Umm, The major hydraulic brake difference between 1966 and 1967 Chrysler products is that the 67 has a dual master cylinder with seperate circuits. This happens to be because they went to discs up front on some cars and/or they saw the benefit of switching to dual MC's across the entire line (so far as I know). Discs require a different amount of fluid per stroke to do their work, requiring a second reservoir on the MC, and this is a safety benefit in terms of redundant circuits. However, 1967 also saw the cars that kept 4 drums equipped with dual MC as well, so this was a design decision that was seperate (and perhaps driven by) the fact that discs in front required a dual MC and THAT had its benefits. That or it was simply easier to manufacture a million dual MC and machine them for disc or drum rather than continuing to have a single MC and adding a dual as a different casting? Or it was good design sense that made for good marketing? Or some combo of the above? A proportioning valve balances two circuits out, so that brakes are applied evenly at all 4 corners, or to whatever bias you want applied (more front/more rear). Some aftermarket ones come with a knob so you can tune your own bias. The Chrysler one in particular has a retarding action on the rear circuit so that the fronts apply first and the rears come on second and to a slightly lesser degree so as to avoid rear-end lock-up in slippery conditions as the car's weight transfers forward onto the front axle. The 1966 and prior cars do not have a Proportioning Valve because they are a single pot master cylinder, and the hydraulic pressure is applied evenly on all 4 wheels. Or at least that's what I think here at work computer and not looking at my 1966 in person. I know this all because I did a sloppy job of re-assembling my 1973 rear brakes on one corner during a brake job and blamed the proportioning valve because I was so certain the rear brake shoe assy's were correct that I went after other stuff and bought a NOS Proportioning valve for $250. Hooray! The peg that goes between the shoe and the wheel cylinder was cock-eyed, so I'm now in posession of a redone brake system and a really clean proportioning valve that should last my lifetime and has the now spare original unit hanging on the wall of my workbench. ...The 63-66 drum brakes on imperials are absolutely fabulous brakes and represent the apogee of drum brake technology for large cars, I might add. -Kenyon Kenyon Wills ____________________________________________________________________________________ Never miss a thing. Make Yahoo your home page. http://www.yahoo.com/r/hs ----------------- http://www.imperialclub.com ----------------- This message was sent to you by the Imperial Mailing List. Please reply to mailing-list@xxxxxxxxxxxxxxxx and your response will be shared with everyone. Private messages (and attachments) for the Administrators should be sent to iml.webmonster@xxxxxxxxx To UN-SUBSCRIBE, go to http://imperialclub.com/unsubscribe.htm