The Ford 9-inch Rear End

FORD 9-INCH REAR ENDS

A number of years ago, I set out to search the salvage yards in an effort to find a 9-inch rear end to go in my '68 Mustang. I knew that my up coming plans for my car were going to be way beyond anything the weak 8-inch rear end could continuously hold up to. After that first trip out to the salvage yard, I quickly realized that I didn't have a clue how to find the 9-inch rear end I needed or how to recognize it if I even saw one!
 
After re-grouping, I began a search to find materials or literature on this subject , in an effort to educate myself on what was out there, how to recoginze it, and what components I would need for the rear end to meet the demands that would be placed on it at a future date. However, a dissapointing search of past Mustang magazine issues turned up very little information there. Fortunately for me though, I had a neighbor who was the parts counter guy at the local Ford dealership (before he retired in 1999).
 
They had several very large books with all kinds of good information in them (the kind you can sit and drool over for hours at a time!) Dale, (the parts counter guy) intrusted me with the books and he would slip them to me so I could copy the information I needed out of them, and then I would return the books, before anyone noticed they were gone.
 
That was a nearly ten years ago now, when the internet was virtually unheard of. But even today, with the "information age" and all, you can still hardly find much, if any, information on this "mysterious" subject. That is why I decided to dedicate a large portion of this site to this very important component for those with a highly tweaked Mustang or Ford that are seeking to find that "elusive" 9-inch rear end to go in their street terrors, (but like me in the beginning), don't know what they are looking for. 
 

Typical 8-inch rear axle (for Mustang) vs. axle from ´57 - ´59 Ford big-car 9-inch rear end:

1. Axle on left: ´65 - ´66 Mustang - Notice "oval" area in center of axle flange.

2. Axle on right: ´57 - ´59 Ford big-car - Notice counter sunk holes in center of flange as opposed to the oval hole in the Mustang axle.

 

THE BEGINNING AND THE END OF THE FORD 9-INCH... 

The Ford 9-inch rear end made its debut in Ford half-ton pickups and in Ford/Lincoln/Mercury passenger cars in 1957. These rear ends were produced over a span of 28 years, with production ending in the Ford passenger cars at the end of 1980 and in the Ford trucks by the close of the 1985 model production run. 
The 9-inch rear end was quite possibly the all time best rear end produced by a domestic auto-manufacurer. The Ford 9-inch has a reputation for strength and a wide range of possible gear ratio applications. 
 

FORD 8 & 9-INCH REAR END COMPONENT TERMINOLOGY: 

Some times it can be confusing understanding what someone is talking about when it comes to Ford rear ends. They my say something like, "I'm looking for a Traction-Lok rear end", (meaning: whole rear end), but they may just be talking about the third member itself. Here is a breakdown of the components that make up the Ford rear end: 
 
1. REAR END: The entire (complete) rear end assembly. 
 
2. REAR END HOUSING: The foundation on which all rear end related items attach to i.e., brake assemblies, axles, and third member. 
 
3. THIRD MEMBER: The front, removable, center portion of a 8 & 9-inch rear end, which houses the differential. Also refered to as: "Pumpkin", "chunk", or "center-section". 
 
4. DIFFERENTIAL: The component responsible for directing power to the rear axle(s). It can be a Conventional style differential, (also refered to as "single track", or "open differential"). It can be a Limited-Slip, Traction-Lok, or a Detroit-Locker, and can come in either two or four-pinion arrangements (spider gears), and can have 28- or 31-spline axle gears. 
 
5. AXLES: The shafts that engage with the differential that turns the wheels to propel the vehicle. They will either be in a 28- or 31-spline configuration, in varying lengths, lug patterns, and lug spacings, as well as having large or medium axle bearing journals. 
 

1957-1959 FORD BIG-CAR 9-INCH REAR END WIDTHS & PHYSICAL DESCRIPTIONS:

The housing widths are determined by measuring from the inside of one housing end flange, to the inside of the opposite housing end flange. (this would be the flanges at the extreme ends, where the brake drum backing plates attach to the housing).
 
The 1957-1959 full-sized Ford passenger car 9-inch rear ends had a housing width of 52 ¼" across, flange-to-flange (same as 1965-1966 Mustang 8-inch rear end). These rear ends also share the same leaf-spring perch locations as the 1965-1978 Mustangs with a 43-inch distance center-to-center. (direct swap for '65-'70 Mustang [will give '67-'70 Mustangs slightly more wheel well clearance]. These "narrow" 52 ¼ housings will also fit the '71-'73 Mustangs but wider wheels & tires will be mandatory unless spacers are used with the stock wheels to space them back out.
 
