Brake Bleeding Mystery REVEALED - Team Camaro Tech
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post #1 of 5 (permalink) Old Sep 24th, 10, 08:11 PM Thread Starter
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Join Date: Oct 2007
Location: St. Louis, MO
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Brake Bleeding Mystery REVEALED

If anyone is still interested, search for my posts about the bleeding problems I had, and all the solutions I tried.

I was attempting the less-expensive solutions first, but, as Sauron and some others suggested the sinister problem turned out to be…drum roll…the Hold-Off Valve! As soon as I replaced that with a virtually identical-looking part from Inline Tube, the front brakes bled easily and quickly—problem solved.

Now, my brakes are not as stop-on-a-dime awesome I'd hoped they'd be after all I did to the system, and I am hoping they'll improve slightly after break in, but they feel very acceptable and safe.

Thank you all for you helpful and friendly input. I replaced a lot more than I probably had to, but after 40 years, it was probably time anyways.

Wish I knew how to post a pic or two of my "finished" ride.
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post #2 of 5 (permalink) Old Sep 24th, 10, 09:14 PM
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Re: Brake Bleeding Mystery REVEALED

Corrosion is what ruins the hold-off valve. They should have made it out brass instead of cast iron.

Glad you got her fixed.
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post #3 of 5 (permalink) Old Sep 24th, 10, 10:40 PM
David Pozzi
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Re: Brake Bleeding Mystery REVEALED

Just thought I'd throw the following info in for our archives.
The hold off valve would only be needed when driving a front disc brake equipped Camaro on ice or mud, and applying the brakes lightly like at a stop light, it can be worse with an auto transmission with the choke on fast idle. With the car above on a slippery surface, applying the brakes lightly will only cause the front discs to function, there isn't enough line pressure to overcome the rear drum return spring pressure. Once above 40 PSI the rear drums will begin to work. The Hold Off Valve prevents hydraulic pressure from passing to the front discs until the 40 psi threshold is reached. The purpose of the button which is the source of leaks is to allow pressure bleeding of the front discs, the button must be held in as most pressure bleeders can't be pressurized higher than 40 psi or they would be damaged. When manual bleeding, the button does not need to be held in. By the way, it takes a special tool to hold the button in, you can't do it by hand.


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post #4 of 5 (permalink) Old Sep 25th, 10, 08:02 AM
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Re: Brake Bleeding Mystery REVEALED

Originally Posted by davidpozzi View Post
By the way, it takes a special tool to hold the button in, you can't do it by hand.

A wedge shaped doorstop or a large radiator hose clamp works. And as David said, it needs to be held in, not pushed in. At rest, it's in. This confuses a lot of people who try to push the button in, only to find it won't budge.

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post #5 of 5 (permalink) Old Sep 26th, 10, 07:47 PM
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Location: San Jose, CA.
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Red face Re: Brake Bleeding Mystery REVEALED

I would like to say "THANK YOU" for posting this thread as I have been replacing my old stock calipers w/ a bolt in Wilwood type and I have been trying to bleed them w/ a Motion Power Bleeder and was getting no where and I got a friend (Dennis~DjD) and he mentioned this thread and what both Dave P & BPOS said about the "button" and it made this part of the project go very smooth- sure I need to bleed it some more but I do have brakes!
Thanks everybody!!

Mark (AKA Z28 Mark)
1973 Z28 2001 Z28
Camaros Limited~Nor Cal
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