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#1 |
Registered User
Join Date: Apr 2010
Location: So Cal
Posts: 1,437
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Re: Proportioning Valve Keeps Tripping?
He stated that he is using the speed bleeders. They come with a thread coating, although this coating could have deteriorated. A common problem with vacuum bleeding is sucking air past the bleeder threads unless the threads are wrapped.
He also said he has tried a pressure bleater. I could see a problem with manual bleeding, if debris is holding the Speed Bleeder Valve open and the valve is not closed, each time the pedal is withdrawn. This wouldn't affect vacuum or pressure bleeding. My only conclusion from all of the above postings is that the Primary Section of the MC has failed.
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'67 GMC 2500, 292, 4spd, AC |
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#2 |
Senior Member
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Location: San Ramon,CA
Posts: 504
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Re: Proportioning Valve Keeps Tripping?
You could always let it gravity bleed :shrug:
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1970 C10 Custom longbed 350/350 |
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#3 | |||||
Senior Member
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Location: Toano, VA
Posts: 874
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Re: Proportioning Valve Keeps Tripping?
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I have tried this as well. Still no dice unfortunately.
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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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#4 |
Senior Member
![]() Join Date: Jul 2000
Location: North Texas
Posts: 3,488
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Re: Proportioning Valve Keeps Tripping?
Might be a PITA to bypass the combination valve with temporary hard lines, but that would probably tell you where the problem is. Of course you would need the proper bending and flaring tools, along with fittings.
Is still don't see the problem being a wheel cylinder or something else "sucking in" air.
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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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#5 |
Registered User
Join Date: Jan 2007
Location: Topeka,KS
Posts: 778
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Re: Proportioning Valve Keeps Tripping?
Have you tried adjusting the push rod between the the boostewr and master cylinder
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68' C20. 283CI w/55CC 305HO heads, NP435 Close Ratio, Corp. 14 bolt FF 3.21, 75' front end swap (everything but the X-member). |
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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?
UPDATE 3/28/24
I replaced the wheel cylinders for the rear axle, and the fluid is coming out completely air free now. I ran a ton of fluid to be sure with a pressure bleeder for extra insurance. The pedal feels more solid at this time. NOW, I am having a brake light come on the dash past 3/4 pedal travel. BUT, when this happens, when I bring the pedal back up past that area, it clears itself. So I am thinking I have or may be dealing with separate issues. Possibly the MC bypassing itself? I at this point get sick at the idea of bleeding brakes. LOL. Any further pointers or ideas?
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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: 3,488
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Re: Proportioning Valve Keeps Tripping?
Quote:
That shuttle valve is acting very strange. Could it be moving to the front? Are the front calipers installed with the bleeder screws on the top?
__________________
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
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Location: Toano, VA
Posts: 874
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Re: Proportioning Valve Keeps Tripping?
Quote:
I am curious - when the cap is off the master cylinder, and I press the brake pedal, there is a bit of brake fluid that 'shoots' up, to the point I just put a rag over it so it doesnt get all over the place. Maybe a few inches, is this an indication of anything?
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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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#9 |
Senior Member
![]() Join Date: Jul 2000
Location: North Texas
Posts: 3,488
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Re: Proportioning Valve Keeps Tripping?
That's normal. Kinda like a miniature Old Faithful!
__________________
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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#10 |
Senior Member
![]() Join Date: Jul 2000
Location: North Texas
Posts: 3,488
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Re: Proportioning Valve Keeps Tripping?
If you have an ohmmeter, remove the brake warning switch, then set it on a workbench and check to see how sensitive it is. As I mentioned in a post above, the brand new one I bought would close (zero resistance) when the pin barely moved -- around .050". It could be that yours has a similar problem, so even when the pressure differential valve moves just a tiny bit, the pin moves up and closes the switch.
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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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#11 | |
Senior Member
![]() Join Date: Mar 2014
Location: Toano, VA
Posts: 874
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Re: Proportioning Valve Keeps Tripping?
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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#12 |
Registered User
Join Date: Apr 2010
Location: So Cal
Posts: 1,437
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Re: Proportioning Valve Keeps Tripping?
>>should be pedal be harder/more firm with the booster set up when the motor is running?<<
Pump the pedal a couple of times and HOLD. You should have a very high, firm pedal. Start the engine. As vacuum builds, your foot and pedal will drop. The booster is designed to hold vacuum for 3 applications of the pedal. If the engine dies while driving, the booster should hold plenty of vacuum to give vacuum assist in order for you to get to the side of the road. Turn the engine off. Apply the brakes 3 times. The pedal should be higher and firmer after each successive application.
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'67 GMC 2500, 292, 4spd, AC |
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#13 |
Senior Member
![]() Join Date: Mar 2014
Location: Toano, VA
Posts: 874
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Re: Proportioning Valve Keeps Tripping?