The '57-'59 Ford big-car rear ends came in two housing configuration styles: (1) Large axle bearing housing. (2) Medium axle bearing housing (same bearing size as early Mustang 8-inch rear end). 
 
(1) The Large bearing housings can only be found in the '57-'59 Ford station wagons and in the '57-'59 Ford Rancheros and also in the *1960 model T-Birds.
 
(2) The Medium axle bearing housing will be found in all the other '57-'59 Ford passenger cars. 
 

PICTURES LEFT:
 
1. Housing on left: 1957 Ford Station Wagon (large bearing)
 
2. Housing in middle: 1959 Ford Fairlane (medium bearing)
 
3. Housing on right: 1960 T-Bird (large bearing)
 
Notice ´57 (left) has no dimples on rear center portion of housing. Also note 2" wide "flat band" running up center, back side of all three housings.
 
Brackets & sight/fill plug on middle housing NOT stock components. These where added to this housing.
 
Notice that left & middle housing have 3/8" NPT drain plugs in bottom of housings. No drain plug on ´60 T-Bird housing. 
 
All spring perches are 43-inch centers - same as ´65 - ´78 Mustang. Notice that perches on T-Bird housing have been relocated.
 

 

PICTURE LEFT:
 
1957 Ford Station Wagon housing width:
52 1/4 - inches (inside flange to inside flange) 
   PICTURE LEFT:
 
Notice how much thicker the perch is on the right (´60 T-Bird housing) compared to the spring perch on the left (´57 Station Wagon housing).
 
The housing to the right will automatically lower car, unless the spring perch thickness is reduced.
 
NOTE: 
Spring perch on T-Bird rear end was moved from original 36" center, to a 43" center. 
 
 

REQUIREMENTS FOR INSTALLING A 9-INCH, 1960 MODEL T-BIRD REAR END:

*The 1960 model T-Bird 9-inch rear end measures 52 ¾" inches across (that equates to ¼th of an inch, (per side), wider than the other early 9-inch rear ends, which is an insignificant amount). It also has spring perches with a distance of 36-inches apart. These spring perches have to be cut loose from the housing and moved out to a distance of 43-inches between them and then be re-welded to the axle housing tubes. Also, these '60 model T-Bird leaf-spring perches are physically much "thicker" than what is on most other Ford style rear ends. If you simply cut the perches loose and relocate them to their proper 43-inch distance, they will automatically "lower" the vehicle by nearly ½ - ¾-inch because of this added thickness, unless the "U" portion of the perch is trimmed out deeper to bring the bottom of the perch up closer to the bottom of the axle tube. 
 
The junction block, for the rear brakes, is located on the passenger's side axle tube instead of being on the driver's side like on the early Mustangs. This can easily be swapped over onto the driver's side though, and the hole left in the passenger's side axle tube can simply be welded up. 
The biggest advantage of the '60 T-Bird 9-inch rear end (once these minor modifications are made) is that this rear end has a "narrow" 52¾" large axle bearing housing, large axle bearings, large journal axles, and a huge set of rear drum brakes measuring in at 11 1/32" x 2 ½"! These drums are massive enough to stop a freight-train! 
 
 

*Stock brake line configuration. Notice the flexible brake line is located on the passenger´s side axle tube. This is the wrong side for installation in a Mustang. 
 
 
 
*Modified brake line, which moves the flexible brake line to the driver´s side axle tube. The hole that was left on the passenger´s side axle tube is welded up. 
 

PICTURE LEFT:
1960 T-Bird housing width: 52 ¾- inches
 

IDENTIFYING A LARGE AXLE BEARING HOUSING FROM A MEDIUM BEARING HOUSING:

The axle housing's bearing size can be determined (as to whether they are of the large bearing type or the medium bearing type) by looking at the holes in the housing's end flanges where the drum brake backing plates bolt up. The large bearing housings can be identified by the presence of (4) ½" backing plate bolts, while the medium bearing housings can be identified by the presence of (4) 3/8" backing plate bolts.
The ½" backing plate bolts will require the use of a ¾" socket to break the (4) backing plate retaining nuts loose with, while the 3/8" backing plate nuts will require a 9/16" socket.
 
