[Chrysler300] RE: Re; Caliper retraction measurement procedure

Thanks Jim,..great input.

I have been thinking a lot about this..if it knocks back, as they do and is accepted to some degree, it is still ok if a single stroke of master cylinder can still apply the brakes—by filling the “new” dead space created, ( which it never had to deal with before) ---possibly at all 4 wheels .The means only a pedal drop if master itself displaces enough cc.. That says big bore long stroke master which also usually says power brakes. (or very hard pedal, you cannot have big volume by a bore increase, and easy / same pedal force) The corvette master is a common choice here. I used it in my hemi Studebaker, (see Turner Brake Kit for studes—good info) , no power , it was still OK, which is counter to what follows. Maybe a light car and aggressive old Studebaker manual pedal ratio (underfloor mount) .

Also I think the F I am working on, the brake kit I bought has that master, or one like it. Corvettes must have had to sort this out, w 4 wheel discs. It simply cannot happen as much with drums, adjuster limits back stroke, so nothing extra in cc ability is required to deal with it at master. There is a chance that multi puck per wheel systems have more cc volume to fill , with many more pucks knocked back, but not sure of that . Guys with Dart probably left the stock mopar master, designed for smaller pucks, stock master could not fill the volume of Wilwoods on one first push, after knockback.= no brakes until second push. Or if they changed master, the choice they made was wrong. . Possibly related to all this is the anti flow back or check valve, which might not have been properly applied? I think they have external 5 psi and 15psi available..and sometimes internal. That tradeoff is being hard to knock back in first place, against 5 or 15 psi in the puck, trade against constant brake drag, but seems absolutely a requirement on discs (for just keeping puck reasonably near disc if nothing else) . But on previously mentioned 80 Dodge truck, and some JEEP GC 97- 03 at least, it causes or initiates actual burning of the shoe and locking on (only!) one front..each of those vehicles did that nice thing to me. In heavy slow traffic jam , of course,--- disc gets hot with constant stop and go for 30 minutes, expands , starts dragging a bit, gets even hotter, away we go, big smoke, burn and lock. ( by the way apply hard backing up seems to free it—easy on a freeway)

While a long story, the extreme details are too long for here, I found out (with help from J-Y) there are truly major changes in pedal arm to master ratio (almost twice!) ,and master mount height in 1960 Mopars between manual and power brakes. Try to stop an F with no booster some day. Takes a Russian weight lifter. So a set up like Big Red , all manual, has to have a pedal arm taken from a manual brake car and have to redo the master height too , re: the upper pivot place , to accommodate that new ratio, which means a new engine side mount plate etc. from manual brake cars. New holes in body too. I made the mistake once, just canning the booster, you cannot stop that car; time for plan B. But with stock manual brakes that pedal arm ratio change sent you to less stroke per pedal inch moved to gain the needed increase in PSI leverage ,( like a hydraulic floor jack) = less cc per full pedal stroke movement, but higher pressure, so discs on mopar manual cc design get dicey..as total volume (CC moved per stroke of pedal ) apparently goes down ,on manual drum brakes. And often narrower MC bore on manual which also raises PSI, but again less cc . Manual 60 brakes are great in my opinion, as effective as power, if all this is factory stuff. Same shoes /drums too. No dependence on vacuum. (why I did it) . I think there are several bore sizes in our 60 plus or minus identical looking single pipe MC packages too, another thing to be aware of. You get the wrong one , looks the same, you join a new dance.

Add to this the limited space around rams ,no room for typical in line booster, a real , no two ways about it, need for a physically large dual master, you got a big hassle. ,. All this is by way of information, not taking any positions, but change only one part of brakes at your risk, or at least with understanding of all this. .And if you do so understand , you might lose some safety margin built in , also against leaks,--- that margin was designed for another type of wheel end design. (The Dart surprise) . That risk is obviously more acceptable with a dual master.

This info is really good, Jim; Bosche engineering data about what one might expect ,and then the designers deal with it in the brake SYSTEM design, which is a lot more than just what is on the wheels??.

We have great site, learn a lot as we go……

From: BARJAM300@xxxxxxx [mailto:BARJAM300@xxxxxxx]
Sent: Thursday, September 01, 2016 10:25 AM
To: jkg@xxxxxxxxxxxxxxxxx; awrdoc@xxxxxxxxx
Subject: Re; Caliper retraction measurement procedure

FYI,

Jim B