<VV> Dual or single master cylinder

[JVHRoberts at aol.com]

Not to be argumentative, but I did the mashing thing, and it still went to  
the floor. Not the case with the Subaru and Nissan brakes. It went down on 
those  cars, but not to the floor, and I had plenty of pedal to lock up the other  
circuit, presumably... 
 
In a message dated 12/5/2005 5:48:10 P.M. Eastern Standard Time,  
NicolCS at aol.com writes:

<snip>JVHRoberts at aol.com wrote:
... leave only one bleeder  open on a Fiero, and the pedal goes damn near to 
the floor!  ...
<unsnip>

Someone correct me if I'm wrong (Patrick /  AngryP?) but...  If you have one 
bleeder open, the pedal will sink to  the floor - this is how we bleed 
brakes.  
If you mash the pedal and  one circuit is out, the combination valve will 
detect the difference in  F/R pressure and the shuttle valve will move to 
block the 
offending  circuit and turn on the "brake" light. Takes the reverse to 
recenter 
the  shuttle (some have a centering button on the end).  (Some later  
combination valves automatically isolate the circuits and you have to use  a 
special 
tool on the end-button to allow bleeding.)  All dual master  cylinders have 
two 
pumps and two outlets.  The difference is in the  combination valves.  For 
our 
cars, if one circuit is out, mash the  pedal to seal-off the bad circuit and 
stop 
using 1/2 the brake  system.  
Craig Nicol