What Master Cylinder is required to handle rear disk brakes?
CarQuest #20-1583 (1972 to 1976 P-30 with 15″ drums and 4″ shoes) modified 3-11/16″ long pushrod I had reported earlier that my Cinnabar master cylinder with less than 10,000 miles on it failed here in Florida. Jim Bounds had a brake mechanic look at it and they indicated that the GMC original master cylinder just didn’t have enough capacity to handle the four wheel calipers that I had put on with the StreetRod disk brake kits. They felt that most of my braking was from the front brakes (80 mm calipers). My thanks to several who posted that I should use the P-30 chassis master cylinder which has a 1-1/4″ bore. I was told that Leigh Harrison uses this cylinder with his brake kits. The mechanic tried this and still wasn’t satisfied with the amount of pedal. He then put on a 1-5/16″ bore cylinder which was CarQuest part number 20-1583. (CarQuest has three master cylinders listed for P-30. The Part number 20-1583 is for a 1972 to 1976 P-30 with 15″ drums and 4″ wide brake shoes. The other
