My cadet has had these replaced, so I've never gotten a good look at the original master cylinders. I understand however that they were adapted from an automobile application (1937 Chrysler?). Is it possible the welded disc on the pushrod served a purpose when installed in the Chrysler? The type certificate data sheet does show item 307 for a parking brake at 1 lb. with an arm of -3, but I've never seen any other info on it.