FEATURE ARTICLE from Hemmings Muscle Machines
Ford 9-inch differentials
Hemmings Muscle Machines - APRIL 1, 2007 - BY JIM O'CLAIR
It's easy to add durability and performance on a budget
About three years ago, we featured some rear axle conversions using the Ford banjo-style 9-inch differential.
Because this exchange is still one of the most popular changeovers performed by muscle car and drag racing
enthusiasts, we thought it was high time we wrote about it again. Many aftermarket rear end suppliers are now
building performance versions of the Ford 9-inch that, regardless of make, will fit just about any car or light-duty
truck. And because this differential was used as a Ford original equipment option for so many years, there are
still many used rear ends available, which can be added to your street-car or performance application with just a
few changes.
The Ford 9-inch third-member differential was first offered under 1957 Ford and Edsel models. Although not
always a sure thing, the first thing you want to look for when you are searching for one of these units is a rear
cover that does not have any bolts on it. Ford had other differentials that unbolted from the front, however, the
term 9-inch refers to the outside diameter of the ring gear and Ford's other third-member offerings has a pinion
gear that was somewhat smaller. The 9-inch ring and pinion is front-loaded into the rear end housing. First, the
pinion shaft housing is removed from the front of the housing by removing five bolts. The ring and pinion are
then accessed, also from the front, by removing another 10 bolts. Some of the 9-inch truck differentials will have
an exaggerated hump on the rear cover to accommodate the gears used in taller ring and pinion combinations.
Many enthusiasts will tell you to look for the two dimples in the rear cover to determine if the unit is a 9-inch, but
this is not always true. Ford also had an 8-inch third-member rear end that had a dimpled cover. The best test of
a 9-inch carrier is to try removing the two lower carrier case bolts. If you cannot fit a socket onto these two lower
bolts because the carrier is in the way, it's a 9-inch assembly.
The Ford 9-inch is desirable because it has a removable carrier, which allows quick rear end changes. Many
racers carry an extra carrier assembly with a different rear end ratio so they can try different combinations on
the same day while at the track. Another feature of the 9-inch third member rear end is that there are no carrier
breaks. This means you can use just about any rear end ratio you can buy without the added expense of
purchasing a larger carrier assembly for large ratios and a smaller carrier for ratios more tailored toward the
street or fuel economy. Currently there are quite a few ring and pinion combinations you can purchase between
2.50:1 and 6.50:1. Original differentials were offered with both a conventional open carrier as well as an Equa-
Lok limited slip carrier before 1972. Many of the '73-and-up pickup differentials also had a limited slip carrier
known as Traction-Lok. Although finding a limited slip rear is the best of all possible options, many aftermarket
suppliers can sell you a limited slip carrier to convert conventional units.
Ford attached an aluminum tag to one of the carrier bolts at the factory to aid in determining the gear ratio and
build date of the 9-inch rear. There are two rows of numbers on the tag. The first row will show five digits that
designate the Ford part number for the axle. The second row will have 9 or 10 digits.
First, a series of three numbers will indicate the ratio, such as 275 for 2.75:1 or 2L75 for a 2.75 positraction rear
end. The middle three numbers indicate production date and the last three digits indicate the plant code. In the
best of all worlds, you will find a differential with this tag still attached. But in many cases you will have to remove
the carrier and count the teeth of the pinion and ring gear to determine which ratio you have. We have added a
9-inch tag decoder to our technical database in the parts locator section of our Web site.
Original axles came in both 28- and 31-spline. The axles are held into the rear end housing with a flange
outboard of the axle bearing and seal. This flange is bolted to the brake backing plate. The 31-spline axles,
sought by hobbyists, are stronger and harder to find. The 28-spline rears could be easily modified to accept the
stronger 31-spline axles. Axles for these units are easily available from both salvage yards and many
aftermarket differential parts suppliers. On pre-1972 differentials it is possible to shorten the 31-spline axles to fit
narrower wheel tracks, however the 28-spline axles are tapered and cannot be shortened. Axles produced after
1972 cannot be shortened. New 28- and 31-spline axles in various lengths are available from many vendors
listed in our Hemmings publications.
