Ford Rearend ID and info


Ford Rearend ID and Info

Housing widths are measured from the the flanges where the drum brake backing plates attach to the rear end housing ends, and not where the back of the wheel mates up to the face of the brake drum surfaces.

  • 1965-1966 Mustang 8 and 9-inch housing width: 52 1/4- inch
  • 1967-1970 Mustang 8 and 9-inch housing width: 54 1/4- inch
  • 1971-1973 Mustang 8 and 9-inch housing width: 56- inch
  • 52 1/4  In 1974, the Mustangs only rear end choice (with a drop-out style
    third member), was the 8-inch (no more 9’s). The housing widths for these Mustangs dropped back to the original housing width. The only kicker here is that they are equipped with 4-lug axles and not with 5-lugs. To convert these housings to a 5-lug setup, you will have to have axles from a pre-’67 Mustang, or related Ford.
  • 1957-1959 Ford big-cars 9-inch housing width: 52 1/4- inch
  • 1960 model T-Bird 9-inch housing width: 52 3/4- inch
  • 1975-1980 Granada/Monarch 8 and 9-inch housing width: 52 1/4- inch
  • 1977-1980 Lincoln Versailles 9-inch housing width: 52 1/4- inch
  • *1957-1972 Ford pickup 9-inch housing width: 56 inch
  • 1973-1979 Ford pickup 9-inch housing width: 59 3/4 inch
  • 1980-1985 Ford pickup 9-inch housing width:??
  • 1966-1977 Ford Bronco housing width: 52 1/4 inch
  • 1978-1985 Ford Bronco housing width:??

Strength – There are four usable styles you will find.

They range from light duty to extreme duty but in all cases the larger 31 spline axle
versions are stronger than the 28 spline version of the same unit.

Light duty
The 67-73 Mustang type is considered light duty uses both axles.
Medium duty
The 57-68 early passenger car and half-ton pickup rear end is considered a medium duty unit and came in both 28 and 31 spline axles.
High Performance
The 70-79 Ranchero/Torino are considered a high performance unit again being produced with both 28 and 31 spline axles.
Extreme Duty
The 69-77 Galaxie/Lincoln and 73-86 half-ton pickup used both size axles and the 31 spline
version should be considered the strongest available and can be used for extreme

If you use the 57-72 F100 rearend, if you use the driver’s side axle, backing plate, and
drum from a 72-79 Torino, Ranchero, LTD II or 77-79 T-bird or Cougar, they will swap into the truck housing. That will give you 4 1/2 inch bolt pattern

The 1975-1980 model Granadas and Mercury Monarchs came equipped mostly with 8-inch rear ends. Some were also equipped with an 8.7-inch rear end –identifiable by a removeable rear cover (not desirable). Some models also had drum brake equipped 9-inch rear ends while a few had the optional 9-inch rear ends with factory-installed disk brakes.

The 1977-1980 Lincoln Versailles came standard with the 9-inch disk brake rear end. However, there are only four ratios to be had with any of these rear ends. They are: 2.47 / 2.50 / 2.75 / 3.00. Good for gas mileage purposes, but not good from a performance stand-point.

Most of these 9-inch 3rd members came as a Conventional (single track) 3rd member. Some had two pinion (spider gears) Traction-Lok differentials, while some had the stronger four pinion Traction-Lok differentials.


You must have an axle housing with Large Axle Bearings.

You must have a housing with 3/8 inch diameter flange bolts at the housing ends (NOT the inch diameter flange bolts found on some housings), and the bolt spacing pattern has
to be 2-inches vertically x 3.56-inch horizontally (NOT 2-3/8 inch vertically X 3.56 inch

The distance from the wheel surface of the axle flange to the start of the axle bearing
journal surface has to be a minimum distance of 2.188 inch.

NOTE 1: Mustang 8 and 9 inch rear ends have Medium Axle Bearing Housings, and most of their axles fall in the 2.090-inch range. So in other words, if you have a Mustang 8-inch
rear end, or if you have a 9-inch rear end with Medium Axle bearings, you’re pretty much
outta luck on this swap.

