<VV> Dual Master Cylinder

[John Green]

> I have been confused by this subject since I installed a dual master kit
> (from a major vendor) a few years ago. When bleeding the brakes or flushing
> the brake fluid, the pedal goes to the floor. This is also true when doing
> brake work on our 'modern' 1994 Volvo.
>

John Green
1965 Monza
Corsa member

>
>
>
> Yes this is an important subject (nice way to end the year for this list).
>
> So, how can a person tell if the master cylinder on his/her car (I have
> a 68 convertible) has a fully functional shuttle valve, or just a light
> switch?
>
> Regards from misty Arlington, Texas
>
> jack kean
> 68 Monza Convertible, 140x4
>
> On 12/28/2010 12:19 AM, Sethracer at aol.com wrote:
> > 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.
>
>
> ------------------------------
>
> Message: 2
> Date: Tue, 28 Dec 2010 11:04:28 -0500
> From: Ken Pepke <kenpepke at juno.com>
> Subject: <VV>  brake failure? - Probably not the master cylinder
> To: virtualvairs at corvair.org
> Message-ID: <7F4719A7-D71B-4694-BBE5-6D7B87F93408 at juno.com>
> Content-Type: text/plain; charset=us-ascii
>
>
> 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
>
> **********************
>
> 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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> End of VirtualVairs Digest, Vol 71, Issue 78
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