What is this - Team Camaro Tech
Brakes, Suspension & Steering Conversion questions, Steering & Handling

 
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post #1 of 13 (permalink) Old Feb 24th, 09, 06:24 PM Thread Starter
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What is this

On a power disk brake car, there is little round thing that mounts to the booster. The line from it goes into the front tapped hole of the master cylinder. Have not seen this before. I will try to get a pic later.
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post #2 of 13 (permalink) Old Feb 24th, 09, 06:42 PM
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Re: What is this

This?

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post #3 of 13 (permalink) Old Feb 24th, 09, 07:00 PM
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Re: What is this

not sure? what is it? Poportioning valve?

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post #4 of 13 (permalink) Old Feb 24th, 09, 07:12 PM
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Re: What is this

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Originally Posted by 1SLOW64 View Post
not sure? what is it? Poportioning valve?
yes that's what it is!

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post #5 of 13 (permalink) Old Feb 24th, 09, 07:31 PM Thread Starter
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Re: What is this

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Originally Posted by SRGN View Post
This?
Yea, does that come on all Power disk brake cars?
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post #6 of 13 (permalink) Old Feb 24th, 09, 07:59 PM
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Re: What is this

Pretty sure that's the hold-off valve. Basically prevents fluid flow to the front brakes until some pressure threshold is reached. This lets the rear (drum) brakes take up the slack in the system and apply slightly before the fronts start to do any work. Net effect is (allegedly) a stabilizing effect (since the rear brakes will tend to straighten out the car when applied LIGHTLY) and reduced front brake pad wear (presumably by increasing the rear drum wear a bit and letting the rear brakes act a bit sooner).

At some point (1971?) GM rolled the prop valve, distribution block , hold-off valve, etc. all into a one-piece combo valve, but I think "everything" with front discs and rear drums in the 67-70 range had these.
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post #7 of 13 (permalink) Old Feb 24th, 09, 09:03 PM Thread Starter
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Re: What is this

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Originally Posted by TMessick View Post
Pretty sure that's the hold-off valve. Basically prevents fluid flow to the front brakes until some pressure threshold is reached. This lets the rear (drum) brakes take up the slack in the system and apply slightly before the fronts start to do any work. Net effect is (allegedly) a stabilizing effect (since the rear brakes will tend to straighten out the car when applied LIGHTLY) and reduced front brake pad wear (presumably by increasing the rear drum wear a bit and letting the rear brakes act a bit sooner).

At some point (1971?) GM rolled the prop valve, distribution block , hold-off valve, etc. all into a one-piece combo valve, but I think "everything" with front discs and rear drums in the 67-70 range had these.
Thanks, that is interesting and informative. This is the first disk brake first gen car I have had.
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post #8 of 13 (permalink) Old Feb 24th, 09, 09:54 PM
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Re: What is this

Yep, that's the hold-off/metering valve. The prop valve is the one down on the subframe under the driver's side door.

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post #9 of 13 (permalink) Old Mar 6th, 09, 01:10 PM Thread Starter
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Re: What is this

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post #10 of 13 (permalink) Old Mar 6th, 09, 03:33 PM
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Re: What is this

I hope JohnZ is lurking b/c this is the 1st time I've heard about a prop valve being mounted down by the lower frame??

I thought that was the 10 pound rear drum brake residual hold-off valve and if it isn't, I need to remove it so my new A/M adjustable prop valve works right for my "pdqCBB" setup.

I made sure that my rebuilt P/B M/C doesn't have any residual valves behind both line port seats so need to double-check this little ditty..........

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post #11 of 13 (permalink) Old Mar 6th, 09, 05:25 PM
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Re: What is this

Paul - you don't need the metering valve with 4 wheel disc brakes. Of course - in your case - it doesn't really matter on a car that sits in the garage and hasn't moved under its own power for what now - 10 years?


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post #12 of 13 (permalink) Old Mar 6th, 09, 06:05 PM
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Re: What is this

Quote:
Originally Posted by pdq67 View Post
I hope JohnZ is lurking b/c this is the 1st time I've heard about a prop valve being mounted down by the lower frame??

I thought that was the 10 pound rear drum brake residual hold-off valve and if it isn't, I need to remove it so my new A/M adjustable prop valve works right for my "pdqCBB" setup.

I made sure that my rebuilt P/B M/C doesn't have any residual valves behind both line port seats so need to double-check this little ditty..........

pdq67
4-wheel drum brake cars won't have a prop valve on the frame (no prop valve at all). I haven't seen a factory disc car, but the factory assy manual does show the valve located on the frame/subframe area under the driver's door opening....

And yeah, having 2 prop valves in series isn't recommended, so best bet is to remove it if you've got one...
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post #13 of 13 (permalink) Old Mar 7th, 09, 04:34 PM
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