Author Topic: Eliminating the GM Proportioning Valve  (Read 678 times)

Offline slideways

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Eliminating the GM Proportioning Valve
« on: September 18, 2019, 07:19:20 PM »
I'd like to do away with the nonsense crossmember mounted prop valve while im restoring my 83 K10. I'll still be using the stock brakes but my plan is to run the front line into a T fitting directly to each caliper. Since the rear will apparently have too much power i'll use an adjustable bias knob to back it off directly to the hose on the axle out back. Im also reading i should use a 10lb residual check valve near the MC for the rear so they have fast pressure.

Does this sound like it will work? And im also verifying the stock GM MC doesnt have a residual pressure valve built into it so im not putting a second valve in for no reason.

Offline JohnnyPopper

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Re: Eliminating the GM Proportioning Valve
« Reply #1 on: September 18, 2019, 07:24:50 PM »
Can't say...

Where are you getting your info from?
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline Irish_Alley

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Re: Eliminating the GM Proportioning Valve
« Reply #2 on: September 19, 2019, 07:20:43 AM »
why not just replace the OEM one instead of rigging a something serious like the brakes?
If you can’t tell yourself the truth, who can you tell it to?~Irish_Alley

When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes

Offline slideways

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Re: Eliminating the GM Proportioning Valve
« Reply #3 on: September 19, 2019, 08:13:29 PM »
I wouldnt call it "rigging" by any means. But from seeing the ridiculous location of it when i tore the truck apart and reading all of the nightmares people have with the reset pins and springs inside, trouble bleeding, no brake pressure at certain times, the needless warning light attached to it. I would rather just mount a wilwood unit up next to the MC with an adjuster knob so i can control how much rear brake i want and have everything accessible from a standing point in the engine compartment not tucked up under the fan shroud on a piece of C Channel where you cant get wrenches and expect to get rained fluid on. This will also allow me to have one solid seamless piece of tubing from the MC area to each caliper and then also to the rear axle with no joints to leak.

I just wanted to know if anyone was knowledgeable enough whether the stock MC had a residual valve in it or if i needed the $29 10lb one for the rear. Or if there was anything else i was missing in trying to outsmart the system here.

Offline ehjorten

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Re: Eliminating the GM Proportioning Valve
« Reply #4 on: September 20, 2019, 08:20:15 AM »
Interesting.  I have never had any of these issues with the stock combination valve.
-Erik-
1991 V3500 - Gen V TBI 454, 4L80E, NP205, 14 bolt FF, D60, 8" Lift on 35s
1977 K20 Silverado - 350, THM350, NP203, 14 bolt FF, D44, Stock Lift on 31s
1969 Chevelle Malibu Sport Coupe - EFI350, THM350
1968 Chevrolet Step-side Pickup - 300HP L6

Offline philo_beddoe

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Re: Eliminating the GM Proportioning Valve
« Reply #5 on: September 20, 2019, 10:49:23 AM »
Interesting.  I have never had any of these issues with the stock combination valve.

thats because its stock, never issues with stock/oem.

ps i have a few parts on my truck that are not stock/oem. but im getting there.
Behold, the day of the LORD cometh, and thy spoil shall be divided in the midst of thee.  Zechariah 14:1

Offline JohnnyPopper

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Re: Eliminating the GM Proportioning Valve
« Reply #6 on: September 20, 2019, 01:00:01 PM »
I agree with your pain points, pretty poor location.

So I wondered where you were getting your info from and I just saw a Wilwood ad in a C-10 mag!

It looks interesting, though they still say it's a proportioning valve...?

I want to call them to see just how the adjustment valve comes into play.
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline bd

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Re: Eliminating the GM Proportioning Valve
« Reply #7 on: September 20, 2019, 01:17:01 PM »
To help round out the picture, read through Brake Valve Overview authored by Master Power Brakes.  By eliminating the OE combination valve you will lose both the convenience of a compact, well-integrated component and the vital safety feature of the pressure differential valve.  Of course, you can duplicate the various aspects of the combination valve, but at greater cost, sacrifice of space and increased complexity with regard to mounting and plumbing.  Consider this: of all the vehicles on the road that employ brake combination valves, relatively few experience valve failures, although the valves are often falsely blamed.  It's just that the few that fail or are suspected of failing receive a lot of notoriety because their simple function is mysterious to most people.

As far as the residual check valve is concerned, IIRC that function is assumed by the metering section of the combination valve.  As long as you incorporate a new metering valve along with the proportioning valve, you are unlikely to feel a lag in brake application or the introduction of air contamination drawing past the wheel cylinder cups due to fluid evacuation during a sudden release of application pressure.
Rich
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In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline JohnnyPopper

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Re: Eliminating the GM Proportioning Valve
« Reply #8 on: September 21, 2019, 05:59:56 AM »
That was a great read BD, I feel smarter about brakes now, in fact, I'm never going to b***h about my combo/proportioning valve ever again except when I have to work on it- like centering the pin so the stinking light will go out...

Reminds me of working on a Rolls Royce, circa 1979, had FOUR master cylinders, one for each wheel!

So we (shop crew) theorized that the Brits imagined that in a catastrophic failure, as in losing 3 of your wheels, you still had a prayer of coming to a stop.

Britannia rules the waves...
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline VileZambonie

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Re: Eliminating the GM Proportioning Valve
« Reply #9 on: September 21, 2019, 06:32:44 AM »
Look at how the later model RWAL system was setup (like a 91 burb). Sounds like all you need is a donor to set it up the way you want.
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