You may locate an original Ford 9-inch third-member differential in one of these vehicles:
• 1957-'59 Ford station wagons, including Ranchero and sedan delivery
• 1958-'90 F-100 and F-150 pickups
• 1957-'67 Thunderbird
• 1963-'69 Falcon and Comet
• 1957-'64 Ford and Mercury full-size cars
• 1963-'69 Fairlane (note: '67 Fairlanes had coil rear springs instead of leaf)
• 1958-'60 Edsel
• 1966-'77 Bronco (uses a larger five-on-51/2-inch wheel bolt pattern)
• 1975-'78 Ford Granada and Mercury Monarch
• 1971-'76 Torino, Ranchero and Mercury Montego
• 1977-'81 Lincoln Versailles
• 1970-'79 Lincoln and Continental
• 1972-'86 E-250 Ford vans
• 1965-'73 Mustang
• 1967-'73 Cougar
There are several strength ratings for 9-inch rear ends, depending on the donor car from which they came. The
1967-'73 Mustangs used the lightest duty (thinnest tubing) 9-inch rear ends while 1957-'68 full-size passenger
cars and half-ton pickups used what is considered to be a medium-duty 9-inch differential.
The 1971-'76 Ranchero and Torino used what was considered as a race-ready, high-performance unit straight
from the factory.
The 1969-'77 full-size Ford, Mercury, Lincoln, and half-ton trucks from 1973-'86 used the strongest (thickest
tubing) rear housing of all the 9-inch rear donors. These cars and pickups are where you'll likely find a donor
differential that has the 31-spline axle configuration.
Most 1960s units were standard open rear ends; however, there were 28-spline Equa-Lok (and later 31-spline
Traction-Lok) rears used in larger engine displacements. Most of the Traction-Lok rears that you will find are in
1973-'79 pickups.
Original gear ratios covered a wide range of consumer needs. Passenger car ratios were as low as 2.50:1 and
as high as 4.11:1. Some of the truck differentials came equipped with 4.30:1 gears.
Aftermarket companies are now able to offer 38 different ring-and-pinion combinations ranging from 2.75:1 to
6.50:1, allowing you to fine tune the differential to your application.
Flange-to-flange dimensions on stock 9-inch rears range between 571/4 inches on the 1957-'59 station wagon
axles to 68 inches on the 1972 E-series Ford vans. A list of rear end dimensions is accessible through the parts
locator section of our Web site www.hemmings.com.
Probably the most popular of the 9-inch rear axle upgrades is use of the later model '77-'81 Granada, Monarch,
Versailles disc brake rear ends. This combination uses the same 9-inch rear only with original equipment rear
disc brakes already installed. These are popular with all make and model enthusiasts because these units will
install in most cars, which allow a 58½-inch-wide rear-axle wheel track underneath. Finding one of these axles is,
surprisingly enough, still not difficult. Depending on your make and model, some modification of the rear spring
mounts may be necessary, and you would also need to swap your drum-brake master cylinder for a four-wheel-
disc master cylinder and comparable proportioning valve. But, in contrast to other conversion alternatives for
adding a separate rear disc brake option, this is an economical way to go.
Before installing these units in your car, make sure to inspect the donor rear end thoroughly and change the
85W-90 gear oil and limited-slip additive if the unit is either the Equa-Lok or Traction-Lok differential. Check and
see if the rear end you have has a drain plug for removing the gear oil located on the side of the pinion carrier.
Many of the earlier housings did not and, with those units, the gear oil must be siphoned out before changing
the carrier assemblies. For servicing ease, you can add a drain plug to the lower portion of the rear cover.
Adapter U-joints are available to convert your existing driveshaft to the differential yoke on the 9-inch rear end.
Conversion U-joints can adapt even GM or Mopar driveshafts to fit a Ford 9-inch, although you probably have to
shorten your driveshaft. Because of the length of the front-loading pinion carrier, the third member assembly will
be closer to the transmission tailshaft than it normally would be with a conventional GM or Mopar differential with
a removable rear cover. This means that with the right width of axle you can transplant a Ford 9-inch into almost
any classic or muscle car. For example, at 52 inches flange to flange, you can install a 9-inch axle from a '57
Ford station wagon or a '77 Granada into a '68-'69 AMX or Javelin very easily. These same axles would also
work in a '36 to '40 Ford or a '62 Buick Skylark. Also, 9-inch rears can easily be shortened to fit your car, so if
you can't find the right width, you can still use a donor rear end that is longer than you need, but it will require a
little more work to fit it into your application. The wheel end flanges can be removed and the axle tubes can be
cut down to the proper length and the axles can be replaced with shorter units.
In checking with online salvage yards recently we found some used parts suppliers offering the Granada disc
brake rear end at $700 to $1,000, and drum brake open gear differential housings at $450 to $650. Prices for 9-
inch center sections start at $495 and increase if they are Equa-Lok, Traction-Lok, or open gear assemblies. 28-
spline axles typically sell for $100-$150 each, 31-spline axles are usually available for $150 to $200 each.
Compare these prices to the cost of purchasing an already prepared differential and you could install your own
Ford 9-inch at a savings of up to $1,000.
