RE: [Chrysler300] 300F Brakes

Hi Terry,

First , just a comment to help you ---is there a (big) gap there? No point getting adjustable one if gap is already about right..by looking you can see it move, move pedal with hand, you can feel it touch master piston, might even hear it. Sometimes rubber boot is gone you can see it , the play. The piston stops all the way out by a seat or stop (? Snap ring in MC –not controlled by rod if done right ) , rod pulls back a bit or might just sit like that..so expansion of fluid , all that stuff cannot make piston move farther than the inside MC stop..on some . Do not want to shoot from hip, important thing , but to my knowledge/memory, once piston is stopped , by its own means, inside MC, fluid return ports are open, so gap SIZE cannot impact fluid action inside MC? But gap HAS to be there, so piston does come out all the way—never held in by rod . But gap size is involved with triggering power booster above it and that is what is in service manual ..and very critical; I do remember adjusting gap on non power brake 60 to about .010, just enough to be sure there IS a gap, also fighting low pedal, but long painful story on that , a modified car.

Without getting into that car too much ----but sharing scars from that car,---- you cannot just take away booster and have manual brakes..pedal arm ratio is all wrong , unbelievably hard to step on. (been there) Need pedal arm change and manual MC ,which has a smaller bore and ? longer stroke in some years (I think) , Any chance wrong master, thinking of that? Did you change it? ? (YES!) manual small bore master? Will move more for same CC. might have wrong master cyl! Or sticking piston not coming out all the way?

But, on power brake car, if you DO convert to different ratio or setting manual pedal and manual master, distance from fixed upper pedal swing pivot to center of rod is now longer or shorter (forget which) too, so master ends up in wrong place vertically even if you change it . Rod is then angled, no good. So master mount plate must be different or pedal pivot mount setup behind dash. (never resolved all that) None of this relevant to you, but might help someone , and made me aware of (apparently) different masters, pedal arms, ratios, possibly MC mount heights . Not at all as simple as it looks in there.

It really sounds like what you going through is identical to me 40 years ago, if MC is right ..all perfect, all stock, low pedal. It WAS , in fact, the lack of contour on brake shoes vs drums, despite my hand falling off from “adjusting it”, before a pro “arc ground” them to drums. I still think we might have that here, unless same shoes went back in. I have done brakes since without grinding but might have to wait few thousand miles before it calms down . And as someone very correctly pointed out, if this was all OK before brake work---- it cannot be that rod..in fact messing with it may do a lot more harm than good… if not the problem--- and I doubt it is. Why they took away adjustment!

Part # on master? Bore size ?

From: Chrysler300@xxxxxxxxxxxxxxx [mailto:Chrysler300@xxxxxxxxxxxxxxx] On Behalf Of Terry Mctaggart terrymct999@xxxxxxxxx [Chrysler300]
Sent: Friday, July 18, 2014 10:06 AM
To: Listserver Chrysler Club
Subject: [Chrysler300] 300F Brakes

The saga continues. New master cylinder; new wheel cylinders. Brake adjustments at the wheels are right on. No air in the lines. Car stops straight and true, but the brake pedal is low. According to the shop manual, the adjustment for "pedal free play" is in the conection between the brake pedal assembly and the master cylinder. This connection is a two-part piece, Part 1 being "the end" which connects to the brake pedal assembly, and Part 2, called "the master cylinder push rod", which screws into Part 1. This screw end provides the adjustment. In my car, there is only one part, hence no adjustment is possible. Does anybody know where I might be able to find a two piece end/push rod assembly? Terry McTaggart