Hubs & Axle Vacuum Disconnect BasicsPosted in How To: Transmission Drivetrain on March 1, 2011
While standing around kicking the concrete and shooting the breeze one day at T&J Performance Center in Orange, California, we got to talking about easy fixes. Some folks are wasting their hard-earned money because they're intimidated or too lazy to fix minor mechanical issues. It should be a rule of owning a Jeep that some of its repairs and upgrades be completed by the titleholder. Not knowing how to fix easily repairable mechanical problems out on the trail can lead to major problems. So get familiar with your rig and fix those headaches before they turn into disasters.
A good example of an easy repair/ upgrade is the replacement of the manual locking hubs and fixing the problematic vacuum-actuated axle locking system on the Dana 30 front axle. So what do manual locking hubs do? Locked hubs give the Jeep its four-wheel-drive traction by locking the front wheels to the axleshafts so they'll turn from the power of the transfer case when it's shifted into 4-Hi or 4-Lo. When the hubs are unlocked the wheel spins independently of the axleshafts and differential. Leaving a broken hub on the axle shouldn't hinder progress, and the rig may be able to make it back to the trailhead. However, a broken hub limits the Jeep's traction. If the rig is stuck in a tough situation, replacing or repairing the hub will likely allow the Jeep to drive out of it.
The Dana 25, 27, 30, and 44 Jeep axles have manual locking hubs and/or nonserviceable unit bearing hubs, and some use a vacuum-actuated axle lock. Most manual locking hubs are comparable in design and can be repaired, replaced, or retrofitted in a similar manner. Aftermarket hubs and their internal parts vary slightly but can all be installed and repaired using basic tools.
The Dana 30 under the Wrangler YJ, early Cherokee XJ, and Comanche MJ doesn't have manual locking hubs, but instead uses a vacuum-actuated central axle disconnect (CAD) system located on the passenger side of the housing. The system consists of a two-piece splined shaft and a coupler that slides back and forth by a vacuum-operated shift fork. The action of the fork either connects or disconnects the shafts. The dubious system uses a vacuum motor that can seize and rubber lines that rot.
The whole system can be replaced by a manual hub conversion kit, but such kits are a bit pricy. Just a few hundred bucks more (not counting installation) can get a larger and complete axle, such as a JK Rubicon axle complete with locker.
An economical fix is the 4x4 Posi-Lok system, or you can get locking hubs and a passenger-side axle assembly from a nondisconnect Dana 30 and slide in a new inner axle seal that fits inside the differential. Both the manual locking hubs and the 4x4 Posi-Lok are easy fixes that can be completed under an hour each.