I guess they all can break. The reason I have those hubs in that picture I showed was due to one breaking, bought a new pair, broke one of those, and didn't want to keep buying pairs of hubs that cost 3x what the cheapest ones were if I was going to keep breaking them. I got some no name el cheapos from JC Whitney and those never gave a problem.
I think the problem was the automatic position is weak and should only use it for a quick engage when all it takes is getting out of the spot you're in. You know, those times when it truly is inconvenient to get out and lock them in, just to move 5' and take them back out. But I was young and had spent enough money and couldn't afford to test my theory. It makes sense, though. The Loc-O-Matics operation sticker states "For compression braking and heavy loads use manual position". In other words, when higher amounts of torque are placed on these hubs they can break. I figure the smaller parts that make the auto setting work are by-passed or tied-in solid with direct engagement. I never analyzed how they work (I should). Figure, they say the GM automatics are weak. But, for a vintage hub for a classic truck it's cool to have hubs that were ahead of their time. There was no automatic to it in 4wds. GM only started putting TH350s in trucks in '70 and warn had these hubs before GM came out with full-time 4wd. I'm sure these hubs are great in lock position, they stand out as a quality vintage accessory (although not "Hickeys"
), which gives major cool factor.
I noticed one of the Dualmatics I'm putting on my '72 isn't actuating (off the truck still). I need to break it down and see what's up. I took the other side apart to paint and just see what's up and there's not much to it. When I go to put it back together I'll see just how they function. Then I'll get into the other side. I'm wondering if I'll find what I'm seeing here in these pictures. I didn't see much of any other thing involved to break