I have a 1985 300zx N/A 2 seater 5 speed. Iv had the car for about 2 months now driving it around and everything was good. The other day I hit the brakes and the car barely slowed down, they still worked but just barely, pedal goes to floor.

So I carefully drove home to figure out the problem. I checked for leaks. Checked all brake lines and they are in great shape, checked calipers and hoses, also in great shape. Master cylinder and connections also no signs of leaks. So i assumed there was air in the lines and ill bleed the system the old fashion way with two ppl (pump then crack the bleeders). I looked in the reservoir and the fluid was pretty dark. Anyway we started to bleed and the two from bleeders for the first few bleeds was yellowish bubbly fuild, yuk. There was alot of air in the front 2 caliper brake lines. No matter how many times we attempted, it was mostly air and spitting a bit of fluid each time. The backs were mostly fluid no air.

However our problem is we cant get pressure to bleed the brakes! Pump pump pump and the fluid would just slowly drizzle out of the bleeders, on all 4 wheels. The master cylinder/brake booster make a really distinctive fluidy sound, very bubbly. We noticed that inside the back of the reservoir there were bubbles coming from the bottom. What is this and why isnt there no pressure?? When the car is off the pedal goes to the floor with a bit of pressure. When the car is on, the pedal goes to the floor very easily no pressure at all. Is the master cylinder dead? Any help would be appreciated.

Here are some videos of whats happening:
Cant get pressure in brakes! HELP!! - YouTube

 

Did you bleed the master cylinder?

 

Good call Nismopick. Wont get much out if air is in the main mastercylinder valve. You are doing one at a time with all others closed off? Build up as much pressure as you can before opening bleeder. make sure pedal is all the way down when you close it off. Do this 5 to 10 times in a row and you should have all of the air out and a nice pedal.

 

When we bled the brakes we did one at a time and pumped the brakes many times before cracking the bleeder screw.

No we didnt bleed the master cylinder because I thought, well if the brakes worked before and the fluid level never went down, how could air of gotten in the master? Is it possible for the master cylinder to be sucking air in but not leaking fluid out? Can i bleed the master while its still in the car?

 

Yes...

Brake bleeding 101: BLEED MASTER FIRST.

 

Ok so I unscrewed the 3 brake lines going into the master cylinder, topped off the brake fluid and started the bench bleed in the car. What I found is after most of what ever air was in there got out, only the front port closest to the front of the car (Ithink its the line going to the rear wheels) was shooting out brake fluid when the brakes were applied. The 2 other ports didnt even dribble out. So what im guessing is the seals in the Master for those two ports are shot and whats causing the problem? Would it be better to buy a rebuild kit or buy a new master?