| Re: [GMCnet] Correct (and hopefully NON-leaking) brass combination valve? [message #358699 is a reply to message #358697] |
Wed, 16 September 2020 18:08   |
LarryInSanDiego
Messages: 336
Registered: September 2006
Karma:
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Senior Member |
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Hi, Ken.
IIRC, drums (or the drum side of a disc/drum system) combination valves
also have a residual (?) valve, retaining 2-10 psi in the line to prevent
excessive piston, and consequently, shoe retraction when brakes are
released. This also may complement the metering function you first
described.
Prior to dual systems beginning in '67 (???), single master cylinder system
drum/drum systems probably had nothing more than that metering valve built
into the single master cylinder.
Thank you.
Larry Engelbrecht
On Wed, Sep 16, 2020 at 3:52 PM Ken Henderson
wrote:
> My 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
>
>
> On Wed, Sep 16, 2020 at 6:26 PM Larry Engelbrecht via Gmclist gmclist@list.gmcnet.org> wrote:
>
>> Thanks to all for the advice. I did order one from Highway Stars. Not
>> cheap, but I hate redoing things so that peace of mind alone makes it worth
>> the
>> price.
>> --
>> Larry Engelbrecht
>>
>> San Diego, CA
>>
>> '73 26' ex-Glacier
>>
>> TZE063V100319 03/07/73
>>
>> _______________________________________________
>> GMCnet mailing list
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>
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Larry Engelbrecht
San Diego, CA
'73 26' ex-Glacier
TZE063V100319 03/07/73
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