My 78 was pulling to the right every time I applied the brakes, so I did the logical thing and replaced the left front calipar... good idea, but had no change in the pulling.

Next, I changed the proportioning valve with a new one from Eclklers.  When it came, it's shape was identical to the original one with the exception of an additional bolt-type head located in between the (what I think are the) lines to the front brakes.  Everything mounted up easy enough, and all brake bleed points were bled.

When I test drove it - no more pulling when the brakes are applied.... GREAT!  but oh, oh.... the pedal began going to the floor.  So I limped back to the garage.

Found new brake fluid leaking from that bolt head thingy in the front of the proportioning valve.   The original doesn't have this, and I have no idea how to proceed now... HELP???

Lockdown38913.5905671296

Sounds like it may be a bleeder hole for the valve itself.  You may need to fit a bleeder valve to it.  Does the hole have a small hole in the bottom with angled faces like you would see on a caliper's bleed hole?

The other thing it may be is a fitting hole for an indicator switch for the later cars which had different brake fault lights on the dash.  If you look in the hole and there is a shaft with a groove in it, I reckon that's what it may be.  So you may have to block it or fit a switch.

Chips5838913.7033680556

I think Chips is on the right track. The fitting on the front edge of the p-valve should have a switch installed, but not all cars had one, so the hole is plugged.
Take the "bolt head thingy" out, and look into the hole. If there is a flared seat at the bottom, you must use a flared plug to seal the hole. It's possible the bolt head thingy is just in there to keep dirt out, until the p-valve is installed.
Is there a chance you can get a pic of the hole, and the bolt head thingy?

I just love all the HIGH-TECH talk in hereDon't forget the  whatchamacallit,Doowacker,Thingamabob,Trundelbearing,Whogeew adjet Ron 7838914.32625

ok, I think I can get a pic of the left handed wrench thingy today (ie: the "bolt head thingy"... lol) and post it later.  I've already installed the p-valve on the car, but might just be able to remove the bolt thingy... we'll see....

I don't think it's a plug to keep the dirt out until the valve is installed.  All the other holes had rubber or plastic temporary caps on them.  This is more permanant.

Assuming it requires a "flare plug", where would I get one?

Here's a few pics of it installed.  These pictures are taken from above, as you look down under the master cylinder.

http://www.ifihavetoexplain.com/mis/ProportioningValve1.JPG

http://www.ifihavetoexplain.com/mis/ProportioningValve2.JPG

Lockdown38914.5252777778

Dave, that is the safety valve!!
It is designed to flop from center, to one end in the event of pressure loss on one end of the car. That valve is defective!!!
Sorry, but you're gonna have to take that one back and get a good one!!

Thanks Adam... I think..lol

I got that one from Ecklers about 2 weeks ago... hopfully they'll take it back w/out problems....

Yep, Ditto with Joel on that one.

Thanks guys, I am definately not the most brake savey dude on the planet so I read this with intrest. I didn't realize this valve existed but do now.
Thanks for the info! I now will know what I am looking at if I should run into this unwillingly.