sinking pedal syndrom

[dabby dunkerton]

hey guys i need some help diagnosing my pedal going to the floor i have 1977 280z and the brakes only catch on like the last half inch of the pedal then they sink to the floor.

 

Ive noticed when i get in my car the pedal is hard but can still be pushed to the floor but once the car is on it straight away gos to the last half inch without any pressure

 

the resivor is filled between min and max so im not missing brake fluid.

 

I searched the brake forums but to no avail and i dont wanna replace the master cylnder and have it end up being the brake booster so if someone could point me in the right direction id really appreciate it thanks in advance ill go out and take some pics of my new z once i get er running right!

[]2eDeYe]

Have you bled the system of all air? The reservoir full does not mean the there is not air in the system.  

 

If you have bled out the entire system, does this happens after you have come to a stop? If it happens after you come to a stop it is likely the booster. You can disconnect the vacuum to the booster and plug the engine side of line and see if the symptoms change. This will tell you if the booster is working correctly or not. 

[dabby dunkerton]

Have you bled the system of all air? The reservoir full does not mean the there is not air in the system.  

 

If you have bled out the entire system, does this happens after you have come to a stop? If it happens after you come to a stop it is likely the booster. You can disconnect the vacuum to the booster and plug the engine side of line and see if the symptoms change. This will tell you if the booster is working correctly or not. 

i have not i just picked up the car yesterday and i just wanted to be sure before i started working on something thats not the problem, I will bled the system and report back thank you so much!

[datzenmike]

Adjust your rear drums. If the shoes have to travel too far to contact the drums this will eat up pedal travel. (likely this is the problem)

 

If you have never changed the brake fluid now is the time. Keep the master full and bleed out all the old discolored fluid while bleeding the system.

 

 

 

Here's what to expect when you have power boosted brakes. Pump brakes several tomes to remove all traces of stored vacuum in the booster. Step down on brake and hold. Start engine. Pedal should drop slightly as manifold vacuum builds. This would indicate that the booster is working properly.