I don't understand the bomb!

[Wallace White <whitew@leland.Stanford.EDU>]

I have received several replies (thanks) to say that yes, if the brake is
stiff after a few pumps, the bomb is dead. I also noticed that the brake
warning light came on about a minute after I shut the car off; I have
since read in the archives that this is another symptom. 

So, I'm still thinking about buying the car, but the bomb is bad. The
question is, what does the bomb do? Why does the car still brake well? And
does the bomb need to be replaced right away or once braking is affected?

Thanks, as always. I've found one more 5kcstq for sale with 110k, but it
sounds like it's had very few repairs as well. Rats.

- Wallace White
  looking for 5kcstq with lots of new parts