Hi guys, thanks for reading. I got a 78 280 and need advice as to what I should do to remedy a brake issue. I recently bought the car, and in the 60 or so miles i've been able to put on it, there has been an ocational loss in brake pressure when applying steady pressure on the peddle. it will sometimes drop to the ground!!! pressure returns after a few solid pumps but im worried that one day i wont have the time to pump!

I dont know enough to determine if its the booster or the master cylinder. We bled the brakes thoroughly in hopes that it was just air in the lines but it must be more than that because the problem persists.

Any help would be greatly appreciated. Thank you!

 

Is the brake fluid level going down at all?
Is the brake booster rusty?

 

Its definitely the master. A booster going out would be a hard pedal sometimes and soft others. Like Nismo said, check for rust on the booster where it meets the master. If there's rust there then the back seal is leaking and you'll need a booster soon. If not, then the seals inside are going out, and you should be able to change JUST the master.