RE: [Chrysler300] 300F Brakes

Hi Terry,

You need to be sure the master cylinder gap at end of push rod is right..there has to be some free play, to avoid power unit acting incorrectly , but it should be minimal..check service manual , I do not know exact number ; I think there is a return stop for pedal “up”, it is rubber, it can wear a bit so pedal comes up a bit more than when new ..this increases stroke available (might be good, in my book) but also, uncorrected for, increases gap to MC piston at end of push rod, so it moves some before piston moves any. Some mopar, this rod is adjustable, some fixed…do not remember F specifically..at work. Might impact trip point of power booster too, have to read the manual, and understand adjusting all that. They interact. On that point, the early manual, 300C or 57 book has I believe a lot more on the brakes..maybe 55 and 56 too. By F they assumed service guys knew about brakes, some parts of text were left out ; same with torquefilght, -----I think later on, I found a 55 or 56 , 57service manual, the powerflight section in earlier book has a much better explanation of hydraulic governor based reverse lockout action (problem I was having), even than the torqueflight one..in same book! ( be sure governor weights pull back all the way, is the takeaway) .

I think Chrysler often very carefully explained new things, but only the first year…later years can be condensed.

Related to pedal play, nylon bushing inside pedal arm at pivot can get worn .

You can “feel” this kind of play with hand or foot…The pedal moves “without doing anything “ then you feel the increase as rod touches piston inside MC , takes up the gap.. Other kind of play is within the brakes, MC piston moves some before brakes touch drums fully. In all honesty, Terry, if “work done on brakes” was not done by a real pro familiar with these brakes you can be truly driven crazy. I was unable personally to get play out the first 300F I owned, way back in 1970, all new parts, ---and I thought I knew my stuff ; I did find a guy who knew about them in the day, he made them perfect (after frustrating 4+ tries by your truly !); this is particularly true if new shoes or drums; first, if not precision ground, rapid wear happens (NORMAL!)-- if shoes are not arc ground to drums perfectly..which no one does anymore, which causes the pedal to drop fast in first 2-3k miles, as shoes seat. First they only touch drum at one end. , but then after some rapid wear they are fitting right. Before that , adjustment of cams may seem to slip , be fussy, or not hold(see later on that, too) ..ok for a short time, then problems; ( this was my problem back then, I did not understand about this rapid wear) ---if you DO understand, you can get through this. But having no self adjusters , you have to adjust frequently at first on typical “just replaced shoes” . And your new brakes “feel poor” , pedal is dropping, after 10 stops!. Second part is human error; I have found a surprising number of people who ought to know better turn the cams the wrong way , “until they feel drag “ without looking at the diagrams ; they will feel drag coming at the adjustment backwards (!) but it will not hold and is all wrong. Have that drawing right in front of you, which way to turn cams to tighten,..and back axle IS different . It is also possible to have the big flat spring between the plates, about 6” long on wrong side of cam(!!) , backing plate put together wrong, had that too. Brakes all screwed up, but OK at first but then soon pull ,sometimes violently , to one side .

These brakes are actually not as bad as buzz rep would have, ---most of the bad stuff comes from someone being in there wrecking them by bumbling around. From a pure design / engineering standpoint, they are much better conceptually than later Bendix, as in that later design only one shoe does most of the work(one leading shoe, although some transfer happens..long story) --- and 11” drums have less leverage than F’s 12”with two leading shoes , but they are fairly precision things to get right..and few are REALLY right once someone gets in there. Lining area not that much different despite wider shoe. I have a 60 Buick 225 convert (F’s only real competitor!) brakes are unreal good by feel..the aluminum finned ones, but that has nothing to do with around town feel,--so could see how people in 1960 thought 300 brakes were poor.

From memory, want to bring up that we believe Mopar did a major upgrade to brake mountings in mid 58, along with upsized ball joints= new control arms (we must know !!--!!wonder why!!….!); I got into this , on crazy conflicting listings for 58 brake parts and ball joints , stuff that did not fit. I looked into this, late 58, 59 up control arms, and especially backing plates are made of much heavier metal, that flat spring is beefier, lots of stuff, wheel cylinders different, reason is thickness of the backing plate sandwich changed, due to thicker metal, wheel cylinder “foot” changed size ; we have used 60 brake parts on earlier cars, by changing backing plates, knowing this. Not relevant to you, but while hitting on “Total Contact” brakes …whole 59 up control arm and brake ought to fit 57, early 58. There WAS a reason.

Last, the washers or flat springs that hold the cams by friction when turned can get loose to the point that the cams will not stay put; this happens on a resto when long rusted in place, and then forced/broken free, and the original sort of friction holding of the flat sort of “Belleville spring” is reduced or broken ; this problem is really a big one for our cars, maybe someone will make a kit of new cam parts, or even some type of locking nut (another way) to set them up and then be sure they stay there. In general not made to be taken apart . (like door handles!) . …a some day soon project.

You give me a chance to share some stuff; might help, hope so.

John

From: Chrysler300@xxxxxxxxxxxxxxx [mailto:Chrysler300@xxxxxxxxxxxxxxx] On Behalf Of Terry Mctaggart terrymct999@xxxxxxxxx [Chrysler300]
Sent: Monday, July 14, 2014 9:39 AM
To: Chrysler300@xxxxxxxxxxxxxxx
Subject: [Chrysler300] 300F Brakes

I recently had some major work done on the brakes (new wheel cylinders, new master cylinder) and the car stops straight and true, but the brake pedal is lower than I like. Is there an adjustment I can make to raise up the effective point on the pedal? Terry McTaggart