Hi Dave. Just a few tips.
Normally, if you have all the air out of the lines, your symptoms would indicate the master cylinder piston seals are letting fluid get past. Can be internal with no external leaks. Fluid level won’t drop when the pedal drops to the floor.
Possibly air stuck in master cylinder as well. Need to disconnect lines at the master and bleed that first if you let the fluid level drop too low.
I have had trouble getting air out of the rear hose at the axle as a bubble can sit in the high spot unless you are aggressive in your bleeding. Try getting your helper to give quick, forceful, full-stroke pushes when bleeding the rears. I have found a bubble that way. I assume you are bleeding with the shoes adjusted for no clearance so bubbles can’t shuttle back and forth…
Since you may have done all this, I thought I would double check one of my factory manuals for clues. In my ’71 Valiant manual under “Pedal goes to the floor” it also says “Shoe hanging up on rough platform” as a possibility. Something I hadn’t considered, but could be true if the backing plate has ridges in it.
If you can’t find the problem, please go to a reputable brake repairer. This may be a symptom of a serious failure to come.
Henry
From: chrysler-300-club-international@xxxxxxxxxxxxxxxx <chrysler-300-club-international@xxxxxxxxxxxxxxxx> On Behalf Of Robert Hayen
Sent: Monday, 15 September 2025 7:55 AM
To: Nick Taylor <nicksgaragesd@xxxxxxxxx>
Cc: David Dumais <ddume300@xxxxxxxxx>; Chrysler 300 Club International <chrysler-300-club-international@xxxxxxxxxxxxxxxx>
Subject: Re: {Chrysler 300} 1964 Power Braking
Are the shoes adjusted up against the drums properly ?
Sounds like a bad master cylinder. Or the wrong one and pedal travel is not right. Which booster is on the car?
Hey Guys,
I have bled the all new brakes on the 300, many times over.
1: push pedal slowly, hold it open bleeder thru clear hose into jar.
Stiff pedal, but can be pushed to the floor after bleeding.
2: used the pistol grip vacuum hoses and cup, minute pinpoint bubbles observed.
3: wide open bleeder on a slow pedal, holding, squirt and tighten bleeder. Let pedal rise.
After all that, the pedal is firm and can be slowly pushed to the floor.
Start motor and pedal easily pushed to floor.
All the Booster Exchange guys say it's not the booster, but air still in system.
Does the Master Cylinder push rod affect this pedal down to the floor?
Still need to bleed out air?
No visible leaks on cylinders or connections.
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