Ford 9-inch differentials
Hemmings Muscle Machines - APRIL 1, 2007 - BY JIM O'CLAIR
It's easy to add durability and performance on a budget
About three years ago, we featured some rear axle conversions using the Ford banjo-style 9-inch differential.
Because this exchange is still one of the most popular changeovers performed by muscle car and drag racing
enthusiasts, we thought it was high time we wrote about it again. Many aftermarket rear end suppliers are now
building performance versions of the Ford 9-inch that, regardless of make, will fit just about any car or light-duty
truck. And because this differential was used as a Ford original equipment option for so many years, there are
still many used rear ends available, which can be added to your street-car or performance application with just a
few changes.
The Ford 9-inch third-member differential was first offered under 1957 Ford and Edsel models. Although not
always a sure thing, the first thing you want to look for when you are searching for one of these units is a rear
cover that does not have any bolts on it. Ford had other differentials that unbolted from the front, however, the
term 9-inch refers to the outside diameter of the ring gear and Ford's other third-member offerings has a pinion
gear that was somewhat smaller. The 9-inch ring and pinion is front-loaded into the rear end housing. First, the
pinion shaft housing is removed from the front of the housing by removing five bolts. The ring and pinion are
then accessed, also from the front, by removing another 10 bolts. Some of the 9-inch truck differentials will have
an exaggerated hump on the rear cover to accommodate the gears used in taller ring and pinion combinations.
Many enthusiasts will tell you to look for the two dimples in the rear cover to determine if the unit is a 9-inch, but
this is not always true. Ford also had an 8-inch third-member rear end that had a dimpled cover. The best test of
a 9-inch carrier is to try removing the two lower carrier case bolts. If you cannot fit a socket onto these two lower
bolts because the carrier is in the way, it's a 9-inch assembly.
The Ford 9-inch is desirable because it has a removable carrier, which allows quick rear end changes. Many
racers carry an extra carrier assembly with a different rear end ratio so they can try different combinations on
the same day while at the track. Another feature of the 9-inch third member rear end is that there are no carrier
breaks. This means you can use just about any rear end ratio you can buy without the added expense of
purchasing a larger carrier assembly for large ratios and a smaller carrier for ratios more tailored toward the
street or fuel economy. Currently there are quite a few ring and pinion combinations you can purchase between
2.50:1 and 6.50:1. Original differentials were offered with both a conventional open carrier as well as an Equa-
Lok limited slip carrier before 1972. Many of the '73-and-up pickup differentials also had a limited slip carrier
known as Traction-Lok. Although finding a limited slip rear is the best of all possible options, many aftermarket
suppliers can sell you a limited slip carrier to convert conventional units.
Ford attached an aluminum tag to one of the carrier bolts at the factory to aid in determining the gear ratio and
build date of the 9-inch rear. There are two rows of numbers on the tag. The first row will show five digits that
designate the Ford part number for the axle. The second row will have 9 or 10 digits.
First, a series of three numbers will indicate the ratio, such as 275 for 2.75:1 or 2L75 for a 2.75 positraction rear
end. The middle three numbers indicate production date and the last three digits indicate the plant code. In the
best of all worlds, you will find a differential with this tag still attached. But in many cases you will have to remove
the carrier and count the teeth of the pinion and ring gear to determine which ratio you have. We have added a
9-inch tag decoder to our technical database in the parts locator section of our Web site.
Original axles came in both 28- and 31-spline. The axles are held into the rear end housing with a flange
outboard of the axle bearing and seal. This flange is bolted to the brake backing plate. The 31-spline axles,
sought by hobbyists, are stronger and harder to find. The 28-spline rears could be easily modified to accept the
stronger 31-spline axles. Axles for these units are easily available from both salvage yards and many
aftermarket differential parts suppliers. On pre-1972 differentials it is possible to shorten the 31-spline axles to fit
narrower wheel tracks, however the 28-spline axles are tapered and cannot be shortened. Axles produced after
1972 cannot be shortened. New 28- and 31-spline axles in various lengths are available from many vendors
listed in our Hemmings publications.
