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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 #367168 is a reply to message #367164] Mon, 11 October 2021 20:17 Go to previous messageGo to previous message
jimk is currently offline  jimk   United States
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma:
Senior Member
The shipment from China that Tom P. has tested should arrive this week and
will be available and will have an Identifying mark.
I am as leary as anyone on a product made there, but who else will do few
hundred at affordable price?
I will soon find out.

On Mon, Oct 11, 2021 at 1:56 PM Ken Henderson
wrote:

> Emory,
>
> Either your age is showing, or mine's about to!: IIRC, the combination
> valve PREVENTS pressure from reaching the front brakes until the rears
> receive about 135 psi. The purpose being to take up the free play in the
> rear drums before the fronts engage. After reaching that point, the front
> and rear brakes soon receive the same pressure. With all disc brakes, that
> delay function is not required and should not be in the "proportioning"
> valve -- which really keeps only the distribution and system monitor
> functions. This may help some to understand how it works:
>
> http://www.gmcmhphotos.com/photos/g3510-deciphering-the-combination-valve.html
>
> Ken H.
>
> On Mon, Oct 11, 2021 at 3:44 PM Emery Stora via Gmclist gmclist@list.gmcnet.org> wrote:
>
>> That looks like the valve that I put on years back. I checked mine out
>> some time back and it didn’t need a modification.
>> I don’t think that you could lock up the fronts before the rears if you
>> had the modification or not.
>> If I were you I would not do anything to it. If your brakes are working
>> now I would not mess with the valve.
>>
>> By the way it really isn’t a proportioning valve. It should be properly
>> called a combination valve. It puts a small amount of pressure on the
>> front brakes before it puts the full pressure to both the front and read.
>> It does not proportion any pressure to either the front or rears.
>> It also has a shuttle inside it which will turn on a light on the dash
>> telling you if there is no pressure on either the front or rear. This is
>> to tell you that you might have a leak in the system or low fluid on the
>> front or rear.
>>
>> Emery Stora
>> emerystora@mac.com
>>
>>
>>
>>> On Oct 11, 2021, at 12:14 PM, Russell Keith
>> wrote:
>>>
>>> So, is this the wrong combination valve?, Which I installed a few years
>> ago. I see the PV2 / 12M86 part number. If I do the modification, am I
>> more
>>> likely to flat-spot the rears before the fronts lock up? The brakes
>> "appear" to be fine now, but perhaps I don't know any better. :roll:
>>>
>>>
>>
> http://www.gmcmhphotos.com/photos/data/7010/medium/Combination_Valve2.jpg
>>>
>>>
>>> --
>>> Russell Keith,
>>> 1978 E2 "Harry" 403 (still carbureted), Danny Dunn Tranny, Thorley,
>> Stock Brakes w/Remote Vacuum Brake Booster, Quad Bags, Dakota Digital
> Dash,
>> 6.5 kW
>>> Onan, Dunedin, Florida
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--
Jim Kanomata ASE
Applied/GMC, Newark,CA
jimk@appliedairfilters.com
http://www.gmcrvparts.com
1-800-752-7502
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Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502

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