DeTomaso Mailing List: April 99, Message #266

To throw some more fuel on the fire;

I took a look at the shuttle in my disassembled pressure differential switch
last night, and it definitely does not cut the fluid flow to the 'bad'
circuit of the system.  If one side fails, the shuttle moves across due to
the pressure difference, the differential switch is activated by a small
notch in the shuttle, and the shuttle touches the end of the housing.  The
shuttle is stepped/tapered on both ends, and the end diameters are far
smaller than the bore in which they sit.  Fluid can therefore still flow
past with ease.  If it couldn't, then it would never return to the central
position without disassembling it resetting the shuttle manually.

Incidentally, when my system sprung a leak, the foot pedal did indeed slowly
drop down to the floor with constant foot pressure.  And yes, it was
interesting.  When the pedal was returned to the top position, the reservoir
replenished the lost fluid in the master cylinder.  By the time I got the
car the 5 (very careful) miles to a safe place, the reservoir for the front
system was almost empty, and the lost fluid was found all over the trunk
carpet.

I'll bring the differential pressure switch with me to the tech session this
weekend (if I get my ring gear bolts in time!)

Max


		-----Original Message-----
		From:	Asa Jay Laughton [mailto:asajay@concentric.net]
		Sent:	Wednesday, April 07, 1999 10:41 AM
		To:	Multiple recipients of list
		Subject:	Re: Differential pressure switch -

		At 18:44 04/07/99 +0200, Gunnar Persson wrote:
		>howdy
		>
		>I would have to agree, it is supposed to stop fluid when
faliure is
		>sensed... if it did not the brakepedal would "slowly"
drop..........
		>and it would be kinda intresting if you where sitting and
waiting  for
		>a red light......  ;)

		No this is not necessarily true.  I'm trying to do the
research at home to
		back myself up, but I'm not having any success.  The design
of a master
		cylinder does not really allow for a 'constant' drain of
fluid if your foot
		is on the brake.  The plunger seals inside the bore are
pushed past the
		fluid feed hole from the reservoir effectively cutting off
further fluid
		feed, thus compressing the fluid in the lines to the wheels.
Upon a
		failure, you simply push out what you have, but not drain
the reservior.

		Asa Jay