I've been trying to figure out this problem with the brake pedal for a bit now, on my 87 Brat. It has a new master cylinder in it, but the pedal will go down rather far before I get good pressure. If I do a quick pump with the pedal, it will come back up towards the top. I've bled the system a few times myself, and recently had a brake shop do a flush on the system. They said they got some air out, and did it 3 times. But the problem didn't really change, though my parking brake does feel firmer now that it did before.

 

Is there still air in the line? Or is something else happening here?

Parking brake needs to be properly adjusted along with the rear brake adjustment.

 

Also, these are a X-plumbed system.

Bleed PS rear - DS front, DS rear - PS front.

 

Does sound as if there may be air in there still.

Tom pretty mach has this covered but I want to add that it sounds to me like improperly adjusted rear brakes. They arent self adjusting and must be adjusted with a spoon or screw driver from time to time. Its a bit of a hassle on these cars but I suggest a rear drum inspection. Those wheel cylinders seem to get leaky pretty quickly, most of the time they dont introduce air into the system but they could.

I will double check the rear adjusters. I didn't see any signs of leak from the wheel cylinders.

 

The shop insisted they got the air out, when I started pressing them about it because it was still feeling like air in the system to me. Then they started saying maybe brake booster and other things, but I didn't see how that made sense.

If the pedal is just low but firm and a pump or 2 brings it up... That sure sounds like rear adjustments. If the pedal is spongy with vague feeling stopping power then Ide say air.