Hi Michael,
There is a small hole thatis located directly in front of the
pressure seal called a Compensating Portthat allows fluid to flow into the
master cylinder from the Fluid Reservoir. After much use the lip of the seal
will develop a small groove where it rubs over the port as you apply the
brakes. In time that groove will become deep enough that under pressure the
seal doesn't expand enough in the area of the groove to seal off the bore and
will freely travel forward. Until the groove gets big enough to be a complete
failure you will experience the described problem on
light applications of
the brake pedal. If you apply the brake pedal firmly the seal will expand
positively against the the bore but fluid will slowly bypass the seal as the
seal relaxes. The symptoms you describe sounds like that may be the problem.
You can sometimes evaluate this condition if you get someone to remove the
Reservoir Cap and watch for a slight blip of fluid as you slowly apply the
brake pedal.
Hope this helps,
Ron Mitchell
BN6
BN7
________________________________
From: Michael Oritt
<michael.oritt at gmail.com>
To: Austin Healey <healeys at autox.team.net>
Sent:
Monday, April 30, 2012 7:17 AM
Subject: [Healeys] Brake problem
Yesterday
while returning from a ride in the 100 I applied the brakes and
the pedal went
to the floor--fortunately the emergency brake slowed me down
enough that I
could negotiate the upcoming turn and come to a stop.
After a few deep
breaths I stepped on the brake pedal--this time it was
normal and the brakes
functioned seemingly fine. I checked the hydraulic
fluid reservoir and it was
full. I was less than a mile from the garage so
returned slowly though the
brakes continued to work fine and got me back.
In the garage I applied the
brakes a few more times, all normal except for
one time when I held my foot on
the pedal it and it went slowly to the
floor like I was pushing fluid out
somewhere through a very small leak but
there were no leaks. Next push the
brake pedal was high and firm. Retested
several times at 15 to 30 minute
intervals--no problems, but obviously
something is wrong here!
I haven't
pulled the master cylinder off and apart yet but am thinking that
the return
valve is somehow hanging up. FWIW I have a BT7 discs in front
and drums in
back and a single circuit setup with a valve in the rear brake
line which
serves as a poor man's proportional setup.
Thoughts?
Best--Michael Oritt
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