Quote:
Originally Posted by chuckies76ta
I used this unit on my wife's 68 Firebird and the brakes worked very well. That valve is called a Proportioning Valve.
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NO. The guy who wrote the sheet you've linked-to is WRONG. It is NOT a "proportioning valve", it's a Metering valve, or Holdoff valve.
Quote:
Originally Posted by chuckies76ta
There should be no leakage from any component on a breaking system.
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Correct. That leaking valve assembly is defective. GM says they're non-repairable, but I figure (almost) anything that can be made, can be taken apart and re-made. (If you can get repair parts.)
Quote:
Originally Posted by chuckies76ta
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The description is generally correct except for the bold print claiming it's a "PROPORTIONING VALVE".
Quote:
Originally Posted by chuckies76ta
Do not fear, although the service manual says to "press" the button when bleeding, this is a misprint in the service manual.
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NO, that is NOT a misprint. The button is to be pressed--holding it in place--when the FRONT brakes are being bled using moderate pressure as might be encountered with a pressure bleeder. You would not need to dick with the metering valve when bleeding with zero pressure as in gravity bleeding, or with high pressure as with "pump-the-brake-pedal" bleeding.
This part functions in a three-phase system. With zero or very slight pressure, the valve does not block fluid flow. The brake system beyond the valve is allowed to vent into the master cylinder reservoir based on temperature change. The brake fluid expands when hot, it has to vent to the reservoir to avoid applying the brakes especially disc brakes.
As you apply the brake pedal, the rear drums need enough pressure to overcome the tension of the shoe return springs. This valve blocks low pressure to the front brakes, so that the rears can develop that minimum pressure to move the shoes.
Finally, as the pressure continues to increase, the valve is 'blown open" allowing full pressure to the front brakes so they apply more-or-less simultaneously with the rears.
As a result, trying to bleed brakes using that somewhat-low pressure that is enough to cause the valve to block flow to the front brakes, you'll get no fluid flow--so you'd have to force the valve back to it's "vent" position; or pull it out to it's "blown open" position to get flow.
THAT'S THE THEORY. In actual use, I have NEVER needed to dick with the Metering/holdoff valve to bleed front brakes. I do not own the tool to push or pull the metering valve stem. I pressure bleed at no more than 15 psi, and more-often at about 10 psi. Apparently, that's not enough pressure to cause the Metering valve to block flow.
Quote:
Originally Posted by kyle_blake
I read the last link where shurkey mentioned that that you need more than 10 psi to bleed it with a power bleeder.
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Nope. I bleed at around 10-15 psi when I use a pressure bleeder. HIGHER pressure MIGHT require playing games with that metering valve stem. Most of the time, I gravity-bleed.
Quote:
Originally Posted by kyle_blake
I hope the next valve works . Feel like hooking a line up when I pick it up and putting dot 3 in it and seeing if it gravity bleeds through before even taking it home.
I mean it had to be defective , i'm sure pressing the pedal car not running and the valve not letting anything through is more than 10 psi. should of just returned it then.
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Yup, that valve seems to be doubly-defective.
1. It leaks, and
2. It blocks fluid flow all the time.