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Discussion Starter #1
The recent thread discussing the Motive Brake Bleeder got me thinking about the hold off valve on my '69. I've never had a problem bleeding the front brakes without depressing the button on the back of the valve. I see evidence of leakage at the rear line connection of my valve, but it's the original valve so who knows when that occurred. Here are my questions:
(1) Do these valves go bad and if so how do you know?
(2) The button on the back of my valve doesn't seem to move at all when I press it. Do you actually feel it depress when you push on it? (maybe mine is stuck in the depressed position which is why its easy to bleed my front brakes)
(3) Should the button be easy to depress or is it pretty hard? (given its location, I'd hope it wouldn't be too hard or you'd never be able to push it in without unbolting the valve first)
(4) To bleed the front brakes do you press the button once or does it have to be held in the depressed position as the brakes are bled?

Thanks.
 

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The recent thread discussing the Motive Brake Bleeder got me thinking about the hold off valve on my '69. I've never had a problem bleeding the front brakes without depressing the button on the back of the valve. I see evidence of leakage at the rear line connection of my valve, but it's the original valve so who knows when that occurred. Here are my questions:
(1) Do these valves go bad and if so how do you know?
(2) The button on the back of my valve doesn't seem to move at all when I press it. Do you actually feel it depress when you push on it? (maybe mine is stuck in the depressed position which is why its easy to bleed my front brakes)
(3) Should the button be easy to depress or is it pretty hard? (given its location, I'd hope it wouldn't be too hard or you'd never be able to push it in without unbolting the valve first)
(4) To bleed the front brakes do you press the button once or does it have to be held in the depressed position as the brakes are bled?

Thanks.
1 yes, they leak around the "stem" or push button under the rubber cover. There is an o ring inside.
2. 3. it should move inward and stay there, but pressure inside the line will push it back out, like stepping on the brake pedal.
4. you have to press it in and hold it. you have to clamp it in, you can't hold it with your fingers.
Once you develop more than 30 to 40 psi in the brake lines, the valve opens and allows fluid to go to the front brakes. That is enough pressure to overcome the rear brake shoe springs pressure so front and rear brakes start operating at the same time. Imagine a cold icy morning your auto choke is on high idle 2200 rpm's. you put the car in gear, auto transmission, your foot is on the brake but without the valve, light foot pressure will hold the front discs but the rear shoes will not be up against the drums. The rear wheels would spin if the car is on an icy street.
A pretty rare issue.
 

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Imagine a cold icy morning your auto choke is on high idle 2200 rpm's. you put the car in gear, auto transmission, your foot is on the brake but without the valve, light foot pressure will hold the front discs but the rear shoes will not be up against the drums. The rear wheels would spin if the car is on an icy street.
A pretty rare issue.
...which makes you wonder why manual trans cars got the valve....



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Discussion Starter #7
Thanks to you all for the feedback, it's a huge help. Answered all my questions and even provided a source for rebuild information and parts from a new source I'd never seen referenced - fantastic! That's what I love about this site, you learn something new every day. Guess I need to rebuild my valve which also means I'll need to bleed my brakes again - I hate that job. I still wonder why I've been able to bleed the front brakes using the Motive and only about 10 - 15 psi and not depress the valve. Maybe it's pitted inside and leaking past the seals. Oh well, just one of the joys of owning these cars.
 
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