Home » Public Forums » GMCnet » Correct (and hopefully NON-leaking) brass combination valve? (GM 1257177 / AC Delco 172-1350?)
| Correct (and hopefully NON-leaking) brass combination valve? [message #358587] |
Mon, 14 September 2020 00:25  |
LarryInSanDiego
Messages: 336
Registered: September 2006
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I've been reading about brass combination valves that leak, supposedly the Chinese-made PV2 (I have the stock disc/drum setup and original iron combination valve). Seems the GENUINE GM 1257177 is nearly impossible to find, and many of the hits when I enter "AC Delco 172-1350" actually say words to the effect that it's made "identical to", or "AC Delco TYPE" (caps mine), which doesn't convincingly sound like a genuine AC Delco part. I've also read on this board that one of the fittings strips easily, so I'm understandably hesitant to figure out exactly which one to purchase.
Are all the PV2s leakers? I did find one source claiming its part is made by AC Delco, so that seems to be the safest bet at this point, but I'd like to hear what the community says.
Any advice? Thanks in advance.
Larry Engelbrecht
San Diego, CA
'73 26' ex-Glacier
TZE063V100319 03/07/73
[Updated on: Mon, 14 September 2020 12:26] Report message to a moderator |
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| Re: Correct (and hopefully NON-leaking) brass combination valve? [message #358678 is a reply to message #358676] |
Tue, 15 September 2020 18:06  |
SpookyEng
Messages: 208
Registered: June 2016
Location: Navarre, FL
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Bill Van Vlack wrote on Tue, 15 September 2020 17:15The description indicates that it is for '4-wheel disk brakes'.
This part?
Brand-new solid brass discontinued new-old-stock genuine GM Brake Combination Valve for various GM front disc/rear drum brake applications.
GM # 1257177 ACDelco # 172-1350
We are aware that this brake valve fits 1973-1978 GMC Motorhomes Vin TZE, and also 1974 Super Duty (SD) 455 Trans Am.
JD Lisenby- USAF Ret
1978 Royale-455
MacDash, Manny Tranny, FI-tech, 3.70 etc etc
Navarre, FL
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| Re: Correct (and hopefully NON-leaking) brass combination valve? [message #358688 is a reply to message #358587] |
Wed, 16 September 2020 08:59 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Highway Stars is my friend’s company. Bob Stone was having multiple issues with the Chinese PV2s. So as an ACD dealer I had Highway Stars source them in system and buy them up for him. We put the remaining units on the Highway Stars web site. GM /ACD new in box. This also crosses to the 74 SD455 Trans Am which was Disc /Drum before they went all disc. Bob gave us the part numbers to source these. And yes the PV2 MBM parts are also sold on his page for the Regal crowd so be sure NOT to click on any of those.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] Correct (and hopefully NON-leaking) brass combination valve? [message #358697 is a reply to message #358696] |
Wed, 16 September 2020 17:51 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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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
> Unsubscribe or Change List Options:
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| 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
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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
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>
>
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Larry Engelbrecht
San Diego, CA
'73 26' ex-Glacier
TZE063V100319 03/07/73
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| Re: [GMCnet] Correct (and hopefully NON-leaking) brass combination valve? [message #358701 is a reply to message #358698] |
Wed, 16 September 2020 18:40 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Well, I did get to learn at least one thing today! I didn't even think
about the 2 psi "hold on" pressure for the discs -- thinking back, that's
probably a second purpose for the little relief valve actuated by the pin
on the front of the combination valve. But the only "Brake Light" I can
find actuated by the differential pressure switch is that connected to pin
E on the instrument cluster -- not those on the rear of the coach, which is
what I first thought John was telling us about. But John's right about
that being a second function because the REALLY important one is shutting
off the non-functional brake system to limit fluid loss -- IIRC.
Ken H.
On Wed, Sep 16, 2020 at 7:12 PM John R. Lebetski via Gmclist <
gmclist@list.gmcnet.org> wrote:
> Ken on #2 besides toggling the valve if one side fails it also grounds the
> brake light to come on. So 2 is really 2 things if that’s what you meant.
>
> Also to comment on the price from the other post, he’s selling below.
> MSRP.
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
>
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| 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: -7
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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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| Re: [GMCnet] Correct (and hopefully NON-leaking) brass combination valve? [message #358729 is a reply to message #358728] |
Thu, 17 September 2020 09:53 |
TR 1
Messages: 348
Registered: August 2015
Location: DFW
Karma: -7
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Senior Member |
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TR 1 wrote on Thu, 17 September 2020 09:50
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...
And I guess the 3rd option is brake bias was not even considered in designing the conversion, in which case I am just not getting full brake performance out of my system....
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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| Re: Correct (and hopefully NON-leaking) brass combination valve? [message #358734 is a reply to message #358587] |
Thu, 17 September 2020 12:40 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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I wish Bob Stone was on line here. I have to ask him but most biasing is AFAIK determined by the master. He has been measuring various MCs and coming up with interesting data. One thing is if the biasing is off or inverted, it trips the combination valve, as it is just doing it’s job.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] Correct (and hopefully NON-leaking) brass combination valve? [message #358739 is a reply to message #358692] |
Thu, 17 September 2020 16:35 |
stu@97381.com, Emery
Messages: 232
Registered: June 2020
Karma: 2
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Jim Kanomata appliergmc.com carries both the disc/drum and the disc/disc combination valves.
Emery Stora
> On Sep 16, 2020, at 12:21 PM, Mark Sawyer via Gmclist wrote:
>
> Does anyone know if this would be the same combination valve for a coach with a rear disk conversion?
> --
> Mark S. '73 Painted Desert,
> Manny 1 Ton Front End,
> Howell Injection,
> Leigh Harrison 4bag and Rear Brakes,
> Fort Worth, TX
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
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