Pick up trucks have a proportioning valve that varies the braking power
to the rear wheels based on how much weight is being carried. More
weight = more braking power to the rear wheels.
Stephen I. Early
Card Services Technology
Bank of America Corporation
800.441.7048 x74788
stephen.early@fiacardservices.com
-----Original Message-----
From: owner-bricklin@autox.team.net
[mailto:owner-bricklin@autox.team.net] On Behalf Of John T. Blair
Sent: Thursday, November 15, 2007 2:14 PM
To: Bricklin@autox.team.net
Subject: Proportioning valves?
I've got a question for all you mechanics out there.
I was having a discussion with a friend from work. He has a friend
that is having problems with the brakes on his truck. So they bleed
the system, which help some, but not a lot. So my friend asked me
if I had any suggestions.
I asked him some questions about the truck, ie, year, make, model, etc
which he couldn't answer off the tope of his head. So I made a couple
of suggestions. One was to do an internet search for the problem and
see what popped up. The other was, about bleeding it. I asked if it
had ABS. He said yes. I asked if they'd bleed the pump and or master
cyl, not knowing the specifics of the truck. I've read that different
ABS systems require specific procedures for bleeding.
I'm getting to the question. But felt the backround was necessary, and
this does apply to the Bricklins.
A couple of days later, he sends me an article that he found on the
internet about specific problems with the brakes on Dodge trucks.
Dodge Truck Brake Problems
http://groups.google.com/group/alt.autos.dodge.trucks/browse_thread/thre
ad/
b161f87b407dc9d1/f8c566099a9681e5?lnk=st&q=ram+brake+96+bleed+dodge#
f8c566099a9681e5
(Which it turns out was what his friend had.) The long and short of the
article was that the proportioning valve was bad.
This is where I need some help. I realize that the front brakes do most
of
the stopping. In most of the cars, I've worked on, the brake pedal
works
against the power assist unit, which amplifys the pressure exerted by
the
driver. This increase pressure is in turn transmitted to the master
cylinder.
I think I correct on this, and it makes sense.
Now if I only have a single system brake system, like on my Morgan, I
can see
the need for a proportioning valve, to split the force exerted to the
front
vs the rear brakes.
But on the new cars with dual brake systems, I thought the master
cylinder
basically did that.
So why the proportioning valve?
On my Spitfire, it's not called a proportioning valve, it's called a
Pressure Differential Warning Actuator "PDWA" and appears to be very
similar to what's on the Bricklin. When either of the 2 brake
subsystems
has a problem, this can tell the reduced pressure on the one side, and
the internal switch is triggered. This turns on the "Brake" light on
the dash to tell you, either you have the emergency brake on, or there
is a problem with the brakes.
So what is the proportioning valve, how do they work, and why are they
needed on a dual braking systems?
John
John T. Blair WA4OHZ email: jblair1948@cox.net
Va. Beach, Va
Phone: (757) 495-8229
48 TR1800 48 #4 Midget 65 Morgan 4/4 Series V (B1106)
75 Bricklin SV1 (#0887) 77 Spitfire 71 Saab Sonett III
65 Rambler Classic
Morgan: www.team.net/www/morgan
Bricklin: www.bricklin.org
If you can read this - Thank a teacher!
If you are reading it in English - Thank a Vet!!
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