I'm trying to help a buddy with his 95 Ranger. It is a 4.0, 2WD, extended cab, with automatic transmission and about 260,000 miles on the clock. At low speeds, like in a parking lot or slowing to a stop, the rear brakes will sometimes lock up briefly. There is no light coming on in the instrument cluster indicating that there's a problem anywhere. I also pulled the drums off and looked inside them and everything looks good in there. Any ideas what might be causing this? I suspect something with the anti-lock system or a failing proportioning valve, but I'm hoping that maybe this is some sort of common malady that someone here might have a handle on. Thanks.