[DeTomaso] Pantera L 4 Sale

Asa Jay Laughton asajay at asajay.com
Fri Apr 19 10:07:49 EDT 2013


There are two seals working in this system.
One is the square-cut o-ring around the piston in the caliper.  This is 
(typically) engineered to flex a little bit so that after brakes are 
released, the tension on the square-cut seal pulls the piston back to a 
resting position; usually only a few thousands of an inch.  Applying the 
brakes uses enough pressure to overcome this slight tension and allow 
the piston to continue moving outward to take up the necessary slack due 
to wear of the pads and the disc.

However, the pedal return is (typically) not enough to overcome the 
square-cut seal tension to pull the piston back into the caliper, but it 
can.

The master cylinder is (typically) built with a much lighter duty 
one-way lip seal.  When the brakes are applied, the lip seals against 
the bore of the master and applies pressure to the fluid once it passes 
the feed orifice.  When the brakes are released, the lip seal tension is 
(typically) less than the square-cut o-ring tension in the caliper, so 
fluid is drawn in from the reservoir past the lip seal; meanwhile the 
piston in the caliper only moves back against the tension of the 
square-cut seal enough to create minimal clearance between the brake pad 
and disc.

That's the way it's "supposed" to work.

Therefore, if the brake pads are releasing "too far," there may be 
something wrong in the system or the design isn't the best.  I'm sure 
it's true that for whatever reason, some systems tend to pull the piston 
back into the caliper too far.  I couldn't say why.  It would appear the 
residual pressure valve such as what Mike Drew and a few others are 
familiar with, helps reduce whatever the problem is in the system to 
prevent too much play.

I think (my personal opinion) in Mike's case, the RPV is what 
contributed to massive and premature wear of the brakes.  However, I 
also think his thoughts about adding cooling will probably give him the 
most bang for the buck to overcome the limitation he discovered on the 
race track recently without compromising the street driving safety he's 
used to.  (not that Mike drives much differently on the street)   :)

An interesting experiment for Mike to try after he's married, is to 
remove the RPVs for a couple weeks to see if there is any difference; to 
see if he ends up with way too much pedal travel or not.  I would not of 
course recommend going to the race track during that time.

Asa Jay

Asa Jay Laughton, MSgt, USAFR, Retired
&  Shelley Marie
Spokane, WA
******************************
http://www.racingagainstautism.com
http://www.teampanteraracing.com
http://facebook.com/racingagainstautism


On 4/18/2013 11:07 PM, The DeTomaso Registry Guy wrote:
>
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> Anyone know this car?
>
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> http://monterey.craigslist.org/cto/3662449243.html
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> Chuck
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