NOTE 2: there are also two different versions of the Versilles rear end housing. Both have
the Large Axle Bearings, but one has 1/2- inch diameter end flange bolts on a 2-3/8-inch x
3.56- inch hole pattern, while the other has 3/8-inch flange bolts also on a 2-3/8-inch x
3.56 – inch hole pattern. While the Explorer rear discs will work on these rear end housings, it will take some modifications to make it work.


  • 8-inch Rear End Assembly Weight : 170 lbs.
  • Housing: 36 lbs.
  • Axles: Medium Journal, 28-spline -15 lbs. ea.
  • Brakes: Small 10 x 1 3/4 – inch Drum Assemblies – 22 lbs. ea.
  • 3rd Member: Reinforced Revision 8-inch Case – 60 lbs.
  • 9-inch Rear End Assembly Weight: 194 lbs.
  • Housing: 38 lbs
  • Axles: Large Journal, 28-spline – 18 Lbs. ea.
  • Brakes: Massive 11-1/32 x 2 1/2 – inch Drum Assemblies – 26 lbs. ea
  • 3rd Member: Conventional Diff. – 68 lbs
  • w/Traction-Lok Diff. – 71 lbs
  • 24 lbs. Difference Between Drum Brake 8 and Drum Brake 9 Rear End Assembly
  • Versailles Disc Brake Rear End Assembly Weight: 215 lbs .
  • Housing: 39 lbs
  • Caliper: w/Pads, Anchor Plate and Flexible Brake Hose – 24 lbs. ea
  • Axles: 20 lbs. ea.
  • Rotors: 10 lbs. ea.
  • 3rd member: Conventional Diff. – 68 lbs.
  • 45 lbs. Difference Between Drum Brake 8 and Disc Brake 9 Versailles
  • Wheel/Tire Comparison:
  • Stock 66 Mustang GT Styled Steel Wheel w/ P195/70R-14 Tire – 46 lbs. ea.
  • Weld Draglite Forged Aluminum Wheel (15 x 8) w/ P245/60-15 Tire – 38 lbs. ea.
  • Miscellaneous:
  • 8 -inch Drum Brake Assembly: (10 x 1 3/4 Drums): 22 lbs. ea.
  • 9 -inch Drum Brake Assembly (11-1/32 x 2 1/2 Drums): 26 lbs. ea.
  • Lincoln Versailles Disc Brake Assembly: (10 1/2 – inch Rotors) 30 lbs. ea.
  • Lincoln Mk VII Rear Disc Brake Rotor/Caliper Assembly Weight: (11 1/4 -inch Rotors) 22 lbs.ea.
  • Ford Explorer Rear Disc Brake Rotor/Caliper Assembly Weight: (11and 1/4 -inch Rotors) 25 lbs. ea.

Rear End Ratio Selection

We are not talking economy here, just performance. For a street car to be a strong
performer, you need a torque multiplication ratio of at least 9:1. To figure this, multiply the
transmission’s first gear ratio by the rear end’s ring and pinion ratio. A C4 has a first gear
ratio of 2.46:1. An AOD has a first gear ratio of 2.40:1.

Example 1) 2.46 X 3.00 = 7.38 Torque multiplication ratio.

Example 2) 2.40 X 3.89 = 9.336 Torque multiplication ratio. (MUCH better!) A Mustang with 26
– inch tall tires, non-overdrive trans (1:1 in high gear), 3.00:1 rear end ratio, and traveling
@ 60 MPH, will be turning roughly 2,326 RPM. Given the same circumstances except for a AOD transmission change (0.68:1 in overdrive), and 3.89:1 rear end gears, the same vehicle would be turning 2,051 Rpm’s!


5 thoughts on “Ford Rearend ID and info

  1. Clarke Pringle

    I have an 8 inch housing that measures 51 1/4″ flange to flange, 5 lug, 3.55 gear ratio (could be aftermarket) and 10″ X 1 3/4″ rear brakes. Any idea what it came out from under?

  2. Lindsay Bennett

    I just got my Marti report back on a 71 mach 1. I just needed to know that the 3 speed manual tranny was original. And it is. Now the other thing is, I have a 3.00 traction lock rear end. Now would that be a 8 inch or 9 inch? It has a 351c 2v. Do you know what size the rear end is? Thanks

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