I was adjusting the length of the pushrod to match a new master cylinder and the threaded nose of the rod was very tight. As I attempted to turn it with a wrench, the whole pushrod would start to turn before the threads would loosen or tighten.

The first couple times it happened, it would turn a few degrees when a lot of force was applied, but now I can easily turn the whole pushrod by hand and it slides in and out freely. When pushing it back in, I can feel the end seating into a bore.

Is this booster toast?

edit: I am still able to pull vacuum on it with a little Mityvac hand pump.

 

I dismantled a ratty old FC booster I had lying around. It appears that the base of the pushrod isn't positively retained with any kind of seal or the like. Maybe the initial resistance to rotation I experienced was due to an old rust bond or ancient dried up grease.

 

In the above photos, the rubber 'reaction disc' (part #13) should be sitting at the bottom of the hole that the base of the pushrod sits in.


I had a brief moment of panic wondering if it fell out of place in the booster that I'd like to install in the car, but I can feel the pushrod bottoming out on rubber rather than metal-on-metal.