Re: [Chrysler300] A serious 55 Kelsey Hayes issue - brake failure

[Michael Moore <mmoore8425@xxxxxxx>]

Thanks Rich,
They are pretty clear that there should be 1/8 to 1/4 inch pedal looseness-but that doesn't have power brakes. That relates to the .150 clearance I had  between the booster and the master cylinder. What they are saying, if I understand correctly, is that there should be .125 to ,250 clearance between the adjustable pushrod and the master cylinder, I don't think the master cylinder cares if its being pushed by a plain old foot or a power brake booster.
The 150 clearance I had was probably correct then, although I reduced it way down to get a higher brake pedal.
Mike Moore
300H 
On Aug 13, 2012, at 5:44 PM, Rich Barber wrote:

On a ?55, the manual says ?If adjustment is made while unit is installed on car?slide a scale next to boot (inside of pedal bracket up to and against dash panel) and measure back to centerline of clevisd pin.  This distance should be 8 57/64 inches.  If adjustment is made before unit is installed on car, measure from reinforcing plate mounted on unit to centerline of clevis pin hole.  This dimension should be 8 61/64 inches, as indicated in Figure 89.  See Manual pages 95-97 at: http://www.jholst.net/55-service-manual/brakes.pdf  
 
Rich Barber
 
From: Michael Moore [mailto:mmoore8425@xxxxxxx] 
Sent: Monday, August 13, 2012 1:26 PM
To: Rich Barber
Cc: 'Narve Nordanger'; Chrysler300@xxxxxxxxxxxxxxx
Subject: Re: [Chrysler300] A serious 55 Kelsey Hayes issue - brake failure
 
Rich,
That is the clearance which my 62 shop manual makes a point about being dealer adjustable only. I have had master cylinders replaced over the years, and my pedal was very low although the brakes worked. 
 
I decreased that clearance from ca .150 down to .060 which got my pedal up substantially (because of the multiplier effect between the pedal to pedal pivot compared to the distance between the pedal pivot and master cylinder linkage) , but I have never found reference as to how much clearance the factory specified. 
 
My 63 Jaguar has a similar setup, but it is a lot easier to adjust so I just kept releasing mine until it didn't seize up any longer.
Does anyone know how much clearance was factory specified?
Mike Moore
300H 
 
On Aug 12, 2012, at 1:20 PM, Rich Barber wrote:
 
 
Narve:

I know you are a thorough guy, but the clearance on the actuating rod from
the brake pedal to the back of the booster is critical. In theory,
retraction of the rod when the pedal is released should allow atmospheric
pressure to flow back into the vacuum side of the booster. If the pedal is
returned by spring pressure, it should retract the actuator rod.

There is a small check valve in the outlet of the master cylinder that is
designed to hold a small amount of residual pressure on the system in order
to exclude moist air. That small check valve may have been damaged or
improperly installed.

Other things to check include the check valve on the vacuum inlet line.

Progress was made over the years. The brake pedal in the '55 is now wide
enough to get both feet on it.

Rich Barber

Brentwood, CA

1955 C-300

From: Chrysler300@xxxxxxxxxxxxxxx [mailto:Chrysler300@xxxxxxxxxxxxxxx] On
Behalf Of Narve Nordanger
Sent: Sunday, August 12, 2012 12:33 PM
To: Chrysler300@xxxxxxxxxxxxxxx
Subject: [Chrysler300] A serious 55 Kelsey Hayes issue - brake failure

Group,

my C-300 has twice this summer had failure on its freshly overhauled brake
system. On both occasions the Kelsey Hayes master power brake appear to lock
up and not letting out the vacuum after I have released the brake pedal.
Brakes stayed locked until I split the master cylinder from the booster.
Anyone seen this before, any remedy?

Additional information: The lightest of touches on the brake pedal sucks it
in and make immediate contact on the shoes, making progressive braking a
difficulty. This was evident both with the old (original) and overhauled
(x-55 De Soto) K-H MC. Having just gone through the brakes on 29 Chrysler
one really wonders if there was any progress at all in the intervening 26
years..

Narve N

C-300 in Norway

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