Here's some good info if your looking to replace factory diff with a ford 9"
No guarantee as to the accuracy of this data.
Year & Model
Axle Length
Notes
1965-1966 Mustang 57.25 inches
1967-1970 Mustang 59.25 inches
1971-1973 Mustang 61.25 inches
1977-1981 Versailles 58.50 inches
1967-1973 Mustang, Torino, Ranchero, Fairlane 59.25 inches to
61.25 inches
1957-1959 Ranchero and station wagon 57.25 inches
1966-1977 Bronco 58 inches
1977-1981 Granada/Versailles 58 inches
1967-1971 Comet, Cougar, Mustang, Fairlane 59.25 inches
1971-1973 Mustang 61.25 inches
1964 Falcon 58 inches
1967 Cougar 60 inches
1967 Fairlane 63.50 inches coil springs
1972 Ford Van 3/4 ton 68 inches
1973-1986 Ford Van 3/4 ton 65.25 inches
1957-1959 Ranchero and station wagon
57.25 inches
narrowest 9" housing
1966-1977 Bronco 58 inches 5-on-5 1/2 inch diameter bolt circle
1967-1973 Torinos, Rancheros, Fairlanes 59.25 inches or
61.25 inches
1967-1971 Comets, Cougars, Fairlanes 59.25 inches
1975 Mustang II 8" 57.00 inches
1974 Maverick 8" 56.50 inches
Where To Find The Nine Inch Rear Axle
1967-1973 medium and big block Mustangs and Cougars 1966-1971 Fairlanes, Torinos, Montegos, Comets, and other Ford intermediates with big blocks.
1957-1959 V8 Fords and Mercurys
1977-1981 Lincoln Versailles & Trucks
Types Of Nine Inch Axle Housings
1967-1973 Mustang/Cougar - light duty, thinnest housing material, small axle bearings, 28 and 31 splines.
1957-1968 passenger car and 1/2 ton truck - medium duty, stronger than Mustang type, 28 and 31 splines.
Ranchero/Torino - heavy duty thick wall housing, 3.25 inch diameter axle tubes with flat tops.
1969-1977 Galaxies (coils), Lincolns (coils), and late pickups (leaf)- 3.25 inch diameter all the way to the backing plate, coil housings have upper control arm mount
How To Recognize Nine Inch Housing Centers
1957 - no dimples, flat center band up the center of the rear cover, bottom drain plug.
1958-1959 - two dimples on back of housing, flat center band, some had drain holes.
1960-1967 - two dimples, flat center band, oil level hole in back cover.
1963-1977 Lincoln, LTD, Thunderbirds had 9.375 inch centers, housings were cut away at the gasket surface for ring gear clearance, one curved rib at the front top portion of differential, strong but no gears.
Tip On Shortening Nine Inch Axles
1972 and earlier 31 spline axles have the ability to be shortened.
28 spline axles are tapered and cannot be shortened and re-splined.
1973 and later cars have a 5-on-5 bolt circle and the axles cannot be shortened.
1967-1973 Mustang axles can be identified by wheel flange:
Oval hole = 28 splines.
Two large holes and counter-sunk center = 31 splines.
