OER Parts offers a wide selection of Brake Components for your 1940 GMC Truck. OER Parts offers 1940 GMC Truck Wheel Cylinders, 1940 GMC Truck Front Wheel Cylinders 1940 GMC Truck Rear Wheel Cylinders, 1940 GMC Truck Wheel Cylinder Retainer, 1940 GMC Truck Drum Brake Bleeder Screws, 1940 GMC Truck Front Wheel Cylinder Repair Set, 1940 GMC Truck Rear Wheel Cylinder Repair Set, and 1940 GMC Truck Wheel Cylinder Pins.