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Author Topic: Correct locaton of proportionong valve on sub frame  (Read 9054 times)
mrdetails
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« on: October 01, 2006, 08:49:12 PM »

Hello: I was trying to install the proportioning valve back on the sub frame tonight, but it seems the front stainless steel line is to short. The assembly manual shows the valve mounting close to the end of the sub frame. The holes fro mounting are their but the front line won't reach. Has anyone else had this problem? The car is 01D, might that make a difference or are all cars the same? I would appreciate any help. Always something.....
Thks.:
Sam
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KurtS
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« Reply #1 on: October 02, 2006, 01:41:31 AM »

Picture emailed. Smiley
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Kurt S
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JohnZ
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« Reply #2 on: October 02, 2006, 10:19:57 AM »

Here's the prop valve on my 02D '69 - still has the 37-year-old dealer-applied undercoating on it.  Smiley
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'69 Z/28
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mrdetails
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« Reply #3 on: October 02, 2006, 11:18:16 AM »

Thanks so much.
Sam
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william
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« Reply #4 on: October 02, 2006, 12:03:32 PM »

That is not the prop valve.
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JohnZ
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« Reply #5 on: October 03, 2006, 02:35:01 PM »

That is not the prop valve.

Why do you say it's not the proportioning valve?
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'69 Z/28
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Mark's 68 L78 RS SS
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« Reply #6 on: October 03, 2006, 05:30:48 PM »

My proportioning valve is just about exactly 6" on center in front of the bak end of the sub frame when measured from the top of the end of the subframe.

Mark
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Mark
Skaneateles, NY
68 L78 RS SS M22
RickH
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« Reply #7 on: October 03, 2006, 05:59:09 PM »

That is not the prop valve.

Why do you say it's not the proportioning valve?

I bet he's thinking distribution valve. Different animal.

Rick H.
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Mark's 68 L78 RS SS
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« Reply #8 on: October 03, 2006, 06:20:11 PM »

Here is a pic from my 68 L78 RS SS.  As I said it is about 6" from the back of the sub frame.

Mark
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Mark
Skaneateles, NY
68 L78 RS SS M22
mrdetails
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« Reply #9 on: October 04, 2006, 07:48:36 AM »

I disasembled this part for rebuild. It contains a valve seat, 2 seals, a poppet valve stem and a spring. This configuration of parts will allow fluid (or air) to pass only when a certain presure (that of the spring) is exceded. Call it what ever you like....  I appreciate all the help and photo's.
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JohnZ
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« Reply #10 on: October 04, 2006, 11:21:00 AM »

It's a proportioning valve that progressively limits pressure to the rear drum brakes based on line pressure at the inlet; the round valve under the master cylinder is a metering valve (or "hold-off" valve), which doesn't allow fluid pressure to the front discs until there's 30-40 psi in the line. The distribution block has no valving in it at all - it only activates its internal differential pressure warning switch (which lights the warning lamp in the cluster) when it senses a pressure differential between the front and rear systems.
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william
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« Reply #11 on: October 06, 2006, 06:59:57 PM »

I did not consider it the prop valve because the explanation in the November 1969 Chevrolet Service News refers to it as a "pressure regulating valve" 5 times in the short article.

Not all disc/drum Camaros had it; some drum brake cars have it.

What I consider the prop valve is the one under the master, Chevy calls it a "pressure metering valve" and also a "pressure regulating valve", point being disc/drum cars have to have it.

I checked the Assembly and Chassis Service Manuals-no mention of "proportioning valve".
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JohnZ
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« Reply #12 on: October 07, 2006, 11:56:09 AM »

I can't explain why Chevy named them the way they did, but functionally, the one on the frame is a true proportioning valve (and its function was later incorporated into the "combination valve" that combined proportioning, front metering, distribution, and differential pressure switch functions in the mid-70's). The round one under the master cylinder has no proportioning function - it just remains closed until its inlet sees 30-40 psi, then it opens and allows fluid pressure to the front discs.

