OK guys and gals.... it's simpler than you're all
making it!
The dual ckt master works like this.
As you first apply pressure, the front ckt
sees the peddle pressure you applied.
Once the pressure is applied to the front ckt and the
piston i nthe master cyl has passed, and closed off
the intake hole from the reservoir...
and as you continue to apply pressure...the pressure
in the master cyl itself starts pressurizing the rear ckt.
So the fronts will have pressure before the rears,
and unless the front ckt pops a cork, the rears would
never have more pressure than the fronts.
There is no 'proportioning valve' in the ckt. The
little do-hikky (what ever it is you all want to call it)
activates the failure warning light when one ckt sees
massive pressure when the other doesn't. If the
fronts were working, and the rear leaking badly,
no pressure is built up in the rear of the master cyl.
So the differential valve sees high press. on one side and
not the other, thus shuffling it off-center. And visa-versa
rears to front. It is NOT designed to seal off the
damaged ckt. But in many cases it seems to.
Bleeding the brakes properly, requires you to re-center
the shuttle IF it was knocked off-center. This Too, can
happen if too 'robustly' trying to bleed your brakes.
Yes...your brakes will work just fine without the differential
valve in the ckt. But you'd never know that one of the two ckts
is not working, until the second one fails, leaving you with
NO brakes at all. Just like it sounds like what happened
to your friend leaving the pits.
Paul Tegler
ptegler@cablespeed.com
www.teglerizer.com
----- Original Message -----
From "Bob Van Kirk" <racerbob70 at yahoo.com>
To: "Gerard" <pixelsmith@gerardsgarage.com>; <spridgets@autox.team.net>
Sent: Thursday, May 15, 2003 8:46 PM
Subject: Re: dual braking system
> Gerard,
> Thanks for your input. This car didn't have the
> proportioning valve in the system. Just a line
> connected to the master for the fronts and a line
> running to the rears. No one has said that "yes it
> must be on the car" but after studing the master
> cylinder cross section and having rebuilt several I am
> begining to think that it has to be in the system. I
> believe that the valve of the front system needs the
> pressure from the closed off section of the proportion
> valve to actuate the rear system in the master. There
> isn't a solid push rod all the way thru the master but
> 2 rods connected by pins and a spring, sort of a
> proportioning valve in itself? The pressure from the
> front part, after starting to actuate the discs, then
> pushes the rear rod and valve forcing the rears to
> start doing their job. If you have a pressure failure
> in the front system, as my friend did, the rears won't
> work if the PDWA isn't there to shut off the front
> line. In the other case were the rears fail, there
> isn't enough difference in normal every day braking
> for the average driver to notice thus the inclusion of
> the warning light in the PDWA system.
> Imput?????????
>
> Bob
>
> --- Gerard <pixelsmith@gerardsgarage.com> wrote:
> > Cap'n (and others following this discussion),
> >
> > Nope, not diagonal. Circuits are front and rear and
> > probably set up the
> > same way front and rear without the valve.
> >
> > Also, I don't think the system is designed to
> > conpensate for a leak, but
> > rather a loss of pressure.
> >
> > The proprtioning valve has 5 connections, two from
> > the MC, one to each
> > front wheel and on out to the rear tee. One MC line
> > feeds the front and the
> > other the rear and front and rear are supplied from
> > corresponding feeds. If
> > pressure drops from one supply, it will force the
> > shuttle valve to pop to
> > the weak side allowing fluid to supply both
> > branches. Unless someone can
> > explin otherwise, I think you are still in trouble
> > if you spring a leak
> > somewhere.
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