Drum brakes can be grabby if the drum surface gets light rust or if the brake is cold and damp, giving the pad material greater friction. Grabbing can be so severe that the tires skid and continue to skid even when the pedal is released. Grab is the opposite of fade: when the pad friction goes up, the self-assisting nature of drum brakes causes application force to go up. If the pad friction and self-amplification are high enough, the brake stays engaged due to self-application, even when the external application force is released.
Drum brakes can be grabby if the drum surface gets light rust or if the brake is cold and damp, giving the pad material greater friction. Grabbing can be so severe that the tires skid and continue to skid even when the pedal is released. Grab is the opposite of fade: when the pad friction goes up, the self-a?ssisting nature of drum brakes causes application force to go up. If the pad friction and self-amplification are high enough, the brake stays engaged due to self-application, even when the external application force is released.