PICTURE LEFT:
 
Flange on left is a 1957 Station Wagon large axle bearing flange w/ 3 5/32" I.D. bearing bore and w/ 1/2" dia. bolt holes.
 
Flange on right is a 1959 Ford Fairlane medium axle bearing flange w/ 2 53/64" I.D. bearing bore and w/ 3/8" dia. bolt holes.
 
BUT STEVE! there´s FIVE holes for the backing plate!?! (AHHH! but this is a "weep hole". When gear oil starts coming out of the housing through this hole, you know it's new axle seal time!) 
 
PICTURE LEFT:
 
´57 - ´59 Ford big-car rear axle comparison, medium bearing axle on the left and large bearing axle on the right.
 

EARLY ('57-'59) 9-INCH REAR END HOUSING VISUAL IDENTIFICATION: 

Looking at the backside, rear, center portion of the early 9-inch rear end housing, there will be a subtle (but noticeable) 2-inch wide "semi-flat" band running vertically up the middle. On the '57 model (only) 9-inch rear ends there won't be any dimples on the backside of the housing, but on the '58 & '59 models there will be a dimple on either side of the flat band. 
The '57 9-inch rear ends were ALL equipped with a 3/8-inch National Pipe Thread (NPT) drain plug in the bottom, center portion of the housing, while MOST '58 & '59 models had them. The '60 T-Bird rear ends didn't come with these drain plugs, but they had a fill/sight plug in the back of the housing that the previous 9-inch rear ends didn't have.
The axle tubes on these late-50s style rear ends (and the '60 T-Bird) all have 3-inch diameter tubes all the way out from the center of the housing to the flange ends, as opposed to the early Mustang's 8 & 9-inch rear ends which tapers down out toward the flange ends.  

REAR DRUM BRAKE COMPARISON:

The stock rear drum brake dimensions for a V-8 equipped Mustang measures 10" in diameter x 1 ¾" wide. The '57-'59 Ford big-car rear end's drum brakes measures 11"dia. x 2" wide. For large 9-inch axle bearing housing applications only, the drum brake size can be increased to 11" x 2¼" by pirating a rear set of drums from a '65-'67 Ford Galaxie. This will give a brake "swept area" increase of ½" over-all combined. For even more stopping power, the addition of the 1960 model T-Bird rear drums will give you a dimension of 11 1/32" x 2 ½!
NOTE: An increase in rear brake dimensions (or even when installing larger wheels & tires) should also include the installation of a manually adjustable proportioning valve, to compensate for the extra leverage. Ideally, the rear brakes should lock up just after the fronts lock up for steering controllablity reasons. 
PICTURES LEFT:
 
1 & 2. 
Ford 9-inch rear end big-car drum brake comparison. Drum on left, 1957 Ford Station Wagon 11" dia. X 2" wide. Drum on right, 1960 T-Bird 11 1/32" X 2 1/2" wide. 
 
3 & 4. 
1960 T-Bird drum brake assembly. 11 1/32" dia. X 2 1/2" wide drum. 2 1/2 " wide brake shoes. 
 
5. 
Backing plate & drum for 1960 T-Bird 9-inch large bearing housing. Drum measurements: 11 1/32" X 2 1/2" wide.
 
 

OTHER POSSIBLE DONORS FOR A 9-INCH REAR END:

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-instastalled 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: 2.47:1, 2.50:1, 2.75:1 & 3.00:1. 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. 
 
NOTE: ANY Ford 9-inch third member will fit ANY Ford 9-inch rear end housing, regardless if it was from a car or from a truck, they will all interchange as long as the 3rd member's axle gear splines match that of the rear end's axles for which the 3rd member is being installed.
 
Most passenger cars, with 9-inch rear ends, have rear end ratios commonly ranging from 2.47-3.00:1 (while there have been ratios ranging from 2.47-4.30:1).
 
The Ford half-ton trucks (with 9-inch rear ends), commonly have ratios ranging from 2.75-3.70:1 (while there have been ratios ranging from 2.75-4.57:1). There were more truck 9-inch third members with 28-splines up to 1973, than there were after 1972. The '73 and up models tend to have 31-spline third members, although there were some 28-spline third members produced for these later 70s model half-ton pickups.

REAR END HOUSING WIDTHS OF VARIOUS FORD VEHICLES: 

Measured from the inside of one axle tube end flange, to the inside of the opposite axle tube end flange --(where the brake backing plates bolt to the ends of the housing, and NOT taken from the wheel-flange-to-wheel-flange distance, --where the back of the wheel would mate up to the face of the drum/disk). 
 
