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Nuts & Bolts: 9-Inch Front Axle

Posted in How To: Tech Qa on September 9, 2019
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I am building a Jeep Wrangler YJ with an eye towards survivability. So far I've swapped in a healthy Ford 351W V-8, an NP435 transmission, an NP205 transfer case, and a fabricated Ford 9-inch rear. I still have the Dana 30 front. I have considered a Ford 9-inch front so that I can keep a set of spare dropouts geared low with spools for fun, and a set of modest gears (3.73s) for general use. My conundrum is what to do for the outers. For fleet interchange reasons I would like to stick with the 5-on-4 1/2 bolt pattern, as they are also one of the fusible links on the build. What I mean is that U-joints and studs are cheap and easy fixes, while gears and axleshafts are not. How much tire will the Dana 30 outers handle compared to a Dana 44? I never plan on going any bigger than 35-inch tires, and then only because they are "required" for the Ultimate Adventure. Unless 34-inch Super Swamper LTBs would be acceptable? Maybe?
G.B.
Via nuts@4wor.com

You are correct in thinking that your Dana 30 front axle is living on borrowed time. With V-8 power on tap, low gearing, and 35-inch-tall tires, one stab of the throttle at the wrong time will result in bad noises and broken parts. A fabricated Ford 9-inch front axle is a good option for the reasons you state; that is, third members are easy to change if you want to swap between trail gears and street gears, not to mention a ring-and-pinion that is much stronger than what is found in a Dana 30. You also get rid of the weak center axle disconnect mechanism that is present on your Jeep's front axle.

However, if you insist on keeping your Jeep's 5-on-4 1/2 bolt pattern, you won't have many options for strength upgrades from the knuckles out over what you can upgrade with your current Dana 30. As for your fusible link theory, keep in mind that broken axle joints often take out axleshafts and break ball joints at the same time, while sheared lug studs are not an easy trail fix! And honestly, we've never heard of bolt-pattern nor lug studs referred to as a fusible link.

Unless your YJ happens to be a 1995 with ABS, the stock axleshafts use puny 5-260X U-joints, which are weaker than the 5-760X joints found in ABS-equipped YJs and 1996-later XJs, not to mention most open-knuckle Dana 44s. These same joints are also what Currie uses with its direct-replacement 9-inch front applications. It's easy enough to swap in axle stub shafts that will accept the larger 760X joints and work with your stock unit bearing wheel hubs, and these are even available in chromoly. This is a significant strength improvement, but the stub shafts are still going to be the weak link. Another option is to upgrade to an aftermarket hub conversion from Yukon Gear & Axle, which uses a stronger stub axle and has the added bonus of serviceable wheel bearings. However, the 5-on-4 1/2 hub kit uses relatively weak locking hubs like those used on Rangers and Bronco IIs for several years.

At the end of the day, having a fabricated 9-inch front axle with a 5-on-4 1/2 bolt pattern isn't much of a strength improvement because some of the weakest links from your Dana 30 will remain. Sure, there's a much larger ring-and-pinion and larger inner axleshafts with more splines, but from the knuckles out it won't be much different from even an upgraded Dana 30.

By stepping up to a 5-on-5 1/2 (or larger) bolt pattern, your strength options improve significantly. Internal spline locking hubs like those from a Dana 44 become an option, and Currie can even build a hybrid 9-inch that uses Dana 60 axleshafts and U-joints with a 5-on-5 1/2, 6-on-5 1/2, or 8-on-6 1/2 pattern. Since you want to build your Jeep with an eye toward durability, this is really a better option.

As for Ultimate Adventure requirements, 35-inch tires have always been the minimum and Editor Hazel says that rule will remain in force.

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