housing is larger than the ring gear, and the exact overall width and mounting details vary by application and year.
What the 9-Inch designation refers to
The term "9-Inch" traces to the internal ring gear that meshes with the pinion. The ring gear is 9 inches in diameter, and this dimension has been retained across most Ford 9-Inch assemblies since its introduction in the late 1950s. The function of this diameter is central to gearing options, gear ratios, and compatibility with carriers and axles that fit inside the differential case.
For performance use, mechanics pay attention to gear ratios offered with the 9-Inch family, the strength of the center section, and the spacing of the axle tubes. While the ring gear diameter stays at 9 inches, the housing width, bearing arrangement, and bolt patterns can differ between factory models and aftermarket builds.
Key facts about the diameter and its implications:
- Ring gear diameter: 9 inches (approximately 229 mm) and is the defining feature of the "9-Inch" name.
- The dimension is a reference point for gear selection and compatibility with pinions and carriers.
- The external housing width and mounting interfaces vary by model year and specification; the 9-Inch designation does not imply a single universal housing width.
In summary, the 9-Inch designation refers to the internal ring gear diameter, which is 9 inches, rather than the overall external dimensions of the axle housing.
Practical implications for builders and enthusiasts
Because the diameter is fixed at 9 inches, aftermarket gear sets and differential components are designed to fit the core measurements of the Ford 9-Inch. This standardization is part of what makes the 9-Inch a favorite in drag racing and street performance, as it simplifies sourcing parts and tuning gear ratios.
- Commonly used in a wide range of Ford models and aftermarket builds.
- Compatibility hinges on ring gear, carrier, and housing dimensions beyond the 9-inch ring gear itself.
When upgrading or rebuilding, verify the specific model's width, axle length, bearing sizes, and bolt patterns in addition to the ring gear diameter to ensure proper fitment.
Summary
The Ford 9-Inch rear end is named for its 9-inch ring gear diameter, which is the key measurement defining the axle's identity and most of its gearing compatibility. The outside housing is larger and varies by model, but the 9-inch designation remains a constant reference across generations and aftermarket builds.
How wide are Ford 9-inch rear ends?
The 9-inch rear end housings, also noted for their sturdiness, were built with case thicknesses ranging from . 150″ to . 250.” Through the years, the 9-inch was offered in seven different housing widths, from 57-1/4″ to 69-1/4″, any of which may be suitable for a particular race or street vehicle.
What is the diameter of the Dana 80 rear axle?
11.25-inch
The super-toughDana 80 rear axle ranks as one of the most desirable axles for off-highway use. It's a full-float unit with 11.25-inch ring gear diameter; 1.625-inch (minimum diameter) 37-spline pinion shaft; 11/2-inch-diameter, 35-spline axleshafts; and a 4-inch axletube diameter.
Are all Ford 9-inch rear ends the same?
We should point out there are three distinct 9-inch axle ends: the late big bearing (Torino) and the early big bearing both take a 3.150-inch od wheel bearing (the difference is in the bolt spacing for the backing plates), the small bearing ends take a 2.834 od bearing with yet a different backing plate bolt pattern.
Is a Ford 9-inch stronger than a Dana 44?
This is where our old friend the 9-inch axle comes back into the picture. A 9-inch in the rear of such a vehicle, matched with another 9-inch in front or even a Dana 44 would be just fine-strong, reliable, and not too pricey. "The 9-inch delivers the most strength per dollar," Currie told us.
