Brake Pedal Hard- Cant figure it out

[kutukutu1]

All,

I have a 78 280z. The car has the 280zx rear disc conversion. The rear lines had been damaged and leaking.

I bought lines, swapped them and bleed all 4 corners and as well as bleed the master cylinder thru the bleeders on it.

The pedal is hard as a rock, cant lock the brakes and it takes a lot of pressure to slow down

Checked brake booster, it holds vacuum and the pedal felt softer when i drew vacuum so that rules out the booster.

I checked vacuum at engine at idle and its riding around 14 to 12 inhg which is low.

I checked compression and i get around 145 to 150 psi on the third pump on all cylinders so compression is good.

If i pump the pedal then hold and start the car, the pedal does not move further down.

I increased the idle rpm and the gauge reading went to about 15 inhg, but still the pedal was hard.

I am lost as to what else to do or check, any help is appreciated.

Thanks

 

[Diseazd]

Sounds exactly what you get when the reaction disc falls of of the Mastervac plunger. Did you remove the brake Master cylinder? If so did you pull the plunger out of the Mastervac? If so, the little round rubber disc that fits on the back of the plunger probably fell off. If you didn't do these steps, I'm at a loss for what it might be.

[kutukutu1]

Master cylinder and booster were not removed. Should i check that? I have never seen the car with brakes so the previous owner could have removed it and not done it right. Any steps on how to make sure that rubber disc is installed properly?

[Diseazd]

I'd bet on that being the problem. I had the same problem once....when I removed the plunger on the Master Vac, the reaction disc fell off. It two feet on the brake pedal (felt hard as heck) to stop the car....frightening!!!! Unbolt the brake Master cylinder ( you don't have to disconnect brake lines) and pull it back away from the Master Vac. Pull the plunger out....if there isn't a rubber disc on the end, you've got a problem. You'll have to vacuum out the disc (about the size of a half dollar and 1/2 inch thick. Super glue it back to the end of the plunger and push back in the Master Vac. Bolt up the master cylinder and you'll be frickin amazed at what a difference that little disc makes. Good Luck!

[kutukutu1]

Thanks for the help. Going thru the FSM, the little lightbulb in my brain stopped flickering and lit up. So i decided to check the check valve. I had checked it and i saw it was functioning, but didnt dawn on me that it could have been backwards. It was backwards. Have to love figuring out DIY work from previous owners. Now it brakes. Thanks you very much for the help

[Diseazd]

Awesome....good job!