Lock-O-Matic Hub Conversion

By Damon Gentile

So you want more than the strength of manual locking hubs and the convenience of automatic hubs ?

Try these automagic ones on for size!

This page details a quick little upgrade from the standard Jeep 6-bolt hubs to a stronger design with an added feature or two.

International Harvester Scout Dana 44 front axles run a 6-bolt hub that is compatible with the Jeep 6-bolt design.  The Jeep hub is built by Warn. IH hubs were also built by Warn, but they use the stronger 'premium' style. Of those, IH had two styles, one is a standard locking hub, and the other is known as a "Lock-O-Matic" hub. Those are the topic of this installation.

No plastic or aluminum in the IH hubs.

The Lock-O-Matic hub is outwardly very similar to a typical locking hub. However, the two positions of the dial are labeled "LOCK" and "AUTO".  These hubs have a clutch mechanism in them to engage the wheel when the axle shaft is spinning faster than the wheel. When switched into 'lock' mode they function as a typical locked hub.

The dial indicates "Lock" and "Auto"
This is a pretty simple bolt on swap, but there are a couple of things that may get you sidetracked.

The Inner hub / rotor assembly on a Jeep is typically held on by a combination of two 2+3/32 nuts and washers. The Lock-O-Matic hub uses one washer against the outer wheel bearing, a 2+3/32 nut, a special "slotted" washer, then a round outer nut.  There are at least two versions of the slotted washer, one with slots and one with round holes. Either will work.

Spindle nut washers for Lock-O-Matics

Typical Hex spindle nut, Lock-O-Matic outer spindle nut.
Take note of the holes in the surface. Arrows point to the set screws.

If you walk up to one of these in a junkyard, the round nut will be more confusing than Chinese arithmetic, so here is the secret :
There are 5 holes drilled in the face of the nut. Two are unthreaded and used for a spanner. The other 3 are threaded and they should each contain a small (5/32?") allen screw.  These screws rest in the slots in the washer, and the tab on the washer keeps the nut from rotating. Blast the grime out of the holes and back the set screws out. The round nut should unscrew easily. I made a spanner for this, starting with a spanner for a spindle on a grinding wheel and did some grinding for clearance.

The clutch of the hub rides on the outer bevel of the round nut. Also important to check is the condition of the clutch 'teeth'. They are little nylon blocks in the inboard side of the locking hub. Most that I have seen that were buggered up were from a damaged round nut.

Check this area for wear. These are nylon teeth.

Also be sure to get the snap rings that retain the hubs. IH uses a slightly different style than Jeep and the Jeep snap ring will not fit in the Lock-O-Matic hub. I fought it for about an hour before figuring it out.

Left: Jeep snap ring, Right: IH snap ring.

The installation process is very straightforward.

  1. Remove the 6 bolts around the jeep hub and remove the hub body.
  2. Remove the snap ring from the end of the axle shaft.
  3. Remove the inside portion of the locking hub from the axle shaft.
  4. Remove the outer spindle nut and washer.
  5. Install the slotted IH washer.
  6. Install the round spindle nut.
  7. Try to seat the set screws in the round spindle nut. At least two should go into the slots on the washer. If you need to move the nut to aid alignment, tighten the spindle nut.
  8. Install the inside half of the hub.
  9. Install the IH snap ring.
  10. Install the hub body and it's 6 retaining bolts. (Note that these will be 3" long for the longer body)
Road test and enjoy !

With the hubs locked, you can shift into 4-wheel drive at any time.
If the hubs are in 'auto' mode, you must come to a stop before shifting into 4-wheel drive.

If the clutch is bad (or if you don't install the round spindle nut) the clutch feature won't work in "auto" mode. However, "Lock" mode will work as a typical hub.

Also note that the hubs are strong in 'auto' mode. They are even stronger in 'lock'...

Advantages :


Text and photos copyright 2000 Damon Gentile. All rights reserved.