The right main gear collapsed on landing. Investigation revealed that the rear trunnion pivot pin, P/N5741112-1, had moved aft and out of the trunnion. The pin had about 1 inch of white paint on the end of the pin that extended into the flap track area. The extension of the rear pivot pin on the left gear was measured at 1/2 inch of painted pin extending into the flap track area. The pivot pin is held in the trunnion with a roll pin. The aft pin still had a section of the roll pin in it and the failure mode was a shear. The other two small pieces of the roll pin were still in the trunnion. The forward pivot pin showed a wear pattern that the shims had been riding about 2/10 inch further from the pivot pin hole than on the rear pin. Additionally, the rear pin had grooved wear marks all the way to the end of the pivot pin from the point of original wear pattern.