93 300ZX TT Sinking (to floor) Brake Pedal Issue

[VoodooTTZ]

I have a 1993 TT Z that is in good condition. I have recently replaced the Brake Master Cylinder, Clutch Master Cylinder, and Clutch Slave Cylinder. For some time (I can't remember if it happened before the replacement of above items or not ) every now and then, when I hit the brakes, the pedal drops to the floor, but when I'd react and let them up and hit them again (usually faster so as not to hit whatever I was stopping for) they work fine.

Well, I just discovered that I can replicate this at will now. If I very slowly depress the brakes with a constant pressure (as if trying to stop slowly while coasting slowly to a stop) the pedal will go right to the floor no brakes. As long as you keep pumping very slowly, you will never get brakes. Depress the brakes "normally" or "hard" and you get brakes every time.

Also, I followed the service manual explicitly concerning the brake bleeding procedure, I will likely try to bleed it once again, but I've bled it 3 times now, with no air bubbles. Again, when you brake normally, the brakes work well. Only if you "feather" the brakes will you run into the sinking pedal.

Any help or suggestions would be greatly appreciated!

Thank you!

[Ever Victorious]

How are you bleeding the brakes, manually or with a power bleeder?

If you're doing it manually, it still might not be bleeding correctly, there may be an air bubble simply stuck in the system (my last Subaru did this). Power bleeding fixed it.

If you've power bled it, I don't know the answer... but my first guess would be one or more bad calipers, or if this is a vac-assisted brake system (I'm not that familiar with Nissans), you might have a slight vacuum leak.

[Q45tech]

Master cylinder and system needs bleeding. Was master cylinder oem or a rebuild?

[nsrZ32]

Try using a power/air bleeder. Z32 brakes aren't the easiest to bleed. Its not super common, but I've seen others have problems with a soft pedal. Also, as I'm sure you know, the reason its soft is because air is compressable so the pedal sinks to the floor where as fluid is not so when properly bled and sealed, you have a firm pedal.