I've got an 85 with the 12A in it. My car had been sitting for 8 months and the brakes locked. I had someone else rebuild them and all was well. 4 Months later, one day my brakes suddenly felt not there. The car stops still, but there is no resistance in the brakes. I wouldn't call it a spongy feel, it's like the only resistance is that of the spring that returns the brake. The braking is also at a lower level. To lock the wheels, the pedal goes all the way to the firewall, before there was deffinately more gap. I looked in the brake reservoir, and the level was below minimum, and a bit black. I flushed the system and bled the brakes (possibly correctly, I couldn't find a bleeder on the left rear, am I stupid, or does the conection to the right rear let it bleed?) Finding a little leak on the front right. I was hoping this would fix my problem, no such luck. Now I didn't bleed the master cylinder, due to lack of time, and hearing it was a little more complex. Could it just be air in the master cylinder, or is it probably more complex and I should head out to find a competent mechanic.

 

Disc or drums on the rear? Does your parking brake act normal?

 

They are drums in the rear (I think it's a GL, all stock.) and the parking brake works fine. The parking brake light never shuts off but the brake isn't on, and when pulled it keeps it on the hill, so I don't think there's anything wrong there besides a short somewhere.

 

could be the master cylinder leaking on itself.

 

thats what i think too it might be your master cylinder or if you got power brakes could be your brake booster

 

definatly your master cylinder...the "spongy feel" is air being compressed. always bleed the master cyl then start at the right rear, then left rear then same up front right then left

 

It's also possible that the rear adjusters are not working. Air trapped in the master cyl is a good possibility, as well. You may be having more than one issue. Loose front wheel bearings can also cause a low brake pedal, as the rotors will wobble, pushing the pads further apart.
As for the left rear not having a bleeder, you are correct. On drum brakes, the entire rear system is bled from the right rear.
The "Brake" light is not just for the park brake, it also warns of low brake fluid level in the master cyl, and is turned on when the pedal travel goes too far. In other words, it's trying to tell you there is a problem in your brakes.

 

Bleed the entire system. Had a similar problem and had to bleed the master cylinder to rectify. Don't forget to do the rear brakes first then front right/ front left and make sure resevoir is always 3/4 full.

 

Frozen calipers? I reccomended doing the flush, too.

 

Again, master cylinder problem. A flush should fix it.