Re: [Chrysler300] Master Cylinder / Brake Pedal Problem

Henry,

I know nothing about 300D brakes, but I know a bit about my 300H brakes.

My master cylinder recess in the piston mates with a rod in the booster. When the booster pushes, the rod pushes on the master cylinder piston.

There are all sorts of warnings in my shop manual about not adjusting that rod.

There has to be clearance between the end of the rod and the seat, although I never found a specification for that. My booster had been replaced and also rebuilt, and my master cylinder had been replaced, so I decided that needed to be adjusted. I once had a tool made by Chip Chapman which set the rod to the correct dimension. It was piece of sheet metal with a carefully machined slot.

If you were measure the distance from the brake pedal pivot point to the master cylinder piston pushrod, and compare that to where the pedal is from the pivot point, you will find a large mechanical advantage. If we assume it’s 4 to 1, then 1/8" reduction in clearance between the rod and the piston will raise the pedal by 1/2 inch.

If you reduce the space too much, expansion of the fluid will eventually lock up the brakes. I used a dial indicator and some simple tools and measured the depth of the piston recess and the protrusion of the rod, subtracted one from the other and that’s how how much clearance I had to work with. There is an acorn-nut-like bolt on the end of the actuating rod. I held the rod with a small pipe wrench on some rags and gradually lengthened the rod. I do not recall what I ended up with for clearance, but I raised the pedal substantially and my brakes do not drag, so I’m happy.

Mike Moore 300H

On Mar 21, 2014, at 6:20 AM, Henry Schleimer <henry.schleimer@xxxxxxxxxxxxxxx> wrote:

Adjust the brake shoes to take out all slack before bleeding. If there are no leaks at any cylinders and there is still travel, there is still air in the system. The fluid doesn’t compress to any degree. If no further luck, take it to a professional brake shop. Sometimes air just shuffles back and forth and those with more experience know how to get the b*st*ard out!

From: Chrysler300@xxxxxxxxxxxxxxx [mailto:Chrysler300@xxxxxxxxxxxxxxx] On Behalf Of josh@xxxxxxxxxx
Sent: Friday, 21 March 2014 2:49 PM
To: Chrysler300@xxxxxxxxxxxxxxx
Subject: [Chrysler300] Master Cylinder / Brake Pedal Problem

Hello guys.

I rebuilt the brake system on my 1958 300D (Manual Brakes). I ended up with a new brake cylinder from Kanter. After installation I noticed the pedal almost went to the ground. I don't think it's air. I bench bled the M/C and pressure bled the lines and wheel cylinders several times.

The brakes stop normal and hold, but the pedal has to travel near the bottom.

I adjusted the shoes several times, they seem to be adjusted as per the manual.

I was also able to extend the pedal shaft which helped some... but it's maxed out to where I still have sufficient thread.

ANY IDEAS, I must be doing something wrong???? THANKS!!!!

Josh Ackerman
Rancho Cucamonga, CA

[Non-text portions of this message have been removed]

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