<VV> brake failure? - Probably not the master cylinder

Tue Dec 28 01:19:39 EST 2010

I spent a half hour looking around on several credible web sites, verifying 
 what I was pretty sure of. "Some" valves act as a warning light switch 
only, not  acting as a true shuttle valve. The true "shuttle valve" should 
slide in  the direction of the low pressure (Blown hose, rusted line, etc.) and 
seal the  blown part of the system from the master cylinder. This would 
allow the floating  piston in the dual master to be solid on one side, 
maintaining and feeding  pressure down the other side, based on foot pressure. 
Without the sealing off of  the bad circuit, pressure from your foot will bleed 
out of the bad circuit  and you will get "almost" no pressure in the circuit 
you still have. Sound  familiar?  If I was building a new in-line dual master 
cylinder system  today, I would add residual pressure valves on the outlets 
of any master  cylinder, since no new replacements have them, feed the 
outputs into a factory  shuttle valve, wire the switch to a warning light, then 
feed the fronts and  rears. According to good sources, neither the Wilwood 
or Master Power   Brakes valve perform the shut-off function, they just set 
the switch. Both  companies have valves that can perform additional 
functions, such as  pressure limiting the rears for lock-up prevention, especially 
important in  a disc-drum combo.

Ready to listen to any opinions - This is an important subject.  Seth  
Emerson  

In a message dated 12/27/2010 9:35:42 P.M. Pacific Standard Time,  
64vair at absolutetops.com writes:

Dual masters will give you something, for that first hit or maybe two,  
then as you see just about nothing.  I think you would find that if you  really 
buried the pedal, you would have had some limited, VERY limited  brakes.  I 
had a hose rupture on my Corvair.  IT was a steel braided  teflon line 
going to the front caliper. (it got pinched, and that is a death  sentence for 
those!).  The first hit had some brakes, after that I was  driving home REAL 
slowly.  From about a 5 mph roll I could stop the car  but it took a couple 
car lengths!  BTW, your brake test is what caused  the failure.  The hoses 
are not made to take that kind of pressure.   I can put 1000 PSI in the brake 
lines with one foot without much  difficulty.  You probably got it over 
2000 PSI just a tad high don't you  think!  When I "panic stop" I hit around 
800 to 900 psi.
Tom

On Mon, Dec 27, 2010 at 9:49 PM, Michael Kovacs <_kovacsmj at sbcglobal.net_ 
(mailto:kovacsmj at sbcglobal.net) >  wrote:

1969 with recent new master cylinder in past few years using Dot 5  
silicon. I 
blew out the right rear hose and have NO brakes. I thought  the dual master 
cylinder was supposed to give me something...NO way. NO  brakes. Brake 
pedal 
prior to the blow out was high and hard.

Who  has had a similar problem? What is cause? Will replace blown hose, but 
why  
NO brakes??

PS : It blew doing the harder..harder..brake test  with both feet on the 
pedal 
simulating a panic stop.

MIKE  KOVACS

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