The function of the round metering valve (or "hold-off" valve) is to allow the rear system to see 30-40 psi (which moves the rear drum shoes out into contact with the drums) before the front discs see any pressure, to avoid disconcerting "front brakes first" on pedal application, which causes "nose-dive" at low speed. The metering valve on my '69 Z/28 is stuck open (needs a rebuild), and at low speed light brake application the car nose-dives and feels like it'll stand straight up on its nose when you step on the brakes. Gotta rebuild it this winter if I can find the correct kit with ALL the seals.
« Last Edit: October 07, 2006, 12:02:12 PM by JohnZ » Logged

'69 Z/28
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169INDY
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« Reply #13 on: June 06, 2008, 12:39:33 AM »

Does anyone know of a source for the soft goods for owner rebuild of the subframe mounted:
"pressure regulating valve" or "proportioning valve" by whatever name,,,
1968 disc brake car w/ drivers side subframe mounted in-line pressure <do-hickey>

I have unmounted mine and removed the hex head cap screw and 1 rubber "V"-grooved cup seal and washer, to the point of a external snap ring and am not sure what lies beneath,,,,Lots of 'gunk' so I was interested in further disassy and cleaning, just was checking if others have dug into this component and sources for the soft goods needed to PROPERLY rebuild it, otherwise its just a careful cleaning and reassembly,,,

Thanks,

Jim
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Jim
68 SS/RS L35 Th-400 LOS
69 Pace Car L48 Th-350 LOS
fireZ
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« Reply #14 on: June 06, 2008, 08:50:35 AM »

I removed the one on my 68 Z and disassembled it. I cleaned and flushed it with brake cleaner and put it back on the sub-frame. Seems to work fine now.
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melav8r
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« Reply #15 on: June 09, 2008, 08:21:28 AM »

I can't explain why Chevy named them the way they did, but functionally, the one on the frame is a true proportioning valve (and its function was later incorporated into the "combination valve" that combined proportioning, front metering, distribution, and differential pressure switch functions in the mid-70's). The round one under the master cylinder has no proportioning function - it just remains closed until its inlet sees 30-40 psi, then it opens and allows fluid pressure to the front discs.

The function of the round metering valve (or "hold-off" valve) is to allow the rear system to see 30-40 psi (which moves the rear drum shoes out into contact with the drums) before the front discs see any pressure, to avoid disconcerting "front brakes first" on pedal application, which causes "nose-dive" at low speed. The metering valve on my '69 Z/28 is stuck open (needs a rebuild), and at low speed light brake application the car nose-dives and feels like it'll stand straight up on its nose when you step on the brakes. Gotta rebuild it this winter if I can find the correct kit with ALL the seals.

With that said I think my hold off valve (round valve) may not be opening soon enough since I tend to get premature rear brake lock up during panic stops. Because of this I took apart the subframe mounted proportioning valve and cleaned out what appeared to be hardened or glazed brake fluid gunk but the back wheels still tend to lock up during hard braking. Do you think tearing into the hold off valve will resolve my issue? how do you test the hold off valve for proper function?
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L78 steve
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« Reply #16 on: June 09, 2008, 12:38:21 PM »

As far as a supplier for the frame valve parts I had no luck at finding one .So I purchased a new re-pop from Inline tube and stole the parts out of it to rebuild mine .A little expensive but it worked .I got to keep my correctly dated valve .
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69 Z/28 Dover White X33,ZL2,PS,M20,Std.int.04C
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Buddy
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« Reply #17 on: June 10, 2008, 01:12:44 PM »

Quote
The function of the round metering valve (or "hold-off" valve) is to allow the rear system to see 30-40 psi (which moves the rear drum shoes out into contact with the drums) before the front discs see any pressure, to avoid disconcerting "front brakes first" on pedal application, which causes "nose-dive" at low speed.

Hey, thanx JohnZ, you just fixed my 66 Caprice 396...Woo Hoo  Smiley
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169INDY
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« Reply #18 on: June 15, 2008, 01:23:09 AM »

Here is an disassy view of the valve from the subframe:

Jim
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Jim
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69 Pace Car L48 Th-350 LOS
no69x-44
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« Reply #19 on: August 14, 2008, 02:57:59 PM »

Ok, this is not rockets science we are dealing with here ... But I have been having nothing but problems with my brakes now that I'm near the end of my rebuild. I don't want to bore you all with all the details of my woes ... But will just start off where I am now.

