It's not a hold off valve or a residual valve. It regulates rear brake pressure in proportion to front brake pressure... a proportioning valve. It reduces the rear pressure during hard stops to keep the rears from locking up. It was used on many cars with high front to rear weight differences, such as with big block or A/C.
Pontiac lists it as used "with disc brakes, with A/C" for their Firebird, but Camaro seems to me to be more arbitrary in their useage. The two cars used the same valve, same part number. The rear brakes were made small enough that many cars were expected not to need this valve. It basically does the same thing as the adjustable valves do, but it's not adjustable.
Here's some great info on this valve provided by our moderator, David Pozzi.
http://pozziracing.com/prop_valve_info.htm
Pontiac lists it as used "with disc brakes, with A/C" for their Firebird, but Camaro seems to me to be more arbitrary in their useage. The two cars used the same valve, same part number. The rear brakes were made small enough that many cars were expected not to need this valve. It basically does the same thing as the adjustable valves do, but it's not adjustable.
Here's some great info on this valve provided by our moderator, David Pozzi.
http://pozziracing.com/prop_valve_info.htm
