1979-1989 GMC P2500. Notes: Drum Brake Wheel Cylinder -- 11.15 In. x 2.75 In. Brakes; Bore: 1 In. Specifically engineered to be direct match for original drum brake wheel cylinder. Position: Rear. Ensure Proper FitTo confirm that this part fits your vehicle, enter your vehicle's Year, Make, Model, Trim and Engine in the Compatibility Table.