From: utzoo!decvax!harpo!seismo!hao!cires!harkins Newsgroups: net.auto Title: brakes Article-I.D.: cires.1974 Posted: Wed Jan 19 09:50:48 1983 Received: Mon Jan 24 01:16:56 1983 bill cox is right: the proportioning valve appeared with the disc/drum combo; the locking up type situation is what demanded their use in the first place; gm just did a lousy job of engineering i'd say and/or they used a valve designed for a different weight distribution than the x-cars happened to have ernie harkins