The factory front and rear diff locks (option on some 80s) have a reputation of engaging very slowly and often not at all. It's a frustrating problem which we see often. The immediate symptoms are that the front and/or rear diff lock indicator lamps on the instrument panel keep flashing.
Glen Gustafson has had a good play with the internals and here's his report (thanks Glen).
After installing a replacement rear actuator provided by the dealership where I bought my cruiser, I had time to take a look at the old one. Here is what I found:
1. The old actuator was completely filled with rusty water, including the motor housing.
2. The bleeder hose connector was completely clogged.
3. It looked like a total loss, full of corrosion mixed with remnants of white lithium grease. The motor was frozen, and the magnets came unglued from the housing when I removed the armature.
The good news is that after three evenings of cleaning it up and tinkering with it, it works great.
So... I learned that the bleeder hose may have caused the problem. It attaches to a tube that is actually bundled in the wiring harness - probably not a good idea. I'm adding a "difflock breather" of my own.
Also, the leads inside the motor are only crimped, so corrosion can ruin the connection. I soldered them.
Lastly, there are three sliding connectors inside the gear housing, so it probably can't be filled too much with grease. I'm going to try some "open gear grease", which is extremely sticky and might stay put on the gears better.
One word of caution: there are two spiral springs (like clock springs) attached to the shaft in the gearbox. It is not a good idea to try to remove those springs without special tools and a suit of armour ( I used to fix clocks). The gears and shaft can all be removed and everything cleaned up with the springs in place.
The only gear that was badly rusted was the worm gear that is part of the motor shaft. The main gear looks like plastic, and the rack and pinion are well anodized. There was also a ball bearing in the motor that was frozen, but I managed to work it free and repack it. The motor runs for such a short time I don't expect the pitted bearing will ever cause trouble.
The thing runs great on just a 9v radio battery.
BTW, there was no evidence of water in the diff oil when I changed it, and my wheel bearings are fine. The difflocks must be particularly vulnerable to water.