I'm not sure that is the right name for the rear brake line block that attaches to the subframe under the driver's door area. What were the applications that included these, and were there different blocks for different drive trains/convert or coupe/etc. One came with my 1969 convertible, but I do not know the whole history on the car. I do know that I'm putting in a 350 with Muncie 4 speed, 12 bolt 3.08 rear end. How can I tell if I have the right one, and do they age? Need to be rebuilt? :confused:

there were a couple different ones, but i think all the 67-69 camaro/firebird ones were the same. they were primarily on A/C,v8,disc cars, but there are exceptions. weight transfer is the key reason to use one in a stock application.

it reduces pressure to the rear brakes in proportion to the front, so yes it is a rear brake pressure regulator, or a proportioning valve.

it has a spring and a piston. i dont think there are any rebuild kits for them.

the spring controls the knee point, or, pressure at which it begins proportioning.
according to possible specs published on david's site (http://ourworld.compuserve.com/homepages/David_Pozzi/prop_valve_info.htm), anything above 230-270psi gets reduced, so it is only used during hard braking. if the spring gets weak, it will reduce pressure early.

the piston controls the slope of the reduction (i.e. a .45 slope would be 45psi output for every 100psi input over the knee point). i dont see how this could really go bad unless it could corrode or wear somehow, and let more pressure through.

i recently recommended someone with this valve keep using it but change the rear cylinders to the '76+ larger ones. she wanted to appear stock, and the valve is useful for slippery surfaces. the OE cylinders are way undersized IMO because they were designed to operate without a valve.
she says it stops great.

other options would be to gut it, run without one, use an adjustable, or use a combi valve. the 71-75 Fbody combi valve had no rear proportioning in it as far as I know. i would use the OE size cylinders if running without the valve.

here (http://pg.photos.yahoo.com/ph/pearlfootprints/detail?.dir=d9df&.dnm=f5b6.jpg&.src=ph) is a graph i made showing cylinder output with and without valve, and with a larger cylinder. it represents #force of one piston.
i also did not include that it has a maximum output of ~1038psi, but it shows a general view.

sorry if this is not the info you want.

Thanks so much for the information. My regulator block has been sitting disconnected from the lines for 15 years, so I was expecting it to be a bit dry and corroded inside. I'll start by filling it with brake fluid and submersing it in fluid in a sealed jar for a while.