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#1 |
Senior Member
![]() Join Date: Mar 2014
Location: Toano, VA
Posts: 874
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Proportioning Valve Keeps Tripping?
1967 C10 - Disc conversion (power 8" booster) - master cylinder is 1" bore, and the proportioning valve was advertised when bought in the kit as a disc/drum setup.
I am having an issue with my proportioning valve. When I go to bleed the brakes, while using the proportioning valve tool to center the shuttle valve, everything bleeds fine, no leaks and good strong flow. No air coming out anymore, I did plenty of extra pedal strokes to ensure this and had no air that I could see come out. But when I put the brake switch back in, bleeders all closed, and press the pedal down half way, the red brake light illuminates. I have pulled the switch and confirmed the shuttle valve closes the rear brakes. Recenter, does it again. I confirmed the rear brake shoes are at their proper adjustment with a brake drum/shoe caliper tool to get the measurement even. Even after adjusting and all this bleeding, it seems like its either seeing a fault at the rear. So my question essentially is how do I move forward from here? From the factory, the front brakes are fed by 1 line off the front of this proportioning valve down to a T fitting split to both sides, and obviously rear is one that goes to a T on the differential. Someone did say my front feed being at the top fitting (pictured) is an issue, I don't see this as an issue being this should be able to balance it, am I incorrect?
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"Sometimes I do serve as a good bad example. Glad to be of service." My Build Thread (1967 C10, lowered, EFI, daily truck): http://67-72chevytrucks.com/vboard/s...d.php?t=830809 |
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#2 |
Registered User
Join Date: Apr 2022
Location: Moorpark, CA
Posts: 757
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Re: Proportioning Valve Keeps Tripping?
The position of front line is not the problem.
Your PV is sensing a change which triggers the switch. Whatever direction it moves, that part (front or back) has a leak you need to find ...or the PV is bad which is rare but given source of replacement parts used in these kits, way more possible now. Power brake disc typically use a 1 1/8" bore MC but that would not affect what PV is doing. larger bore just means less pedal stroke as the booster assist does not need the stroke a manual setup needs. Last edited by 72SB; 03-14-2024 at 10:35 AM. |
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#3 |
Junior Member
![]() Join Date: Apr 2021
Location: Santa Cruz, NM
Posts: 99
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Re: Proportioning Valve Keeps Tripping?
In my opinion the front brake line coming off the combination valve upwards shouldn't matter because it was designed that way for two front brake lines. However, typically when using a single line with a tee, others (factory included?) used the bottom port and plugged the top. I don't think it will matter.
Someone else, on this forum, stated that their switch was too sensitive. Are you seeing a lot of movement of the shuttle valve? Having removed the switch, how much movement can it have before the light turns on? How do you know that the proportioning valve isn't stuck in the open position? It's function is too reduce the pressure to the rear, right? What would the shuttle valve do, if the proportioning valve wasn't doing its function? I think it would slide rearward a bit. You could replace just the proportioning valve, and see if it makes a difference. Then you could disassemble the first proportioning valve to see if there was a problem. |
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#4 |
Registered User
Join Date: Apr 2010
Location: So Cal
Posts: 1,437
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Re: Proportioning Valve Keeps Tripping?
>>proper adjustment with a brake drum/shoe caliper tool <<
If you are talking about a "resetting tool" , the shoes are probably still too far away from the drums. You should adjust until the shoes drag and then step on the brake pedal to center the shoes. You have to readjust tighter, press on the brake and check for drag again. The finish adjustment should allow you to hear some drag, but not necessarily feel any resistance when you turn the drum.
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'67 GMC 2500, 292, 4spd, AC Last edited by RichardJ; 03-14-2024 at 11:16 AM. |
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#5 |
Senior Member
![]() Join Date: Mar 2003
Location: Colfax-California
Posts: 8,526
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Re: Proportioning Valve Keeps Tripping?
Which mater cylinder do you have on there? Lift the cap off and take a pic.
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#6 | |||
Senior Member
![]() Join Date: Mar 2014
Location: Toano, VA
Posts: 874
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Re: Proportioning Valve Keeps Tripping?
Quote:
Quote:
Quote:
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"Sometimes I do serve as a good bad example. Glad to be of service." My Build Thread (1967 C10, lowered, EFI, daily truck): http://67-72chevytrucks.com/vboard/s...d.php?t=830809 |
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#7 |
Senior Member
![]() Join Date: Jul 2000
Location: North Texas
Posts: 3,489
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Re: Proportioning Valve Keeps Tripping?
My almost-new switch all of a sudden got very sensitive, even when not applying the brakes. I pulled it out and checked it on the bench with an ohmmeter. Turns out that just a very small bit of upward movement causes the switch to close. I mean we're talking .050" if that much.
