I'm pretty sure ABS is enabled on rear-wheel drum brakes.
I can hear the front brakes hitting the ABS system (Which I don't and will never like), but since it's illegal to unplug or disable anti-lock brakes, I'll live with them.
But I never heard them engage on my rear wheels (drums)
I've only had the car for a couple of months, I have to do the rear brakes, so I could take a peek and come back to you.
On my Cavalier, the ABS would hit way too soon (caused me top rear-end a Protege), on the Contour, I would like them to engage a little later, but they're OK (been criving for the last 16 years.)
