In trying to work out the kinks of my rear 280zx disc swap, I decided to see if my reaction disk had fallen off in to the booster, indeed it had. I JB welded the reaction disk back the "plunger" and now my brakes have gone from mushy and then grabby at the end of the pedal throw to what I consider extremely firm with little pedal travel. The car brakes ok, but I feel if I had a little more pedal throw it would grab a lot better. I pulled the vacuum line between the check valve and the booster and the check valve was whistling, could that be bad? Now I don't know what to check next.

Did you adjust the push rod? The push rod clearance (or gap) between itself and the plunger should be around 0.3mm (+/- 0.2mm).

Here is a good how to: http://forums.hybridz.org/index.php/topic/102754-a-one-inch-diameter-brake-master-cylinder-for-the-s30-z-cars/

Is this where the threads are showing?

Did you adjust the push rod? The push rod clearance (or gap) between itself and the plunger should be around 0.3mm (+/- 0.2mm).

Here is a good how to: http://forums.hybridz.org/index.php/topic/102754-a-one-inch-diameter-brake-master-cylinder-for-the-s30-z-cars/

The 0.3mm is the amount of empty space that should be between the end of the pushrod and the black plunger in the master cylinder, I believe.

Ha, so the fact the I had to push the master cylinder against the pushrod and thus push in the MC piston means that bastard is way too far out?

Yep! If the push rod is sitting hard against the MC piston thats no good. You probably have to put a line on both of the side bleeders of your MC, routing them back into the reservoirs, to let out the pressure so the piston can release.

I adjusted it. It helped some but the pedal is still very stiff.

After getting past the required free-pay, my brake pedal is also very firm. The brakes are quite positive, though not "grabby". From my perspective, that's perfect.

The free play should not effect the pedal effort. Too much free play will cause a low pedal. Too little or no free play will cause the brakes to be held on all the time or when hot from driving. This will cause brake overheating, poor fuel mileage, and possibly wheel lock-up.

When the free play is set correctly you should be able to detect 2 distinct free plays. Pushing the brake pedal by hand you should feel the brake pedal touch the booster first and then the booster touch the master.

We had the same problem, high pedal effort. After an arduous trouble shooting process we determined the problem to be caused by badly overheated and glazed brake linings. New brake linings fixed the problem.