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

[Ken Pepke]

Back in the day the dual master cylinder was claimed to maintain braking effort at one end of the vehicle during a failure of a major component on the other end.  TV demonstrations showed a vehicle still locking up the front wheels when the rear had failed.

I have always assumed that all Corvair dual master systems had the slider valve [a block with lines attached adjacent to the master] because the 1966 system I installed on my 63 was so equipped.  And, it worked as expected.  Failure of a rear wheel cylinder caused the valve to slide which resulted in a very high, very hard pedal.  The car stopped almost as well as normal and the only clue was the increased pressure required on the pedal.  Once repairs were made the real trick became getting the slider valve back in the center.

Now the question becomes 'was this stock or did a PO add it to my parts car?'  
Ken P

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Begin forwarded message:

> From: Sethracer at aol.com
> Date: December 28, 2010 1:19:39 AM EST
> To: fastvair at yahoogroups.com, virtualvairs at corvair.org
> Subject: <VV> brake failure? - Probably not the master cylinder
> 
> 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  
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