Well, heres an update again.
Pedal gets firm about 1/4 down, and feels OK when engine is OFF. But, when its running, its like its a 100% dry system. Put in gear (on jack stands) and brakes have zero effect in the rear, fronts I havent checked since I didnt have it actually move. I am at a huge loss right now because I have literally bled gallons through this system. Now I am thinking the MC is bad. Thoughts?
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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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#14 |
Registered User
Join Date: Apr 2010
Location: So Cal
Posts: 1,437
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Re: Proportioning Valve Keeps Tripping?
post #34
>>My only conclusion from all of the above postings is that the Primary Section of the MC has failed.<<
__________________
'67 GMC 2500, 292, 4spd, AC |
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#15 |
Senior Member
![]() Join Date: Jul 2000
Location: North Texas
Posts: 3,488
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Re: Proportioning Valve Keeps Tripping?
Do you have the tools, brake line, and fittings to bypass the combo valve? It may possible that the proportioning valve is limiting pressure to the rear WAY before it's supposed to.
Then again it might be a bad M/C like Richard says. Bypassing the combo valve will tell you where the problem is, or isn't.
__________________
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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#16 |
Senior Member
![]() Join Date: Jun 2022
Location: San Ramon,CA
Posts: 504
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Re: Proportioning Valve Keeps Tripping?
On old earth moving equipment, they'd sometimes use an oil can clamped to a hose to bleed hydraulic systems from the lowest point back to the reservoir.
You might try this with a big syringe from the farthest wheel cylinder. Looking for flow, and maybe trapped air. This way is messy, so rig up a drip pan and wash off any spilled fluid in the engine compartment Otherwise, I agree with the above and you'll have to get clever with swapping parts or plumbing to isolate the problem
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1970 C10 Custom longbed 350/350 |
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#17 | |||
Senior Member
![]() Join Date: Mar 2014
Location: Toano, VA
Posts: 874
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Re: Proportioning Valve Keeps Tripping?
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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#18 |
Senior Member
![]() Join Date: Mar 2014
Location: Toano, VA
Posts: 874
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Re: Proportioning Valve Keeps Tripping?
UPDATE 4/3/24
I ordered a new proportioning valve to swap out in case this ends up being an issue - it has solved the brake light issue, but the brakes are only at the bottom of the pedal. I have ensured a 1/16 clearance to the MC from the booster, and that is proper. I am in the camp that the MC is bad. That will probably be my next item to replace.
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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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#19 |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,602
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Re: Proportioning Valve Keeps Tripping?
Might be the only thing wrong with the master is it’s bore is too big.
Measure it first. And did you change your pedal ratio? Last edited by geezer#99; 04-03-2024 at 09:23 PM. |
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#20 |
Senior Member
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Location: Toano, VA
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Re: Proportioning Valve Keeps Tripping?
The bore is 1", I would imagine that isnt a problem given this is a 'kit' set up to work with each other. The pedal ratio was slightly modified, but pushing the pedal in and out, I dont see any issue with the travel.
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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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#21 |
Registered User
Join Date: Aug 2009
Location: Bowser
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Re: Proportioning Valve Keeps Tripping?
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#22 | |||||
Senior Member
![]() Join Date: Mar 2014
Location: Toano, VA
Posts: 874
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Re: Proportioning Valve Keeps Tripping?
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I normally do the one man method, but I cant even get a small amount of fluid from the rear. Its mind boggling. Even punching the pedal does nothing. I figured a pressure rush would at least make it do something, but nothing at all. 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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#23 |
Senior Member
![]() Join Date: Mar 2014
Location: Toano, VA
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Re: Proportioning Valve Keeps Tripping?
Well, I ordered a new master cylinder last night. After that, Im all out of ideas. We will see!
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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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#24 |
425hp409
![]() Join Date: Oct 2008
Location: Prosper Texas
Posts: 841
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Re: Proportioning Valve Keeps Tripping?
Some service manuals said to lightly tap the caliper with a hammer to dislodge any small air bubbles that may be clinging to the caliper wall. This could be your pressure differential problem. This was in the textbook that I used when I taught at a trade school.
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Charles 68 SWB, Dad bought new, now 396 & factory ac 64 Impala SS, 409 425HP, 4 speed AC 64 Bel Air Wagon, 400 Small Block 57 Bel Air all original 283 w/Factory Air 77 GMC Sprint, 454/425HP 67 Olds 442, all original 90 ZR1 Corvette |
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#25 | |
Senior Member
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Location: San Ramon,CA
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Re: Proportioning Valve Keeps Tripping?
Quote:
Could still be air in those wheel cylinders somehow, but I don't know if it can hide the way it might in a caliper.
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1970 C10 Custom longbed 350/350 |
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bleeding, brake light, brakes, proportioning valve |
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