Near the point of assembling my front subframe with original disc brakes. Have the booster/master cylinder with proportioning valve. What is the valve that is mounted on the frame for???

 

I take it you're referring to the block on the outer driver's side of the subframe? Chevy calls that a pressure regulator valve, other people like to refer to it asa proportioning valve. It controls hydraulic pressure to the rear brakes to keep the front to rear pressure balanced.
As the car came from the factory, the block below the master cylinder is abrake line distribution block/switch, not a proportioning valve. Are you sure what you're installing with your master cylinder is aproportioning valve, or is ita distribution block?

 

This is what this site says about it
http://www.camaros.org/index.shtml


Rear Brake Line Pressure Regulator Valve Usage
Although we continue to research the usage of this valve, this is a summary of what we know so far.
On certain Camaro models, a two-piece rear brake line with a brake pressure regulator valve was utilized. This valve mounts on the rear of the front subframe under the driver's door.



Rear Brake Line Pressure Regulator Valve


[/align]On the new 1967 Camaro, this valve was initially used only on models with factory C60 air conditioning and it was described in the 1967 Chassis Service Manual in the following way:


[blockquote]On Camaro models equipped with air conditioning, the rear brake hydraulic line is routed through a pressure regulator valve mounted on the left frame side rail (fig 3). The valve controls the hydraulic pressure to the rear brakes resulting in the correct pressure balance between the front and rear hydraulic systems. [/blockquote]
The November 1969 Chevrolet Service News adds the following (note that by 1970 the emphasis in the description was on front disc brakes, though the valve was also used on certain 67-69 drum brake cars):


[blockquote]The valve limits the amount of hydraulic pressure, at a controlled rate, to the rear wheels in proportion to the amount of pressure to the front wheels. ... This action prevents the rear brakes from locking up before the full effective braking effort is produced by the front disc brakes. [/blockquote]
The implicit rationalization in the 1967 description was that the valve was needed to improve stopping due to higher front end weight resulting from the C60 air conditioning equipment. Restricting use to C60 is suspect logic; there were other options that added the same (or greater) front end weight. For example, in 1967, an otherwise optionless L6 with C60 would get it, while a RS/SS350 with smog, power brakes, and power steering (but no C60) would not get the valve, despite having a higher front-end weight.
Valve Usage
Usage of the valve was not consistent.
[ul][*]1967 Camaros that received the valve were: all models with C60 air conditioning, all SS396 models, and NOR-built Z28's (at least the later ones). However, the 1967 LOS Z28's did not get the valve.[*]For 1968, only cars with 12-bolt axles received the valve. The C60 air conditioning option no longer caused use of the valve (though C60 cars could get the valve due to a 12-bolt axle). The one known exception is that NOR Z28's stopped using the valve midway through the 68 model and didn't begin again until mid-model year 1969.[*]For 69, the valve was generally used on 12-bolt axle applications, except for JL8 equipped cars (which had disc brakes in the rear and didn't need the valve). As noted above, the 69 NOR Z28's did not use it until mid-year, in the late January / early February timeframe. Other exceptions in 69 include: some SS's and LM1's have been observed without the valve, and the valve has been observed on some drum brake 10-bolt axle cars.[*]Note that usage of the valve on 67-69 Camaros was not apparently related to J52 disc brakes. [/ul]

Opinions differ on whether the valve was effective at reducing stopping distance, but CRG has not seen any comparison braking data. If it was effective, why wasn't it used on all models, and why was the Z28 usage irregular?




I have one on my 69 Firebird that came with A/C. front drum brakes

 

That is a cool bit of info...Thanks!

 

I wish I had my old school books. I remember them teaching us about the duel valve system. In later years the block was called a combination valve cause it housed both valves in one block. If I remember right the propotioning valve cause a slight delay so the back brakes come on right after the front brake and the regulator would keep the presure from getting to high and locking the back brakes to early. One of the 2 valve was not needed on a all drum brakes car. Sound like they where not sure when to use it and when not too.

 

My 69 Firebird has the Regulator Valve on the subframe and it came with all drum brakes. But had A/C

 

Great information.... I was speaking of the regulator valve. I have the complete proportioning valve/master/booster system ready to go. That other valve is the last item on the list. Thanks for all the input.