Firebird Dash Brake Light

Chances are there is a leak in one of the lines. Pad and lining wear is not an issue. First of all, watch your parking brake light very closely with the engine not running. If it gets the very tiniest bit brighter when you apply the parking brake, that is not the reason it is on. Next, unplug the fluid level sensor in the master cylinder reservoir. If the light goes out, add more fluid or check if the float has sunk. Finally, unplug the pressure-differential switch in the combination valve. It's near the frame under the master cylinder. If that makes the light go off, the valve is stuck in some corrosion. It's spring-loaded in Chrysler and GM vehicles. A good jab on the brake pedal after the leak is repaired will usually unstick it.

If you have the "newer" master cylinder with four steel lines coming out of it, let me know as there are some important differences, but that system is usually used only on front-wheel-drive cars.

Caradiodoc

Sometimes that trick works to prove the light is NOT on because of the parking brake. When the brightness doesn't change, it's not conclusive. Before you tear into it more, look for an electrical connector on the master cylinder. Unplug that and check if the warning light turned off.

How many steel lines are there on the master cylinder, two or four? If there's only two, look for a valve assembly mounted to the frame below the master cylinder. That will also have a connector that can be unplugged to see if the light goes out.

Brake linings don't wear out that fast unless one cracks off from the metal backing plate. Also, the low fluid level switch is in the reservoir, not down where that plug is located. For the pedal to drop so quickly there is either a leak or there's internal leakage past a seal inside the master cylinder. That would cause unequal pressures in the two hydraulic systems. That's what that switch is for that you unplugged.

That block does look different than a typical combination valve but I couldn't tell if it was something related to anti-lock brakes. Normally if they used a scanner to retrieve fault codes the yellow warning light would have been on previously too. You'd have to ask if they used a pair of pressure gauges at the master cylinder or if they just based their diagnosis on the symptoms. If you see fluid residue by each steel line at the master cylinder, they likely used two gauges, but keep in mind they would have probably washed that off rather than leave a mess behind.