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Old 07-30-2021, 01:14 PM
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Default Is brake proportioning valve needed?

I have a 66 LeMans with 4 wheel drum brakes. I installed a 67 Pontiac dual master cylinder and all 4 new wheel cylinders. I can't seem to bleed the brakes and a friend suggested that I needed a proportioning valve I'm looking for suggestions.

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Old 07-30-2021, 01:36 PM
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Are you saying that you continue to get air bubbles from your bleeder valves (i.e., you're unable to bleed the air out), or that you have a soft brake pedal but are not seeing any air bubbles when bleeding?

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Old 07-30-2021, 02:54 PM
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You don’t need a proportioning valve with 4 wheel drum.
I went from power brakes with a single master to manual brakes with a duel master with 4 wheel drum on my ‘66 Catalina and had no problems. Much better actually. I just gravity bleed until the fluid runs clear without any bubbles.

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Old 07-30-2021, 03:24 PM
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I don't have any pedal whatsoever. When I use that power bleeder (YSTOOL Brake and Clutch Fluid Pneumatic Vacuum Bleeder Bleeding Tool Kit) then I get some fluid but mostly air.
Not sure where to go from here.

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Old 07-30-2021, 03:40 PM
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Assuming your brakes were fine prior to the MC change, I doubt your p valve is the issue. I have had bad MCs right out of the box, and is the first place I would look.

I assume you bench bled the MC and it appeared to work fine? Assuming yes, I would then get a helper and try to bleed lines the old fashioned way with 2 people. One presses the brake pedal while the other opens and closes the bleeder valves, one wheel at time until the air is out.

Don't let the MC get too low on fluid, and be sure the bleeder is closed before your helper let's up on the brake pedal each time.

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Old 07-31-2021, 11:46 AM
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Quote:
Originally Posted by misterp266 View Post
You don’t need a proportioning valve with 4 wheel drum.
I just want to chime in and reiterate that you don't need a proportioning valve with 4 wheel drums. The proportioning takes place as a result of the wheel cylinder diameters.

I also went from the single pot system to a dual m/c on my '63 GP, with no issues.

K

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Old 07-31-2021, 08:15 PM
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Quote:
Originally Posted by Keith Seymore View Post
I just want to chime in and reiterate that you don't need a proportioning valve with 4 wheel drums. The proportioning takes place as a result of the wheel cylinder diameters.

I also went from the single pot system to a dual m/c on my '63 GP, with no issues.

K
Thanks Keith. That solidifies what I suspected and confirmed by knowledgeable people.

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