I don't know about the ones you have, but proportioning valves in general
keep 10# pressure on the back brakes to take up some spring travel. Many
brake master cylinders have a compensating valve in them that keeps 2#
pressure in the line to take up some of the seal lip retraction for the
calipers. When you have everything right this is very nice--no pedal
motion before the brake actuates. If it's a bit too much you'll get drag.
Clutch master cylinders have no compensation because you don't want to
keep pressure on the throwout bearing or on the thrust washers for the
crank. If what you are feeling is a little drag then you have just a
little too much compensation. The purpose of compensating pressure is to
keep the shoes or pucks close to the drum or disk. I think you're better
off with no rear drum pressure and just keep your brakes well adjusted.
Front disks usually work very well with two pounds--no drag, just less
pumping.
It's a matter of taste I guess, but I don't really like proportioning
valves--they are too much of a compromise.
-----Original Message-----
From: Joe Curry [mailto:spitlist@cox.net]
Sent: Sunday, August 24, 2003 3:00 PM
To: fot@autox.team.net
Subject: Brake Proportioning system installed oops!
OK, guys, I need some help here. I installed the Tilton brake
proportioning assembly on dual master cylinders to be able to adjust the
proportion front to back, as several suggested.
Today I tried it out. The result is that the brakes lock up and will not
let go until I release one of the bleed valve on the calipers.
I used clutch masters because I had them on hand and they are the same
size as a brake master for an early Spit except for the reservoir.
Question is, despite the same bore size, is there something else that
might be different and keep the pressure on the line after the pedal is
released?
I can probably come up with a pair of brake masters if they are indeed
different, but as far as I can see, they are not.
What else could be causing this? I tried different size actuator arms and
hage induced free travel in the linkage but I can't seem to find the cause
of this problem.
One more thing, there is no free pedal play with this system. The rear
brake master has very little play before they grab and the fronts do go in
a little further but appear to keep the piston in place after the pedal
pressure is released.
I disassembled the master cylinders and inspected the springs and they are
strong. So what gives here? Anyone???
Regards,
Joe (C)
P.S. I did alright today at the autocross. 4th overall despite having to
drive through locked brakes! :)
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