All 4 brakes locked up at once

So, interesting development. I started the truck up, ran it forward, reverse, 2wd, 4wd. All of those will move the appropriate wheels. I pumped the brakes to try to get them to lock up again and checked how hard it was to spin the tires, no change. Turned the truck off, pumped the brakes until the pedal completely stiffened up and there was also no change in how hard it was to turn the tires. As of now, grabbing the outer lug and spinning them as hard as I can, I get about 1 revolution out of them. It seems the brakes aren't locking up anymore, just partially applied. I'll still give cracking the nuts a shot, but just thought I should add this.

 

So I just rechecked all the brake line nuts and none of them seem to be pressurized. The horizontal ones on the MC and ABS module leaked a little out, but it was just slow leakage. The ones that came up vertically out of the ABS module didn't leak at all. These were all loosened 3 to 4 turns to the point where I could wiggle the lines around. Does this mean the MC/ABS module aren't the culprits?

 

If your brakes were still locked up after doing that then no it doesn't sound like it.

 

That's kind of a relief, because I'll be much more comfortable messing with the calipers or putting new ones on if I have to. Thanks for all the insight, and if anything I learned a new skill. I really appreciate the help.

 

Well, I'm stumped. The brakes don't seem to be locking up anymore. The MC, ABS module, and bleeder valves weren't under excessive pressure, and the pistons were easily compressed with pliers. All tires seem to turn on idle at least on jack stands despite there being no gap between the pads and rotors. And the kicker, the brake lights shut off with the brake pedal plug reconnected, so they work as intended now. I'll take it for a spin around town tomorrow to see if anything happens. Just so I know when I go to check it after driving around tomorrow, what size gap should there be between the pads and the rotor? I assume there is supposed to be some gap, but that's never really been something I payed any attention to. Maybe I got lucky and it's a case of take it apart and put it back together again.

 

Yea I hate intermittent's, they can be a real pain to diagnose. Really without catching it acting up, there's no way to tell what's bad.

 

Well I got the tires back on and took it for a test drive with the ABS #2 fuse removed for good measure and everything seems normal. Pedal feels fine, doesn't feel like the truck is dragging or anything. I wonder if the ABS module just overheated and locked up yesterday and maybe it cooled down by the time I started messing with everything. I really aught to put in a switch or something to disable the abs on demand. I'm sure it's great and all under normal conditions (never needed it before), but during winter if I'm on snow or ice, the truck refuses to let me stop when going at low speeds in parking lots or the last couple feet of coming to a stop in street traffic.
I'll be careful driving around for a little while, but hopefully this was just some hiccup.