Sounds like a reasonable inexpensive alternative, Rex.
Good thinking!
Jim
----- Original Message -----
From: "Rex Townsend" <rrt@connectexpress.com>
To: "Sally or Dick Taylor" <tr6taylor@webtv.net>; <jay_welch@juno.com>
Cc: <tom.lofgren@stanfordalumni.org>; <6pack@autox.team.net>
Sent: Tuesday, November 20, 2001 12:11 AM
Subject: Re: PDWA
> Jay, Dick, et al,
> I believe that there has been some misunderstanding of how my
"modified"
> PDWA actually works. First of all, I would NEVER suggest that we
eliminate
> the separation between front and rear brake systems. The setscrews in
my
> PDWA very effectively seal each system from the other as well as
sealing
> each side from the "dry" middle of the PDWA where the switch screws
in,
> thereby maintaining the very important redundancy of the split braking
> system. I can drain the brake fluid from either the front or rear
systems
> and still have braking on the other end of the car. Jay, I do not
> believe that the PDWA functions as a proportioning valve. (Note: the
UK and
> other non-U.S. TR6s did not have PDWAs.) The PDWA simply slides to
one side
> or the other to trip the warning light switch when the pressure is
> significantly different from one side to the other (i.e. when you have
lost
> fluid on one side). A proportioning valve, on the other hand, has to
have
> some sort of active unit that changes the pressure differential
between the
> back and front systems in relationship to increasing pressure by the
> operator. Often, this is a pressure reducing valve to prevent the
pressure
> in the rear system from climbing at the same rate as the pressure in
the
> front system. This reduces the tendency to lock up the rear brakes in
hard
> stops. However, the TR6's PDWA doesn't change pressure on the rear
system
> as the pressure increases - its piston only moves when one side has
lost
> pressure completely. You can verify this by moving the PDWA piston
from one
> side to the other (you can do this by unscrewing the warning light
switch
> and using a bent piece of wire to move the piston) and then
demonstrate that
> the brakes feel exactly the same with the PDWA piston in any position.
> It is my contention that the only purpose of the PDWA is to
actuate the
> warning light when pressure is too low to actuate the brakes on one
end of
> the car or the other. The only safety concession I have made in
modifying
> my own PDWA is to eliminate the warning light from illuminating when
> pressure is lost on one system or the other. Remember, the light
won't
> illuminate until you push on the brakes and the pressure differential
from
> the back to front is great enough to move the PDWA piston and trip the
> switch. By then, your foot will already have told you that you have a
brake
> problem!
>
> Rex Townsend
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