In message <950725212102_122939472@aol.com> writes:
> Does the PDWA in the TR6 braking system actually shut off one of the
> halves of the brake system? Or does it just warn the driver that there is
> a pressure difference between them?
>
> Near as I can tell from the work I've done on the brake system, and from
> the manuals that I have, that the PDWA simply warns of a pressure
> difference. From what I could tell when I took my PDWA apart the gizmo
> doesn't appear strong enough to actually shut down any part of the brake
> system.
>
Bruce,
I think there are both kinds depending upon your dual master cylinder. There
are those who sware up & down that there is a mechanical connection between the
two master cylinders and if the front circuit goes the mechanical connection
will push the rear cylinder. The late sixties and early seventies Land Rovers
evidently had this kind of Gurling Master cylinder. They didn't even have a
PDWA. On the other hand I recently converted my 1960 109 Land Rover over to
power Dual brakes using components from the last of the 109 Land Rovers
(mid-80's). The master cylinders did not have a mechanical linkage between the
two, and the PDWA is relyed upon to close a blown circuit. I had a friend from
Australia FAX the relevent pages from his later Land Rover manual. The PDWA on
my 1968 MGBGT closes off the curcuit if it is tripped by low pressure.
Remember, you have two vertical holes and a horizontal line that goes between
with a piston in the horizontal hole. If clearences are right, and the horz.
hole is a little longer than the space between the vertical ones, the piston
could cut off the flow. Its only importasnt to do that on the circuit that
belongs to the mechanically operated master cylinder. Some PDWAs may be set up
to do this since on one side only since some are set up with different sized
threaded openings that match different sized openings on the master cylinder.
Which combination the TR6 has I haven't a clue. My TR3 has a single. I jusat
wanted people to be aware that there are at least two different kinds of dual
master cylinders and at least three kinds of PDWAs out there. If you have the
master cylinder without a mechanical linkage it is important that you have a
PDWA that cuts of at least one circuit. If you have a master cylinder with a
mechanical linkage between the cylinders, it doesn't mater which, or if you have
a PDWA installed.
Take care,
TeriAnn
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