Id half agree; if the shoes were that far out the pedal would have been incredibly low before the emergency stop. I made the mistake of being lazy and bringing my car to a local shop to have the rear cylinders replaced; they gave the car back to me with a brake pedal that didn't work until it was 1/2 an inch off the floor; told me "some cars are just like that." I told them to tighten the shoes up and the tech says "well I have never tightened them THAT much". They also installed the adjusters on the wrong sides. Please. Anyway, I would also bet if the rear end wasn't ever serviced the cylinders could have just been old.

Second theory; On my old Sebring I had to do a quick stop on the highway that resulted in a brake line cracking that eventually let loose a week later. Pedal felt lower and lower and eventually stopped working. Point is, if its low, you have a loss of pressure SOMEWHERE. Master cylinder is one of those "complicated and scary" sounding parts that shops tell you they need 100's of dollars to replace. They are pretty simple on the HHR. Don't fret! Don't forget to bench bleed!

 

Did anybody even look at the rear brakes?

 

there was a moment when I did this.
the brakes worked fine, but according to my calculations, the brake pads should already be worn out.
Unfortunately, this can be verified only after disassembly.
So I bought a set of brake pads, and brake cylinders just in case not to come twice.
After removing the brake drums, it turned out that the brake pads were indeed already preparing for death, and the brake cylinders were in satisfactory condition. Nevertheless, I replaced both.

 

My ‘06 HHR works somewhat better after mechanic bled the lines a 2nd time. They said they fixed it but pedal still sinks after the initial burst of stopping power is applied. Pedal then drops about 2”inches. I don’t seem to remember it doing that before this all happened. I’ll pursuing this w brake specialists.

 

Good idea, perhaps they will actually fix the problem.

 

I'm not an expert.
Nonetheless, it seems to me that Satan has settled in the field of vacuum booster and master cylinder.
I will not recommend you replace it without checking - it is expensive. But a close look there will not hurt.

 

don't think that I want to be smartaleck ...
just a clarification useful to life ...
Water cannot be “more compressible”; water is not compressible at all under any circumstances.
The problem of water in the brake fluid is of a different nature. Water boils at 100C, which is critically small for brakes even with moderate braking. Water-saturated brake fluid, after two / three steps on the pedal, forms water vapor bubbles in the braking system. This effect is equal to not pumped brakes. Only hot vapor instead of air in the hoses.
Dear Blue_SS is right, as always, bat he was just a little informed.