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Home » Public Forums » GMCnet » Problem with brass body proportioning valve (Read about it in Winter 2021 Vintage RVing)
[GMCnet] Re: Problem with brass body proportioning valve [message #365334 is a reply to message #365293] Sat, 10 July 2021 11:08 Go to previous messageGo to previous message
Thomas Pryor is currently offline  Thomas Pryor   United States
Messages: 143
Registered: January 2011
Karma:
Senior Member
Well yet again Dave Lenxi hits a home run with his issue 154 (article) To
further support his findings if you look up the distribution valve in the
parts book it calls out ; "VALVE ASSY-metering balance and distribution
switch (SOA)(repl1236005)" It DOES NOT describe any rear brake pressure
limiting feature. DO NOT use the word PROPORTIONING when describing the
GMC MH distribution or combination valve. It is not supposed to limit
pressure in any way to the rear brake channel. The real problem that
should concern us all is, the available replacements for the GMC METERING
BALANCE AND DISTRIBUTION SWITCH valve assy are generically called PV2 or
PV4. These all have pressure limiting features to the rear wheels.
Without a direct replacement of the Cast iron Metering balance /
distribution valve we can follow the alteration/modification instructions
shown in:
https://www.classicperform.com/Instructions/PDF/Prop_Valve_Mod_Instructions.pdf


Again Dave uncovers a well hidden piece of knowledge, a tool that is
supposed to be employed when bleeding the brakes. You are supposed to
remove the electrical switch from the valve body and insert a tool in its
place. The tool then restricts the shuttle effect that actuates the switch
for the dash brake light. Holding that "shuttle" allows for more effective
rear brake Bleed. See pages 5-14 and 5-15 of the maintenance manual shows
the use of the J-23709 tool. That piece of information has been in our
Archives for 50yrs, who knew? That tool continues to be used on today's
available combination/proportioning valve. SEE:
https://techtalk.mpbrakes.com/proportioning-valve-bleeding-tool

The end result of this discussion is:
1. If you have a Cast iron distribution valve,......... care for it by
Flushing your brake system now and often. Moisture kills the Cast iron
sealing surfaces.

2. If you have a brass distribution(combination) valve fitted on your
coach,.... it is not as original equipment functionality and reduces rear
brake pressures significantly. In other applications the PV-2/PV4 valves
are appropriately modified as shown here:
https://www.classicperform.com/Instructions/PDF/Prop_Valve_Mod_Instructions.pdf
If you want cost effective braking improvement, just do it!

3 For those who have had issues with Brake bleeding get the bleeding tool

I am sure that many will comment that I have used Brass valves for the last
twenty years and have had good brakes and have been able to bleed them. "I
have always had good brakes." MY REPLY MUST NOW BE AS COMPARED TO
WHAT........SHOW ME THE DATA!


--
Regards,

Tom Pryor
4188 Limerick Dr
Lake Wales, Fl 33859
Cell 248 470 9186

1977 23'B named "CASPER", HARDLY ORIGINAL, (455 EFI) (Pwr. Drive)
(tailgate) (rear bunk beds)
(Webasto petrol boiler) (MB Elect fan clutch) (Brake reaction arms) BUT
STILL A WORK IN PROGRESS!

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