Mystery

I finally replaced the brake master cylinder in the Volvo. I have a 740 that does not have ABS, but in ordering parts online, I found that some places don't distinguish. That's bad.

Sadly, I can't tell what was wrong with the old one. The fluid in the cylinder was full of fine metal filings (grey brake fluid instead of clear). The seals all looked fine and were not torn. By rights it should have worked. The only clue I was left with is the body of the piston has substantial wear marks. Perhaps 360,000 miles worth of stopping just caused the cylinder bore to widen enough that the seals didn't flare enough to seal against the sides.

Life is full of mysteries.

Regardless, the pedal is firm now, so I can approach traffic lights without a heightened fear of deploying the airbag.