What I have is all brand new or newly rebuilt as follows:

Master Cylinder (309)
Proportioning valve
Disc Calipers
Pads
All Lines and Hoses
Power Booster
Etc.

So basically the entire brake system is all spanking new. There are no leaks at all and the brakes - front and rear bleed with a smooth clear stream (over and over again) and looks fine - no air. When the brake pedal is hit, the rear brakes work perfectly. No issues. They grab tight and hold.

Now the %^&#&% Front disc is another issue! They don't seem to grab at all. But yet, if I pump the brake pedal 5 or 6 times, the grab a little more with each pump, and then hold tight. Once I let off the brake, the it's the same thing again. 5-6 pumps before the front hold tight. Again the rear are working as designed.

I'm stumped and at wit's end on this. This should be a pretty simple thing and it is beating the crap out of me. I'm about ready to swap out the Master ... Again!

But after reading through this thread (good stuff), I am now thinking this just might a proportioning valve issue - even though I all ready replaced my original one (the round one under the master cylinder).  Any and all help/advice would be most appreciated.
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--Rob
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Sauron327
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« Reply #20 on: August 14, 2008, 03:58:29 PM »

 This should be in the Maintenance section. But if the piston is not returning in the master it will not function properly. And the round metering valve still may be at fault.   Once again-- new does not mean good.
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Sauron327
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« Reply #21 on: August 14, 2008, 04:07:50 PM »

 You may also have a check valve proplem with the master.

http://www.camaros.org/forum/index.php?action=search2
 
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firstgenaddict
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« Reply #22 on: August 15, 2008, 02:23:17 PM »

The 69 Chassis service manual says that the valve was only used on Camaro's with the 8-7/8 ring gear and only after mid year...
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James
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Check out the Black 69 RS/Z28 45k mile Survivor and the Lemans Blue 69 Z 10D frame off...
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169INDY
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« Reply #23 on: December 06, 2008, 05:16:16 PM »

Update w/ Disassy photos.

I ended up just taking it apart and cleaning it up w/ brake fluid and carfully re-assembling.


Hope this is helpful.

Jim
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Jim
68 SS/RS L35 Th-400 LOS
69 Pace Car L48 Th-350 LOS
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« Reply #24 on: December 07, 2008, 01:09:56 PM »

Ok, this is not rockets science we are dealing with here ... But I have been having nothing but problems with my brakes now that I'm near the end of my rebuild. I don't want to bore you all with all the details of my woes ... But will just start off where I am now.

What I have is all brand new or newly rebuilt as follows:

Master Cylinder (309)
Proportioning valve
Disc Calipers
Pads
All Lines and Hoses
Power Booster
Etc.

So basically the entire brake system is all spanking new. There are no leaks at all and the brakes - front and rear bleed with a smooth clear stream (over and over again) and looks fine - no air. When the brake pedal is hit, the rear brakes work perfectly. No issues. They grab tight and hold.

Now the %^&#&% Front disc is another issue! They don't seem to grab at all. But yet, if I pump the brake pedal 5 or 6 times, the grab a little more with each pump, and then hold tight. Once I let off the brake, the it's the same thing again. 5-6 pumps before the front hold tight. Again the rear are working as designed.

I'm stumped and at wit's end on this. This should be a pretty simple thing and it is beating the crap out of me. I'm about ready to swap out the Master ... Again!

But after reading through this thread (good stuff), I am now thinking this just might a proportioning valve issue - even though I all ready replaced my original one (the round one under the master cylinder).  Any and all help/advice would be most appreciated.

Compare old master cylinder with new, Check the depth of the hole of the master cylinder piston that the pedal pushrod fits into. Theres a chance that the piston is not being forced in far enough. I ran into this problem helping Ken Boje with the Gibb z/28
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tom
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« Reply #25 on: December 07, 2008, 08:34:37 PM »

Are the calipers installed corectly? I recall reading that they will install on the wrong side, but if that is done they do not bleed correctly because of the position of the bleeder leaves air in the caliper.
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