When I drove the car yesterday, I noticed that the brake pedal goes all the way to the floorboards when I'm sitting at a stop light. The brakes work fine, stop the car, and they'll lock up if I want them to. But at stop lights, the pedal feels like its all the way to the floor. But again, it stops fine, and at lights, it doesn't feel like its going to move, its just feels strange to me.

All new brakes, everything bled properly, no air in the lines.

I don't know if this has something to do with the vacuum assist? This is my first Datsun, and maybe its normal, but it does feel a little strange.

Do you still have the drums in the back? Usually a low pedal means the drum shoes need to be adjusted up a bit. Does your handbrake come all the way up? If you know how to adjust them, adjust them up until they just start to drag as you spin the rear wheels by hand when its jacked up.

Just to clarify, is the pedal always low or does it gradually go to the floor while you're stopped? If that's how it happens you still have air in the lines or a minor leak at one of the cylinders, wheel or master.

I had the same problem, and it was a faulty master cylinder. After I changed it, the brake pedal didn't go nearly as far down. The car, just like yours, had no problem stopping, and I could get the wheels to lock as well, it just didn't feel right. It had to touch the floor before the brakes engaged with any significant power. Changed the master cylinder and it works fine. This is only one opinion though. Brakes are the most important thing on a car, so it would be good to check out all of the advice on this thread.

If the pedal slowly drops while you hold steady pressure on it, you either have a small fluid leak, or the master cylinder is "by-passing" - in other words, one of the seals inside the master cylinder is allowing the fluid pressure to leak back past the piston.

Often, a by-passing master will feel fine with a hard, sharp application, but will fall to the floor with a soft, steady pressure.

If you have a leak, you should have noticed a serious loss of fluid by now. If that hasn't happened, it's time for a replacement master cylinder.

I lost my master cylinder when I went out for a drive. I was accelerating and some idiot in an SUV cut me off. Slammed on the brakes and almost nothing. I had to lock the rears with the e-brake to slow down enough. the ride home wasn't fun.

luckily it only took me about a half hour to replace the master cylinder.

definitely sounds like your problem