Correct locaton of proportionong valve on sub frame

[mrdetails]

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

[KurtS]

Picture emailed.

[JohnZ]

Here's the prop valve on my 02D '69 - still has the 37-year-old dealer-applied undercoating on it. 

[mrdetails]

Thanks so much.
Sam

[william]

That is not the prop valve.

[JohnZ]

That is not the prop valve.

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

[Mark's 68 L78 RS SS]

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

[RickH]

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.

[Mark's 68 L78 RS SS]

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

[mrdetails]

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.

[JohnZ]

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.

[william]

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".

[JohnZ]

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.

[169INDY]

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

[fireZ]

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.