On Mon, 27 Feb 2006 03:12:35 -0700, you wrote:
>Date: Sat, 25 Feb 2006 18:27:17 -0500
>From: "Mike Sergesketter" <mserges@psci.net>
>Subject: [oletrucks] Soft Pedal on power disk/drim brakes
>
>Hey Guys,...[...]...I have been bleeding and bleeding the
>system, have brakes, but a very soft pedal...[...]...I was told that I did not
>need a residual valve on the
>lines...could this be causing the soft pedal?
============================
Very possibly. 10 lb residual valves are used in drum brake circuits
to prevent air from pumping past the wheel cylinder cups on the return
stroke as the pedal is released. (Yes, I know that a couple of the
brake vendors' sites say that the valves are to keep the shoes out
against the drums, but they are WRONG. It takes typically about 60-70
lbs of fluid pressure to overcome the tension of the return
springs--10 lbs ain't gonna keep 'em stretched. The brake shoe
adjusters do that job.) Depending on the design of the wheel cylinder
cups (thick rim or thin rim) they can pump a lot of air.
As Wayne says in another post, if you didn't bench-bleed the master,
do that first. That may fix your problem. If not...sounds like your
proportioning valve is an OEM from a donor truck. If it came from a
disc/drum truck, it probably has a residual valve built into it.
Nowadays they call them combination valves, because they combine up to
five functions in one part. But it may not, or if it has one it may
not be working properly. So...get and install an inline 10 lb valve
from CPP in the rear brake line.
Another issue that arises with frame-mounted masters is the
possibility of fluid siphoning from the calipers back into the master
when on a steep grade. Using a 2 lb residual valve in the front brake
line will prevent this without causing the pads to drag on the rotors
and overheat. But with a remote reservoir, the siphon outlet moves up
to the reservoir, and you probably can't get the truck nose-high
enough to have that problem.
Joe.
--
Heather & Joe Way
Sierra Specialty Automotive
Brake cylinders sleeved with brass
Gus Wilson Stories
http://www.brakecylinder.com
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
|