Jim Smart
February 6, 2015

If you’ve been messing with classic Mustangs for as long as a lot of us with graying temples, you understand how challenging it has been to find a Ford 9-inch rear with all the right parts for your early Mustang project. Used to be the Lincoln Versailles’ 9-inch axle was the hot ticket when you couldn’t find a piled up Mustang or Cougar with 9-inch cogs. And oh the times we had to take any 9-inch we could find and modify it to fit our classic Mustangs.

Currie Enterprises makes it easy to source a Ford 9-inch rearend built to your specifications because everything from flange to flange is new. Each and every 9-inch housing is assembled on site. Differential cases—cast iron and aluminum—are new. Every axle, bearing, spacer, gear, clutch, fastener, and seal is new. That said, why isn’t there a new Currie axle assembly in your classic Mustang?

We decided to visit Currie Enterprises where we met with Brian Shephard, who gave us a tour and allowed us to watch the creation of a new 9-inch axle assembly for TMI Products’ ’68 Mustang SEMA project car. This is a mild street 9-inch axle with a Traction-Lok clutch package, 28-spline axles, and 3.55 gears to go with a Modern Driveline five-speed conversion.

01. All Currie 9-inch housings are assembled in-house and given close personal attention all through the manufacturing process. When you order from Currie, you get an axle manufactured to your specifications. Because technical support is paramount at Currie, you get advice you can use when ordering and support after the sale if you run into any problems; and we challenge you to tell a Currie axle from the original.

02. Before you are new Currie parts to complement our Currie axle housing. We’re going to show you how to get a completely new Currie 9-inch axle assembly via the pieces shown here. That’s a new cast-iron “N” case accompanied by 3.55 gears, Traction-Lok clutch-style differential, bearings, seals, and all hardware. What’s more, Currie provides new 28-, 31-, or 35-spline axles, depending on your mission. Need brakes? Currie has that too for one-stop ordering.

03. Axle production begins with two 3-inch-diameter axle tubes, which are cut to the proper length per the order.

04. The axle flanges are machined in preparation for welding.

05. Axle tubes get the same treatment with this angle cut for deep weld penetration.

06. Axle assembly begins with a mockup 9-inch case for spot-on dimensions per your order. We’re building a 9-inch axle for the TMI Products Mustang show car.

07. The axle assembly is pieced together in this jig using go/no-go tooling for pinpoint accuracy. No cockeyed axle tubes or alignment issues this way. Dimensions are checked again and again because, when you weld steel, dimensions change from extreme heat. Currie welds a little at a time to prevent distortion from heat. With each weld, dimensions are checked for accuracy.

08. Dimensions are checked again prior to final welding.

09. The axle housing is completely welded before being shot blasted. Currie tumble blasts so you will receive an axle housing ready to paint.

10. Differential components are amassed and inspected before assembly begins.

11. Here, the ring gear is mated to the differential Traction-Lok clutch pack assembly, which has been assembled and checked for proper function.

12. The pinion gear and support are assembled as shown, shimmed as necessary, and checked for smooth function and resistance to rotation. Although Currie is a mass production shop, each assembly gets close personal treatment because there are no unimportant parts.

13. What makes the Currie 9-inch case better than original Ford is the abundance of iron and aluminum where it counts. Look at the iron around this pinion pilot.

14. The pinion gear and support are installed next with new seals that have been generously lubricated. Bolts are dressed with thread locker.

15. Assembly of the differential case continues with installation of the ring gear and Traction-Lok assembly. Backlash has been checked with a dial indicator.

16. Gear teeth are painted with a special coating in order to see gear mesh. Each third member is given a run through as shown to check gear mesh and listen for noise.

17. All axle shafts are new and are splined right here at Currie. Each is cut to proper length and dressed for a smooth fit.

18. Our Currie axle housing has been shot blasted and is ready for assembly. Shot blasting gives you a rough surface for good paint adhesion.

19. Each axle housing gets new seals, which are lubricated with assembly lube prior to axle installation. Seal perimeters get RTV to ensure leak-free performance.

20. The axle housing has a new third-member gasket in place and high-heat RTV added before third-member installation. Though gear lube is among the thickest lubricants out there, it always seems to find its way out. This is why Currie gets into painstaking detail with gaskets and seals. Cad-plated steel washers are used along with nylon lock nuts torqued to proper specifications.

21. Each Currie rearend gets an identification number and plate because Currie keeps a lifetime record on each component it sells. If you buy a used Currie rearend or a vehicle equipped with a Currie rearend there’s a permanent record on file of how it was built and equipped.