68 Brake issue. Input needed.

[David K]

I didn’t see where you mentioned what engine you’re have, and you mentioned low vacuum.

[Tinkerr]

Do you have the proportioning valve on the drivers side of the sub frame. I had a issue with mine, could get a little fluid to the rear, but no full flow. If you have the valve(and you should)crack the line on the down stream side of the valve to check for fluid, if no fluid then crack the up stream side to check for fluid. I could remove the down stream line and only get drips on mine.

[cwyllie]

David K. L34 396.
Tinker. That is exactly what I did while troubleshooting yesterday and was happy to see good flow on the backside of the distribution valve. I then removed the line at the right rear wheel and no flow at all. Now, I am in the process of changing the rear axle hose. The fitting on the front of the hose is seized. I hit it with heat, pb blaster and cannot get it to loosen. I am using a flare wrench and I can feel it is about to strip the nut. I am hoping that if I can get the hose replaced and blow out the rear lines to the wheels I may be in good shape.

[Sauron327]

Collapsed rear flex hose is common. When I do brakes on any of my cars I change them all. If you use heat, cut the line in half first, unless you got one end free. If not the heat will make the line pop and wake you up. It really helps others to use correct terminology when referring to brake components. http://www.camaros.org/brakevalve.shtml

[Tinkerr]

Are you referring to picture #1 distribution block under master cylinder or #2 proportioning valve on the side of sub frame.

[cwyllie]

i apologize for my misuse of terms. I replaced the MC, booster, distribution block and metering valve. Getting plenty of flow through the prop valve on the subframe. Replaced rear rubber hose today and getting good flow to all four corners.
took it out for a drive and again, same issue. Great pedal, and breaking for the first couple of miles. Then hard pedal, brake light and very little braking power.

[Tinkerr]

Have you been tried replicating the issue at home on jack stands. Make sure brakes are releasing and applying equally. Just grasping at straws.

[cwyllie]

Tinkerr.
Yes I have. After installing new MC and new distribution block, and rear flex hose.  I took the car out and once again I had good working brakes until the car was up to temp then it went to hell. Brake pedal feels like it hits a wall near the bottom, brake light comes on, and very little braking.
Next day I put it on stands to experiment. Started car and had good booster, good pedal, no light. Checked vacuum at 15in idle (cold). Pushed pedal about 30 times while warming up and everything was good. As soon as car was to temp, the problem came back. However when I pushed the pedal and hit the wall of resistance about halfway down and the light comes on, if I help pressure on the pedal it would drop another inch and light would go off. I could repeat this over and over.
Somehow there is a pressure issue in the system but cannot determine where the issue is.

[Tinkerr]

Again grasping here. Why does engine heat effect it? I think I’d replace the booster hose. Use a generic 3/8 hose for testing in driveway only, see if results change. I had my proportioning valve rebuilt the rebuilder  put the seals in upside down, cause a issue for me. So rebuilt isn’t always correct. Don’t know if it could cause your issue are calipers or the correct sides, bleeders up?

[cwyllie]

Booster, hose, and check valve have all been replaced. Calipers are correct sides.
Thinking maybe change out the pressure reg valve on sub frame. That is the only part that has not been replaced on the system.

[Sauron327]

Why not rebuild it?
Does anyone actually work on their own cars anymore from A to Z?

[cwyllie]

 Sauron327.
What do you think I am doing? Been chasing an issue and looking for answers so I can fix it.

[cwyllie]

ISSUE RESOLVED 
I replaced both wheel cylinder's at the recommendation of a very helpful CGR member. I also replaced the metering valve again just because it was suspect.
Today, upon completion and bleeding, I have brakes!
Personally, I think it was the wheel cylinders. They seemed to have more travel than the old ones and generally work better. Could probably put all my old parts back on and return the new ones... but I won't. Will try my hand at rebuilding some valves this winter when time allows. Overall, this was a great learning experience with my new car.
Thanks for all of the input from everyone.
Big shout out to my new Camaro buddy. 

Craig.