Rear Brakes occasionally Lock Up

Alright this just started yesterday while out on a muddy trail and then continued intermittent the rest of the day. While even lightly applying the brake pedal the rear tires suddenly lock up and slide to a stop. This continued for the rest of the day around town and on my way home (a 90mi trip). I checked to see if any brake lines were crimped or the E-brake cable was jammed tight from a rock or unknown damage. All looks good however. It's weird and nerve racking, most of the time the brakes work fine, then all of a sudden, the rear tires are screeching to a halt. All I can really think of is the brake proportioner valve. Also the truck recently got out of the shop for gear swaps to 4.1 and a TrueTrac in the rear (Chrysler 8.25). However it was fine for the first couple of days, so not sure that it is something they did. I haven't yet pulled the drums do to lack of time but don't hear any bad noises so far. Thanks for any ideas.

if it started after you were in the mud I would suspect that your drums are full of it and causing strange behavior.

The proportioning valve should not cause the rear brakes to lock up, it only does something if there is a loss of pressure in one circuit, and if it actuates it should trip the brake warning light. Of course your year and drivetrain specs might help.

Mine did this for the first three stop signs every time it rained until I converted to rear disc brakes...pull them and clean them with water and brake cleaner, don't inhale the dust.

Even very humid weather or wet weather mine sometimes lock up on first application. I suspect its from the shoes absorbing moisture, and possibly a little out of adjustment

bcmaxx said:

Even very humid weather or wet weather mine sometimes lock up on first application. I suspect its from the shoes absorbing moisture, and possibly a little out of adjustment

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or a slight wheel cylinder leak, cause the brake fluid loves the moisture