stuart (01/12/83)
Does anyone know what the story is about X cars and the locking brake problem? -- decvax!genradbolton!stuart
bill (01/15/83)
The information in this note is based on my knowledge of Chrysler Corporation cars and trucks from about 1962-1975; I don't know anything about the Xcars. Proportioning valves have been around on American cars [at least] since the first front disk/rear drum combinations were used. There is one primary reason: disk brakes require more force than drums for equivalent braking. I don't know of proportioning valves used on cars with four wheel drum brakes; I have no experience with four wheel disks. The disk/drum hybrids were [and are] used because it is relatively expensive to implement a conventional parking brake with four-wheel disks; the standard approach used to be to cast a drum [for parking brake only] with the rear disk, an expensive proposition. An aside: disk brakes are preferred because of their fade-resistance (due to the large braking area and superior cooling), and also because of their inherent linearity [braking as a function of pedal force]. Drum brakes are non linear because their geometry makes them "self energizing" -- the graph is concave upward. bill cox bill@uwisc ...seismo!uwvax!bill