How stiff are your brakes?
 

The brakes on my 240Z are fairly stiff. When I compare the stiffness to that of the brakes on any other vehicle I have driven, the Z takes the cake, hands down. The car stops when I need it to, it's just that the brakes are quite stiff. They have always been like this, ever since I had the car. When the car was given to me, my father and I replaced the brake booster, because the old one was not sealing and had a huge vacuum leak, and now I'm wondering if the newer brake booster we got from pick n pull may have the same problem. The car doesn't seem to have a problem with vacuum like it would if the line from the intake manifold balance tube was removed, but I am unsure if the brakes are supposed to be this stiff.

I think you answered your own question. Junkyard brake booster? Dude, that's just a bad idea. There are some things you just don't get from a junkyard and brake boosters or master cylinders are some of them. Not to beat you up over it though, I would say that your problem does indeed sound like a faulty booster. Get a new one or a remanufactured one next time around.

Rod.

but a bad booster would have a vacuum leak, correct.

Not neccassarily...

oh, see, that was the problem with the last one, so I assumed that was the way to tell. thanks for the info rod!

No Problem, 90% of the time a bad booster's only symptom is an extremely hard pedal. It depends on where the failure is though as to what else me be affected or what other symptoms it will demonstrate.

Rod.

If you drive at about 35 mph and turn off the key, the brakes should get harder each time you press on them. If it is just as hard every time then the booster is bad. Make sure you have room for this test. Another test is to pump the brakes with the engine off and car stopped. Then hold the brake pedal down all the way. Start the engine, the pedal should push against your foot.