You may locate an original Ford 9-inch third-member differential in one of these vehicles:
• 1957-'59 Ford station wagons, including Ranchero and sedan delivery
• 1958-'90 F-100 and F-150 pickups
• 1957-'67 Thunderbird
• 1963-'69 Falcon and Comet
• 1957-'64 Ford and Mercury full-size cars
• 1963-'69 Fairlane (note: '67 Fairlanes had coil rear springs instead of leaf)
• 1958-'60 Edsel
• 1966-'77 Bronco (uses a larger five-on-51/2-inch wheel bolt pattern)
• 1975-'78 Ford Granada and Mercury Monarch
• 1971-'76 Torino, Ranchero and Mercury Montego
• 1977-'81 Lincoln Versailles
• 1970-'79 Lincoln and Continental
• 1972-'86 E-250 Ford vans
• 1965-'73 Mustang
• 1967-'73 Cougar
There are several strength ratings for 9-inch rear ends, depending on the donor car from which they came. The
1967-'73 Mustangs used the lightest duty (thinnest tubing) 9-inch rear ends while 1957-'68 full-size passenger
cars and half-ton pickups used what is considered to be a medium-duty 9-inch differential.
The 1971-'76 Ranchero and Torino used what was considered as a race-ready, high-performance unit straight
from the factory.
The 1969-'77 full-size Ford, Mercury, Lincoln, and half-ton trucks from 1973-'86 used the strongest (thickest
tubing) rear housing of all the 9-inch rear donors. These cars and pickups are where you'll likely find a donor
differential that has the 31-spline axle configuration.
Most 1960s units were standard open rear ends; however, there were 28-spline Equa-Lok (and later 31-spline
Traction-Lok) rears used in larger engine displacements. Most of the Traction-Lok rears that you will find are in
1973-'79 pickups.
Original gear ratios covered a wide range of consumer needs. Passenger car ratios were as low as 2.50:1 and
as high as 4.11:1. Some of the truck differentials came equipped with 4.30:1 gears.
Aftermarket companies are now able to offer 38 different ring-and-pinion combinations ranging from 2.75:1 to
6.50:1, allowing you to fine tune the differential to your application.
Flange-to-flange dimensions on stock 9-inch rears range between 571/4 inches on the 1957-'59 station wagon
axles to 68 inches on the 1972 E-series Ford vans. A list of rear end dimensions is accessible through the parts
locator section of our Web site www.hemmings.com.
Probably the most popular of the 9-inch rear axle upgrades is use of the later model '77-'81 Granada, Monarch,
Versailles disc brake rear ends. This combination uses the same 9-inch rear only with original equipment rear
disc brakes already installed. These are popular with all make and model enthusiasts because these units will
install in most cars, which allow a 58½-inch-wide rear-axle wheel track underneath. Finding one of these axles is,
surprisingly enough, still not difficult. Depending on your make and model, some modification of the rear spring
mounts may be necessary, and you would also need to swap your drum-brake master cylinder for a four-wheel-
disc master cylinder and comparable proportioning valve. But, in contrast to other conversion alternatives for
adding a separate rear disc brake option, this is an economical way to go.
Before installing these units in your car, make sure to inspect the donor rear end thoroughly and change the
85W-90 gear oil and limited-slip additive if the unit is either the Equa-Lok or Traction-Lok differential. Check and
see if the rear end you have has a drain plug for removing the gear oil located on the side of the pinion carrier.
Many of the earlier housings did not and, with those units, the gear oil must be siphoned out before changing
the carrier assemblies. For servicing ease, you can add a drain plug to the lower portion of the rear cover.
Adapter U-joints are available to convert your existing driveshaft to the differential yoke on the 9-inch rear end.
Conversion U-joints can adapt even GM or Mopar driveshafts to fit a Ford 9-inch, although you probably have to
shorten your driveshaft. Because of the length of the front-loading pinion carrier, the third member assembly will
be closer to the transmission tailshaft than it normally would be with a conventional GM or Mopar differential with
a removable rear cover. This means that with the right width of axle you can transplant a Ford 9-inch into almost
any classic or muscle car. For example, at 52 inches flange to flange, you can install a 9-inch axle from a '57
Ford station wagon or a '77 Granada into a '68-'69 AMX or Javelin very easily. These same axles would also
work in a '36 to '40 Ford or a '62 Buick Skylark. Also, 9-inch rears can easily be shortened to fit your car, so if
you can't find the right width, you can still use a donor rear end that is longer than you need, but it will require a
little more work to fit it into your application. The wheel end flanges can be removed and the axle tubes can be
cut down to the proper length and the axles can be replaced with shorter units.
In checking with online salvage yards recently we found some used parts suppliers offering the Granada disc
brake rear end at $700 to $1,000, and drum brake open gear differential housings at $450 to $650. Prices for 9-
inch center sections start at $495 and increase if they are Equa-Lok, Traction-Lok, or open gear assemblies. 28-
spline axles typically sell for $100-$150 each, 31-spline axles are usually available for $150 to $200 each.
Compare these prices to the cost of purchasing an already prepared differential and you could install your own
Ford 9-inch at a savings of up to $1,000.
| Example Ford 9-inch |