If it's got Bendix brakes they're "self-energizing" in the forward direction. As the drum rolls forward, the motion of the drum wedges the rear shoe into the drum. In reverse, the servo action isn't as effective because the rear brake lining is longer than the front. Since the speed in reverse is usually much slower, the designers didn't make the brake self-energizing that way.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!