Posted by Ken Dunnington on Monday, December 08, 2003 at 1:09PM :
In Reply to: Dual-o-Matic Hubs posted by CRW on Sunday, December 07, 2003 at 7:59PM :
Dual-O-Matic(DOM) hubs can be greased because they operate differently than other lockout hubs.
Most hubs say no grease for two reasons(or more). Turn the dial, spring pressure is exerted on the sliding gear to engage but if the splines are not lined up it will not engage. They will line up as soon as you move if they weren't in the first place. Because it's only spring pressure pushing on the gear, grease may impede it's movement when cold(ie snow...), or if excessive amounts of grease are present it may preclude full spline engagement(the gear can't fully slide into position becasue grease builds up behind it), thus weakening the connection leading to possible failure of the hub.
Now DOM hubs work very differently. The levers are attached to dowels with cut-outs on them internally that line up with a large sprocket that is riding on the axle shaft. In the disengaged position, the cut-outs allow the sprocket to turn past the dowels with no contact between them. When the barrel gets turned 180 deg to engage, the cutouts now face outward and the dowels engage the sprocket, locking the hub body to the axle shaft. When the first lever is turned, the dowel will automatically catch and line up the sprocket. Unless parts are broken internally, when you turn the lever on a DOM hub it is positively engaged/disengaged.
Neither of the bad conditions grease can cause with other hubs occurs with DOM hubs.
Thus DOM hubs can be greased. But there is no *major* metal to metal wear point inside whether engaged or disengaged. Only during operating the levers is any metal-metal wear occuring. These points are between the dowels and the sprocket(particularly the first lever to be operated), and the dowels and the hub body. Once engaged or disengaged, no parts that are touching are moving relative to one another.
DOMs are very simple hubs that work rather well. They aren't as convenient to operate as dial types, and they do allow operator error to only engage them partially(only engage one dowel of the 2,3, or 4 that are on the hub). If only one dowel is engaged, the hub is locked but will be much weaker than if properly engaged.
Sometimes the stamped "LOCK" or "FREE" are hard to read. A good way to alleviate this problem is to paint the LOCK side of each lever some bright color. When the hubs are in unlocked position, you can't see the bright paint, when locked you can. This makes for an easy visual inspection of the state of each dowel in the hub, without getting down on your hands and knees trying to read the LOCK or FREE that's filled with mud or whatever.
Lock in DOM hubs before engaging the transfer case, that way the axleshaft can be easily turned during engagement. Turning one direction vs the other when engaging may be easier. If you have a welded diff it can get difficult to engage the second side.
Ken
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