Re: [Chrysler300] Brake booster

[Michael Moore <mmoore8425@xxxxxxx>]

Paul, my 300H had that problem. After trying eveything else, I decided the low pedal was caused by the pushrod between the master cylinder and the booster needed adjusting, something the shop manual says not to do.  

There needs to be a small amount of clearance between the master cylinder piston and the pushrod from the the booster to accommodate expansion of brake fluid.  

On another make car I have, I found that too little clearance will cause the brakes to set up. I never found a reference to how much clearance there should be on my car, but decided .060 was a good place to start. 

It's tricky to measure the depth of the piston in the master cylinder, but by measuring that and the length of the adjustable rod coming out of the booster, and a little arithmetic, I found  I had something like 1/2 inch clearance.  
 
If you consider the pivot point of the brake pedal as a reference, then measure from the pivot to the booster rod, you'll find a small number , say 2 inches.  Then measure from the pivot to the brake pedal, you may find 11 inches. This is a multiplier of 5-1/2  to 1. So if you have 1/2 inch clearance and can reduce it to .060 (1/16), you'll raise the brake pedal by ca 2-1/2 inches. (I have made up the lever numbers as I forgot the real numbers, but you get the idea.)
 It made a huge difference in my brakes.
Best Regards,
Mike Moore


On May 6, 2012, at 9:10 PM, Paul Martin wrote:

I am just finishing up the AAJ disc brake conversion on my 300F. I have evacuated the air from the lines and have a good solid pedel with the car not running, however when I start it up and apply the brakes the pedel goes low to the floor,not all the way and the car still stops but not well. I double checked to make sure all the air was out of the lines.

Ant tips? Is there something I need to do to the booster.

Any help would be appreciated.

Paul Martin

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