94 b250 van brake lockup??

Hi, My dad has a 94 B250(I think!) van that he claims the brakes both locked up on the freeway. He said both were smoking when he came to a stop. He did try greasing
the slides, but said the same problem...brakes stuck when applied.
Question, what could it be? ABS? master cylinder? or brake calipers. Van has only 70k miles but the fluid was changed once a few years ago.
I've read other posts that it maybe the master or brake calipers, how can I isolate that?
Thanks for any suggestions.
-joe
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Both? There's four... which both?

Okay - so we're talking the fronts...

My first guess? Deteriorated rubber brake hoses that aren't letting the pressure out of the calipers when the pedal is released. Simple test: Stand on the brakes, let off, then open up a bleeder screw. If fluid squirts out of the bleeder like a Super Soaker, then that's your problem.

Should be done every 2 years...

A sticking caliper won't usually cause a wheel to lock up like that... cause the vehicle to pull, or to wear out pads faster, sure. As for testing the master cylinder, you can use the same principle as above (and actually, you should do this first) - pump the brakes, let off the pedal, then back off the line nut that connects the front brake line into the master cylinder. If fluid shoots out under pressure, then the master cylinder has got a problem. If it only dribbles out, then repeat the test at the caliper bleeder.
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