| Re: [GMCnet] Correct (and hopefully NON-leaking) brass combination valve? [message #358728 is a reply to message #358697] |
Thu, 17 September 2020 09:50   |
TR 1
Messages: 348
Registered: August 2015
Location: DFW
Karma:
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Senior Member |
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Ken Henderson wrote on Wed, 16 September 2020 17:51My belief in 2007 was that the combination valve had only three functions:
1. Hold off activation of the front disc brakes until 135 psi of line
pressure activated the rear drums. 2. Activate the differential pressure
switch if one system lost pressure; and, 3. Provide a convenient place for
all the plumbing to come together. My subsequent experience has seemed to
verify that, so I don't know what more a disc/disc valve does -- can
someone enlighten me? If there's not another function, perhaps more folks
will want to merely "rebuild" and modify their OEM disc/drum valve IAW this
example:
http://www.gmcmhphotos.com/photos/g3510-deciphering-the-combination-valve.html
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI & EBL,
Manny Brakes & 1-Ton, Troy-Bilt APU, etc., etc., etc.
www.gmcwipersetc.com
It was always my understanding those valves also perform a brake bias function as well.... That's what I was most concerned about. Unless the disc conversion was designed with calipers that mimicked the hydraulic requirements of the drums, the brake bias would be off unless a change to the proportioning valve was also made....
I inherited my disc conversion from the PO, so not sure if it was designed with this in mind, or if a different combination valve was used when the disc conversion kit was installed...
Mark S. '73 Painted Desert,
Manny 1 Ton Front End,
Howell Injection,
Leigh Harrison 4bag and Rear Brakes,
Fort Worth, TX
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