Ended up using the later model switch that came with my aftermarket combo valve. Unfortunately, the wire connector is different, but that's no big deal -- just another PITA to deal with. This is probably not your problem, since your switch closes only when you step on the brakes. But I just wanted to get this info out there -- the light flickering or being on all the time could indicate a bad ChiCom switch. On another note, that's a dual 8" booster, right?
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Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then! |
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#8 |
Senior Member
![]() Join Date: Jun 2022
Location: San Ramon,CA
Posts: 504
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Re: Proportioning Valve Keeps Tripping?
Maybe try adjusting the backs to be stupidly tight and see if that makes a difference.
IF you still have the differential pressure valve moving, then there's air or fluid loss somewhere causing a....pressure difference
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1970 C10 Custom longbed 350/350 |
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#9 | |
Senior Member
![]() Join Date: Mar 2014
Location: Toano, VA
Posts: 874
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Re: Proportioning Valve Keeps Tripping?
Quote:
I actually did adjust them to the point where the wheel wont turn. Still the same. I am thinking I have a huge bubble somewhere and its possibly in the rear circuit at the prop or in the prop valve.
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"Sometimes I do serve as a good bad example. Glad to be of service." My Build Thread (1967 C10, lowered, EFI, daily truck): http://67-72chevytrucks.com/vboard/s...d.php?t=830809 |
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#10 | |
Senior Member
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Location: San Ramon,CA
Posts: 504
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Re: Proportioning Valve Keeps Tripping?
Quote:
Bought a pack of these off the River :shrug:
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1970 C10 Custom longbed 350/350 |
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#11 |
Senior Member
![]() Join Date: Mar 2014
Location: Toano, VA
Posts: 874
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Re: Proportioning Valve Keeps Tripping?
Ive thought of this as well when I was bench bleeding the MC. That may be on the list after some abrupt pressure bleeding.
__________________
"Sometimes I do serve as a good bad example. Glad to be of service." My Build Thread (1967 C10, lowered, EFI, daily truck): http://67-72chevytrucks.com/vboard/s...d.php?t=830809 |
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#12 |
Registered User
Join Date: Jul 2018
Location: Catskill Mountains,NY
Posts: 8,476
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Re: Proportioning Valve Keeps Tripping?
When the light goes on do the rear brakes still actuate? The proportion valve when tripped will stop the fluid from going to that circuit. I would let the light come on and try to bleed the rear brakes no fluid the circuit is tripped if you get fluid then it may be the switch .
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Mark 72 c20 custom camper Husky edition, 66 SS396 Chevelle 1964 Hawk, 63 Avanti,62 lark 1969 AMX , 1968 c20 stepside ,85 K20 1977 Suburban sold 68 anniversary. |
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#13 | |
Senior Member
![]() Join Date: Jul 2000
Location: North Texas
Posts: 3,489
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Re: Proportioning Valve Keeps Tripping?
Quote:
Have you bled brakes in the past? Are you shutting the bleeder valve before your helper lets off the pedal? And/or submerging the bleeder hose in fluid so it can't suck in air?
__________________
Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then! |
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#14 | |
Senior Member
![]() Join Date: Mar 2014
Location: Toano, VA
Posts: 874
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Re: Proportioning Valve Keeps Tripping?
Quote:
![]() As far as pedal feel, it is soft sometimes, and sometimes when bleeding it is hard. Counterintuitive.
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"Sometimes I do serve as a good bad example. Glad to be of service." My Build Thread (1967 C10, lowered, EFI, daily truck): http://67-72chevytrucks.com/vboard/s...d.php?t=830809 Last edited by KyleSeal; 03-14-2024 at 03:51 PM. Reason: addt'l info |
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#15 |
Senior Member
![]() Join Date: Feb 2009
Location: Northern Nevada
Posts: 7,237
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Re: Proportioning Valve Keeps Tripping?
Old school reputable mech. says old CPV vales rarely fail.
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Tony 71 Custom Deluxe, SWB, 2WD, 402, A/C. I developed an assembly kit for restoring the (a) truck from the ground up. My build thread, and more on the assembly kit https://67-72chevytrucks.com/vboard/...d.php?t=730025 |
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#16 |
Senior Member
![]() Join Date: Mar 2014
Location: Toano, VA
Posts: 874
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Re: Proportioning Valve Keeps Tripping?
The plan as of now;
1. I purchased a pressure bleeder, should be here Saturday. I will force all the air and fluid out with it if theres any. If no avail; 2. I will replace the master and proportioning valve with a 1-1/8" master kit. If no avail; 3. I will start going to church ![]() Does anyone think the dual-diaphragm 8" booster with a 1" bore master is an issue? I am not thinking it is as I dont know why one would be sold if that was the issue, but now I am possibly beginning to second guess all components.
