Remember the days of scrounging junkyards in search of a 9-inch rearend to replace the wimpy 8-inch in your high-horsepower vintage Mustang? Whether you were looking to beef-up the strength for hard launches or you desired a higher (numerically) gear ratio, the 9-inch from an old Galaxie, truck, or - if you were lucky - a high-performance Mustang got you both strength and, more than likely, a digger gear. Today, it's virtually impossible to find an old 9-inch in the junkyard.
That's one reason that John's Industries, home of The 9-inch Factory, offers a bolt-in Sport 9-inch rearend for '65-'73 Mustangs and other vintage cars. With brand-new housings made from The 9-inch Factory's own tooling, the rearend assembly comes with your choice of Motive ring-and-pinion gears in a lightweight nodular case, Traction-Lok differential, OEM 28- or 31-spline axles, and big-bearing, late Torino-style flanges. To help with the swap, the housing is also fitted with spring perches, brackets and tabs, new pinion yoke, axle seals, studs, fasteners, and housing vent. Available options include 10x21/2-inch drum brakes, aluminum third member, pre-bent brake lines, and disc brakes from either Ford Racing or Stainless Steel Brakes Corporation.
The Sport 9-inch arrived at...
The Sport 9-inch arrived at Classic Creations of Central Florida with everything needed to swap from an 8-inch rearend to a stout 9-inch in Brett Butler's '65 Mustang. It's equipped with 3.50 Traction-Lok gears and 10 1/2-inch drum brakes. Black powdercoating provides a more durable factory-look finish.
With prices starting at just under $3,000 retail for a unit with drum brakes, the bolt-in 9-inch rears aren't cheap. And the price goes higher when you add disc brakes, powder coating, and other options. However, when you look at it as a complete, ready-to-swap assembly that provides better brakes, a beefier housing, and Traction-Lok gears of your choice, it's a pretty good deal compared to locating a suitable vintage 9-inch and adding all the components yourself.
The 9-inch factory sent us a bolt-in Sport 9-inch for Classic Creations of Central Florida customer Brett Butler, who was looking for a 9-inch and gear ratio upgrade to replace his '65 Mustang fastback's original 8-inch, which was leaking fluid and whining at highway speeds. Merv Rego and Matt Simmons, with help from Brett, made the rearend swap in an afternoon, with only a couple of modifications required - a different universal joint to mate to Brett's driveshaft and some minor grinding to open up the spring perch positioning hole for Brett's lowering blocks. Wider u-bolts and shock/spring mounts from '67-'70 Mustangs are also required.
 With The 9-inch Factory's...  With The 9-inch Factory's optional pre-bent brakes lines, the 9-inch is a straight bolt-in for most '65-'73 Mustangs. |  With The 9-inch Factory's...  With The 9-inch Factory's bolt-in rearend, the 8- to 9-inch swap is pretty much a remove and replace procedure. With the car raised and supported by sturdy jack stands at the rear frame rails in front of the rearend, yank the wheels and, if the 8-inch is equipped with factory-style drum brakes, pull the drums to access the emergency brake cables. Disassemble the brakes to release the cable on each side and pull them through the backing plates. |  |
 Everything connected to the...  Everything connected to the rearend needs to be unbolted or disconnected, including the driveshaft at the universal joint, vent hose, brake lines, and rear shocks. Then support the rearend with a floor jack and remove the u-bolts that attach the housing to the leaf springs. In this case, the u-bolts were longer than stock due to Brett's use of lowering blocks. |  With the rearend supported...  With the rearend supported securely by the floor jack, remove the rear shackle bolts to release the rear of the leaf springs. These bolts can be stubborn, especially if they're rusty. You may need liberal amounts of penetrating lubricant. |  With helpers on each side...  With helpers on each side to balance the rearend on the jack, carefully lower the housing and roll it from under the car on the floor jack. |
 Matt Simmons had the forethought...  Matt Simmons had the forethought to check the fitment of Brett's lowering blocks to the 9-inch spring perches. He discovered that the positioning holes were too small. |  Matt used a drill with a rotary...  Matt used a drill with a rotary file to open up the spring perch positioning holes to fit the lowering blocks. |  A trial fit of Brett's driveshaft...  A trial fit of Brett's driveshaft to the 9-inch rearend yoke revealed that we needed larger universal joint bearings and caps, located at a local auto parts supply store. Because there are so many variables for Mustang driveshafts, yokes, and u-joints, especially after cars have been modified and repaired over the years, you can expect to find the same situation on your Mustang. |
 Before installing the 9-inch,...  Before installing the 9-inch, we pulled a drum to compare the brake linings. As you can see, the 101/2-inch drums on The 9-inch Factory's rearend offer much more surface area than the stock brakes on an 8-inch rear. | | |