1969 Camaro pressure regulator valve

[starrider]

i have a 247-8

[m22mike]

A little off track but this from the CRG may help with understanding usage on the pressure regulator valve.

Pressure reg valve

Valve Usage
Usage of the valve was not consistent.

•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.

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?