If you talk to almost anyone who is running big tires, as in more than 35 inches, they will tell you that you will need to upgrade your axles. But immediately after that, somehow the words “sixty,” “seventy,” or “fourteen bolt” usually pass their lips. Most people just automatically go to the big and heavy Dana or Corporate axles when big tires get involved. And we aren’t saying there is anything wrong with that—there isn’t.
But we wanted something lighter, and we wanted to use as many of the same parts front and rear as we could. But wait! Don’t worry! This isn’t going to be a how to build two front differentials and then install one in the rear. Let’s keep it real. No, no, instead we invested some coin in heavy-duty axles. We used a combination of low-buck and higher-dollar parts for axles whose stickers weren’t out of this world and could take on any Dana 60, 70, or 14-bolt. Plus they are lighter than the other big boys, share a lot of parts front and rear, and have a lot of commonly available parts in them, so should something blow up in the back of beyond, it will be easier to get the part and get back on the trail.
We went to Currie Enterprises for their vast 9-inch technical experience, and after explaining what it was we wanted to do and picking their brains, we came up with a plan to cook up an axle with equal parts normal and really cool that for once didn’t burn the house down.
Step By StepView Photo Gallery
1. The company talks about swedging tubes, which begins with putting the tube in lathe, truing the end of it, and then putting it in a mill to trim the face flat. That gives maximum weld area on the outside of the housing and tight fit in the centersection. Shown here is the front axle with 3⁄8-inch-wall tubes. The rear got 1⁄4-inch-wall tubes.
2. Currie has two different F9 housings. Both are similarly braced inside. This is the base model with a 3⁄8-inch-thick face. You can also see here where the tube gets welded to the inside of the housing at that circular opening. The high-zoot housing is intended for trophy trucks and is physically bigger and accepts larger-diameter axletubes. Since were already concerned about space under our Jeep and we are going to be going much slower than that, this smaller housing should be plenty for our application.
3. This third member is a real third member but it is basically a welding jig. To prevent the housing from warping or moving while welding, the third member is bolted in and the rod you can see in the previous picture is run though the slugs where the carrier bearings would be and out through slugs at the end of the tubes where the axle bearings would be.
4. After it gets tacked, the axle is then put on a rotisserie that turns at about 1 rpm.
5. After it gets tacked, the axle is then put on a rotisserie that turns at about 1 rpm. This allows the welder to make a continuous weld around the whole circumference of the tube without repositioning it.
6. Once the tubes are welded in, it was time to set the spring perches (or coil mount and control arm mounts for you coil guys). Currie has the numbers in the computer for many factory architecture applications and lift heights. Once the spring mounts are in, caster can be set and the inner “C”s welded on.
7. After the inner “C”s are welded and the tubes are welded inside the housing, it goes into this huge parts washer before heading over to the assembly area. Even though the company uses anti-spatter spray to keep finish grinding of slag to a minimum, it is best to be safe and make sure any fabrication remnant is out of the housing.
8. Because of how low this Jeep is, we saved some cash by going with a regular low-pinion centersection. A factory nodular centersection is on the right. You can see the added ribbing and thicker pinion support section on the factory nodular iron case on the left. Currie offers high-pinion iron and aluminum centersections as well which utilize a slightly smaller 8.8-inch ring gear, so Currie only recommends the high-pinion centersections for vehicles up to 400hp and 35- or 37-inch tires.
9. Since we were trying to pinch pennies, we thought a steel pinion support would be the way to go. However, Currie told us the extra material and better oiling would make aluminum a better choice for our Jeep. We also went with tried-and-true Detroit Lockers front and rear for this Jeep.
10. Currie also supplied the 5.13 ring-and-pinions front and rear. Once the ring gear has been torqued to spec using blue threadlocker and the pattern was set we opted to have the gears run-in on this dyno. The company is able to check for noise and perform the initial wear-in. Once we fill it with lube, we will have maintenance-free performance for a long time to come.
11. For the rear axle, we went with the full-floating option. If on the off chance we blow a shaft, we want to be able to pull it and limp the Jeep home on one. You can see the back side of where the brakes mount with the JK-spec wheel sensor mounts. Also notice the spindle is both butt- and rosette-welded to the tubes. The rosette weld is the telltale sign that the spindle is machined for the ID of the axletube and slips inside it about 2 inches. That makes for a much stronger end than just butt-welding it together.
12. As for those axleshafts we’ll never break (hope we didn’t just jinx ourselves), we went with the company’s cut-to-order shafts. Currie sells so many different widths and sizes of axles that to keep specific-length shafts in stock would take up 100 times the space.
13. Before you ask, no, we aren’t worried about chopping and splining a shaft. These axles are CNC induction heat treated to about 0.300-inch deep and the splines are about 0.060-inch deep. The CNC induction ensures a uniform depth and no hot spots. Factory shafts are heat treated to a depth of about 0.100-inch, so we’ve still got double the depth of any factory shaft.
14. We were also worried about the aluminum pinion support because the 9-inch has a lower pinion than even a regular Dana axle. This works well for us because we were having problems with driveshaft clearance of the high-pinion 44 front already. But the problem was that even with 40-inch-tall tires, we thought it would be grinding into rocks. Currie has released this cool pinion skidplate that perfectly mimics the F9 housing and hugs tight to the pinion. So tight, in fact, we’ve got barely 1⁄2-inch clearance around our 1350-series yoke.
15. For the front axle, we went with matching 35-spline inner and outer shafts. Currie uses late ’90s-early ’00s Ford F-450 unitbearings for strength. The company also has designed its inner and outer knuckles to accept huge 1480-series axleshaft U-joints for the ultimate in torque resistance.
16. We liked the idea of Ford unitbearings for obvious replacement reasons. However, Currie does some work on them before they go out the door. Here you can see the actual factory Ford part on the left and the Currie part on the right. Note that not only is the OD of the hub turned down, but the center hole is bigger in order to accept the larger diameter axleshaft.
17. We opted for “factory” JK brakes front and rear for all the reliability of millions of dollars of OE research. Currie cut the bolt pattern (5-on-5.5 for us) after the order was placed. In our case, the center hole also had to be opened up to accommodate our full-floating hubs.
18. Up front you can see the massive 13-inch-diameter rotor and dual-piston caliper. These brakes will require 17-inch wheels. We went with Warn Premium hubs (PN 62672) over slugs because of the Detroit Locker and because we want to drive the Jeep on the street.
19. Out back, while the factory 12.5-inch-diameter JK brakes were used, the top springs had to be swapped out for smaller diameter springs to clear the massive full-floating hubs. Stage 8 X-Lock fasteners were used to retain the hubs, and factory diameter 1⁄2-inch lug studs were used so that we could run normal Jeep lug nuts.