1. 1965-1966 Mustang 8 & 9-inch housing width: 52¼". 
 
2. 1967-1970 Mustang 8 & 9-inch housing width: 54¼". 
 
3. 1971-1973 Mustang 8 & 9-inch housing width: 56". 
 
4. 1957-1959 Ford big-cars 9-inch housing width: 52¼". 
 
5. 1960 model T-Bird 9-inch housing width: 52¾". 
 
6. 1975-1980 Granada/Monarch 8 & 9-inch housing width: 52¼" 
 
7. 1977-1980 Lincoln Versailles 9-inch housing width: 52¼" 
 
8. *1957-1972 Ford pickup 9-inch housing width: 56" 
 
9. 1973-1979 Ford pickup 9-inch housing width: 59¾" 
 
10. 1980-1985 Ford pickup 9-inch housing width:?? 
 
11. 1966-1977 Ford Bronco housing width: 52¼" 
 
12. 1978-1985 Ford Bronco housing width:?? 
 
* The 1972, and earlier, Ford half-ton pickup's 9-inch rear end could be used in the '71-'73 Mustangs, (if no suitable donor from a car can be found), if some modifications to the rear end housing, brake drums, and lug spacings were made: 
 
1. The spring perches would have to be moved from the the top of the truck's axle housing tubes to the underside of the tubes, and placed at the correct 43-inch distance apart. 
 
2. The truck's brake drums would have to be re-drilled to the correct 4½" lug spacing to fit the '71-'73 Mustang's pattern. 
 
3 The axleshaft's wheel flanges would also have to be re-drilled to accommodate the 4½" lug spacing. 
 
4. For better appearances, the lower shock mounting brackets would also need to be removed from the Ford truck's 9-inch rear end housing tubes. 
 
(** Similar modifications would apply to '66-'77 Ford Bronco 9-inch rear ends, to install in the pre-'71 Mustangs).  
 

FORD REAR END WEIGHT COMPARISON

8-inch Rear End Assembly Weight : 170 lbs.
 
1. Housing: 36 lbs.
 
2. Axles: Medium Journal, 28-spline -15 lbs. ea.
 
3. Brakes: Small 10" x 1¾" Drum Assemblies - 22 lbs. ea.
 
4. 3rd Member: Reinforced Revision 8-inch Case - 60 lbs.
 
 
 
 
9-inch Rear End Assembly Weight: 194 lbs.
 
1. Housing: 38 lbs.
 
2. Axles: Large Journal, 28-spline - 18 Lbs. ea.
 
3. Brakes: Massive 11-1/32 x 2½" Drum Assemblies - 26 lbs. ea.
 
4. 3rd Member: Conventional Diff. - 68 lbs.
a. w/Traction-Lok Diff. - 71 lbs.
 
(24 lbs. Difference Between Drum Brake 8" & Drum Brake 9" Rear End Assembly).
 
 
 
 
Versailles Disc Brake Rear End Assembly Weight: 215 lbs.
 
1. Housing: 39 lbs.
 
2. Caliper: w/Pads, Anchor Plate & Flexible Brake Hose - 24 lbs. ea.
 
3. Axles: 20 lbs. ea.
 
4. Rotors: 10 lbs. ea.
 
5. 3rd member: Conventional Diff. - 68 lbs.
 
(45 lbs. Difference Between Drum Brake 8" & Disc Brake 9" Versailles).
 
 
 
 
Wheel/Tire Comparison:
 
1. Stock '66 Mustang GT Styled Steel Wheel w/ P195/70R-14 Tire - 46 lbs. ea.
 
2. Weld Draglite Forged Aluminum Wheel (15" x 8") w/ P245/60-15 Tire - 38 lbs. ea.
 
 
 
 
Miscellaneous:
 
1. 8" Drum Brake Assembly: (10" x 1¾" Drums): 22 lbs. ea.
 
2. 9" Drum Brake Assembly (11-1/32" x 2½" Drums): 26 lbs. ea. 
 
3. Lincoln Versailles Disc Brake Assembly: (10½" Rotors) 30 lbs. ea.
 
4. Lincoln Mk VII Rear Disc Brake Rotor/Caliper Assembly Weight: (11¼" Rotors) 22 lbs.ea.
 
5. Ford Explorer Rear Disc Brake Rotor/Caliper Assembly Weight: (11¼" Rotors) 25 lbs. ea.