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

["sjak brak" <imperial1973@xxxxxxxxx>]

The adjustment procedure is generally identical for aftermarket master cilinders, but indeed, specifications may - and will - vary. Also, stock replacement parts can vary due to loose production tolerances.

 

Another thing to take special care of is properly and thoroughly bench-bleeding the master cilinder. In some cases, I have seen it take more than 3 hours before it was fully bled. A good practice is to wait a bit after some bench bleeding, possibly give some gentle hits on the cilinder with a rubber hammer, and continue the bleeding procedure.

 

On 11/27/07, PAUL WENTINK <randalpark@xxxxxxx> wrote:

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.