What type pedals does it have? If the older floor mounted "treddle type" check for accumulated dirt on the floor blocking the pedal from returning as it should. Also check linkage for dirty/rusted pivot points, weak/unhooked/broked return springs.
Some years ago I had a driver complain that Jake didn't work, brakes seemed to be dragging,& idle too high. In this case it happened to be an IHC cab-over. Handed him a screw driver & broom to clean the hardened mud from floor & a can of "loose juice" to lube the pedals. Cured the problems himself in 10 minutes.