<VV> Dual brakes fails

[Harry Jensen Executive Secretary]

Hi--

I saw the discussion recently on VV regarding dual master cylinders. I 
forwarded it to lclc. Here is his reply.

--H





-------- Original Message --------
Subject: RE: Dual brakes fail >>>>>>>>>
Date: Fri, 14 Jan 2011 10:01:30 -0600
From: Larry Claypool <vairshop at sbcglobal.net>
To: 'Harry Jensen Executive Secretary' <corsa at corvair.org>

Hi all
  The switch on the factory 67-69 brake master cylinder distribution 
black is just a shuttle switch that turns the dash brake light on.

You must understand how the dual master works. 2 separate chambers, 
operated in series by 1 pushrod. There is a spring in each chamber to 
return each piston to the rest position.
  With everything working correctly, both chambers compress until 
pressure is equal in both sides. (the rear  chamber hydraulically pushes 
the front one). Fluid output applies the brakes with equal pressure from 
both outlet ports.

If one side has a failure, no pressure can build up in the portion of 
the master on that side. The spring inside that chamber will compress 
until it bottoms out. At this point the brake pedal has moved halfway 
down, but no brake pressure has been made.
As you continue to press the pedal down, the 'dead' side of the master 
is now fully compressed, allowing the remaining side to begin to build 
pressure, applying the brakes on the remaining side. The apply point 
will be very low, but it will be there.
  Here's the important part- the brake shoes and master cylinder pushrod 
must be adjusted correctly so you have a 'high' pedal to start with. 
Remember when you 'loose' one side, pedal travel increases 50% before 
any pressure is made.  If your brake shoes  are out of adjustment and 
your pedal normally goes halfway down with both sides working, it will 
absolutely run out of travel on just 1 side of the circuit before you'll 
get any pressure.
Yes, dual master cylinders work as designed, but can't do their job when 
the rest of the system is not up to par.
I noted the need for proper shoe adjustment in larry rollow's article 
"dual master cylinder conversion" that ran in the 4/88 communique and 
also in the corvair tech guides vol. 2&3.
I also note the need for proper shoe adjustment in the instructions for 
dual master cylinder conversions I sell. I don't believe other vendors 
address it.
Hope that explains it.
  Regards
Larry claypool