__________________
"Sometimes I do serve as a good bad example. Glad to be of service." My Build Thread (1967 C10, lowered, EFI, daily truck): http://67-72chevytrucks.com/vboard/s...d.php?t=830809 |
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#17 |
Registered User
Join Date: Apr 2022
Location: Moorpark, CA
Posts: 757
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Re: Proportioning Valve Keeps Tripping?
I did my 72 manual disc/drum to power using the CPP booster/mc/pv. Rears went to rear of PV, front to front of PV. (pic)
O{, I think your issue is the PV or the shuttle switch in it. OP, power front disc brakes use a 1 1/8" MC. Manual drum uses 1" MC. Either should "work" but with the 1 1/8 MC the pedal stroke will be shorter which with the booster is all that is needed. |
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#18 |
Senior Member
![]() Join Date: Jul 2000
Location: North Texas
Posts: 3,489
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Re: Proportioning Valve Keeps Tripping?
As for bleeding an M/C, I do it on the truck using these hard lines. Surprisingly, not a lot of fluid leaks out when you remove them after bleeding. Sure beats doing it using those M. Mouse kits that come with some M/Cs.
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Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then! |
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#19 |
Senior Member
![]() Join Date: Jun 2022
Location: San Ramon,CA
Posts: 504
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Re: Proportioning Valve Keeps Tripping?
I rigged up one of these from the old lines(after I lost the plastic pieces that came with the MC). I prolly would have never bothered with syringe bleeding had I known at the time that thrashing on the brakes creates thousands of tiny bubbles through cavitation, as does applying stupid heavy vacuum
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1970 C10 Custom longbed 350/350 |
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#20 |
Junior Member
![]() Join Date: Apr 2021
Location: Santa Cruz, NM
Posts: 99
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Re: Proportioning Valve Keeps Tripping?
I like Mike B's master cylinder bleeder lines. I was thinking about a tee off the proportioning valve port with a bleeder screw, or straight to a bleeder screw with an adapter (if manufactured), or a tube nut with hard line and vinyl hose. Isn't there a brake line coupler on the frame rail? Maybe you could bleed from there also. I think you're right, it's more likely that you have an air bubble near the start of the rear brake line. Good luck.
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#21 |
Senior Member
![]() Join Date: Mar 2014
Location: Toano, VA
Posts: 874
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Re: Proportioning Valve Keeps Tripping?
This weekend I tried the power bleeder. No dice.
I am beginning to believe I am pulling air, but not leaking fluid. I have heard numerous times now about wheel cylinders bringing mystery air in. These wheel cylinders are probably 8 years old, never used. That being said, I never had fluid in the system to test them. I am going to replace them and recheck. Everytime I go to bleed the rears, I get micro bubbles and sometimes very small ones, but regardless I get a stream every time I open the bleeder. I ran nearly a gallon of fluid through them and still had the same situation. I also rebled the master cylinder to ensure no air is trapped in it, and it bled clean.
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"Sometimes I do serve as a good bad example. Glad to be of service." My Build Thread (1967 C10, lowered, EFI, daily truck): http://67-72chevytrucks.com/vboard/s...d.php?t=830809 |
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#22 |
Registered User
Join Date: Jul 2008
Location: Eastern Oregon
Posts: 2,336
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Re: Proportioning Valve Keeps Tripping?
Kyle I applaud your persistence ! Keep at it ! Lots of people will learn from your experience..Jack
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71 C-20 07 Magnum RT AWD |
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#23 | |
Senior Member
![]() Join Date: Jul 2000
Location: North Texas
Posts: 3,489
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Re: Proportioning Valve Keeps Tripping?
Quote:
FYI, if you are pulling fluid trough the bleeder valves using a vacuum pump like a MityVac, you will almost always see bubbles from air creeping in between the hose and bleeder valve.
__________________
Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then! Last edited by MikeB; 03-18-2024 at 05:52 PM. |
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#24 |
Senior Member
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Location: Cypress, TX
Posts: 3,703
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Re: Proportioning Valve Keeps Tripping?
What are the full specs for the kit, or webpage where it is sold?
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#25 |
Registered User
Join Date: Apr 2022
Location: Moorpark, CA
Posts: 757
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Re: Proportioning Valve Keeps Tripping?
It is not uncommon to pull air from bleeder nipples being loosened to bleed at the threads. A thin coat of silicone on the bleeder nipple threads prevents this. Do not use Teflon tape.
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bleeding, brake light, brakes, proportioning valve |
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