Brake Pedal "Clunk" with 1 inch of travel

In early May my 1970 GS with the factory power brakes made a clunk when I pressed the brake pedal. I didn't think much of it because they still worked fine. After stopping for ice cream, my wife noticed the brake lights were on. The switch had popped out of the steel clip that holds it into the bracket. I replaced that switch with a new one and then drove 800 miles to Bowling Green and back without any stopping issues, but the pedal seems to have two "resting" heights. I can pull the pedal up with my toe or hand and it will clunk and stay. I can step on the pedal and it will clunk and stay 1" lower. The same condition exists with the engine running or not. This makes adjusting the brake light switch difficult.
Almost all of the brake components were new or restored in 2011-2012. So other than one leaky wheel cylinder, the system has been functioning for 10 years and 10,000-plus miles. The yoke that connects the booster to the pedal is tight, so I think this pedal travel is on the other side of the firewall. I use a Master Lock club to lock the brake pedal to the steering wheel when I store this car. Installing this lock pulls the pedal up.
Does the spring in the booster ever break? Does the pin between the booster and master cylinder break? Does everyone have a pedal that pulls up 1"?

 

Your going to have to take a looky see under the dash

 

Generally, thats a sign the booster is on it's way out. You might find that it's releasing the brakes slowly as well, watch your brake lights to see if they stay on after you release the pedal.

 

Nothing obvious under the dash. I was hoping something simple had come loose.

 

I'm going to pull the master cylinder off and check the spring inside the bore. I've never seen one of these broken before, but I guess that's possible. After that I'll focus on the booster. There aren't enough threads on the brake light switch to use the lower resting pedal height as the "off" position on the switch, plus I really don't want a brake failure.

 

I removed the master cylinder from the booster and the springs inside each of these seem to be just fine. The left/outside stud that the master cylinder bolts to was missing about 1/2" of threads.

 

THAT could be an issue