Brake problems

[dvorak]

Hi everyone, I've just taken ownership of a '73 240Z and have started restoring it. I've run into one problem so far though. I can't get the brakes to fully work. I've changed out the rear wheel cylinders due to the old ones being leaky, and some new hard lines in to them. I pulled the MC and thoroughly cleaned it. I haven't done a full proper bench bleed, but I have used a vacuum bleeder on the the MC trying to get most of the air out. also used the vacuum bleeder on wheel bleeders and got the air out of the lines. However i'm still not getting any braking force. With the engine off the pedal is hard to push. when i start it the pedal goes to the floor with almost no resistance. I have to then pump the pedal to get any braking force.

[jhm]

Sounds like the master cylinder and/or slaves may need rebuild?  Did you replace the seals on the MC when you cleaned it?

[osirus9]

Is your brake booster to manifold line leaking air?

Edited April 22, 2014 by osirus9

[Pharaohabq]

Maybe it's the Reaction Disk had slipped out on it, Check it out on here with a search for reaction disk.

[NewZed]

I have to then pump the pedal to get any braking force.

The key to the majority of brake problems - if you can pump up the brake pressure there's air in the system.  Pumping compresses the air bubbles.  It may not be the only problem, but it's one that needs to be addressed.

[luseboy]

Ya definitely sounds like a bleed problem to me too.  I would say replace the master if this keeps up.  Also check and see if the reaction disk has fallen off.  Pretty easy to check if you're pulling the master anyways, though you'll likely have to pull the booster too if it has come off.  Check the condition of all your lines (hard lines and rubber lines) and make sure none of them are kinked, leaking, cracked, etc. as that could allow more air in the system.  First place to start is by bench bleeding the master and then re-bleeding the whole system.  

[Malarkey]

From what you've described, You have enough experience bleeding brakes to know if you've bled them enough and something else is the issue here. The next thing I'd check is that reaction disk mentioned in earlier posts. It more than likely fell inside the booster when you took your MC off.

Without it you aren't pushing the piston in the master cylinder very far in when you step on the brake.

[dvorak]

Sorry for taking so long, with work I really don't get much time to work on the Z, but here's some updates.

I replaced the MC with a new one that came with the car. I properly bench bled it.

Properly bled each brake line with someone pressing the pedal. I would have them hold the pedal down, open the bleeder, close the bleeder, let off the pedal, repeat.

I've found out that the block with the "Brake Line Pressure Differential Warning Light Switch" is leaking, but only when force is applied to the brakes. seems like it's leaking from one of the two ports on the bottom where the MC connects. 

When I start the car, the brake pedal goes straight to the floor, but if I pump it, it builds pressure and gets firmer. If I let it run for a a couple seconds after that all pressure is lost and the pedal goes straight to the floor.

Also found a plug unplugged and the "brake warning" light on the dash now comes on when I press the brakes and the pedal goes to the floor. When I pump them and the pedal gets stiffer, the light doesn't come on.

[Jaevee]

My guess would have been you had the lines wrong. Front to rear and rear to front. I bought a car like that least year and had to swap em and now the brakign is excellent.