Re: IML: How Can Changing the Master Cylinder Cause Poor Brake Performace???

[PAUL WENTINK <randalpark@xxxxxxx>]

In this discussion, the poor brake performance would be noticed due to 
the overheated brakes, which can have several causes.

Changing the master cylinder can cause this if the pedal push rod isn't 
adjusted properly. I believe that the adjustment is usually going to be 
at the end of the rod where it comes into contact with the master 
cylinder. Check the FSM for your specific car. It shouldn't require 
adjustment if the replacement master cylinder was the same as the 
original, but the adjustment should be checked anyway. This is more 
frequently a problem when adapting a new style master cylinder dual 
reservoir unit. The overheating would result from the push rod applying 
constant pressure to the master cylinder, causing brake drag. The 
hotter they get, the more they drag due to heat expansion. Using 
non-original parts typically nullifies the FSM adjustment procedures 
and specifications, so basically it becomes a case of trial and error, 
or flying by the seat of your pants.

I recently ran into this with a senior FOMOCO I purchased in this 
condition that had been converted to the new style M/C. Several 
seemingly unrelated problems were all due to the same single item, 
pedal push rod adjustment. These included erratic (pressure switch 
activated) brake lights that would not turn off after the car was 
parked, excessive gas consumption, lack of power, overheating engine, 
bouncing/wobbling/vibrating suspension, and poor brake performance. The 
previous owner had attempted to address each of these individually as 
suspension/tire issues, electrical, carburation, ignition, and cooling 
system problems. As a fellow human being, I can understand the 
temptation to assume that all of these systems failed at the same time 
(Murphy's Law Syndrome), but logic indicates to me that would not be 
likely.

The pedal push rod was adjusted to factory specifications, but not to 
suit the new style part. Correcting that corrected all of the other 
issues, once I had undone the work he had done to compensate for it.

Paul W.


-----Original Message-----
From: dansgarage@xxxxxxxxxxxxxx <dansgarage@xxxxxxxxxxxx>
To: mailing-list@xxxxxxxxxxxxxxxx
Sent: Mon, 26 Nov 2007 9:25 pm
Subject: Re: IML: 1961 imperial front end parts



Hi Paul...after reading your reply to the IMl member regarding problems 
with
wheel 'wobble' or 'bounce' i would like to ask you for more info 
regarding
changing of the master cylinder. I am certainly NOT a qualified 
mechanic of any
kind, I just like messing around with my Imperials (and cars in 
general) so
have learned a little over the years.....just enough to get myself in 
trouble,
as they say!....
...I was wondering WHY you would expect very poor brake performance 
after
changing out the master cylinder? I will very probably be doing this in 
the near
future on my '66 LeBaron so am very interested in what to expect and 
how I might
get around this problem....if, in fact, it really is a problem or just 
something
that needs some kind of adjustment done.
Thanks a bunch!!
Dan Melnik

---- PAUL WENTINK <randalpark@xxxxxxx> wrote:

=============
Wheel wobble or bounce can also be caused by overheated brakes due to
incorrect shoe adjustment, stuck wheel cylinders, or incorrect pedal
push rod adjustment, if you have recently changed the master cylinder.
You would also notice very poor brake performance, especially after a
few miles.

Paul W.

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