There are no wires or anything going to my rear brake unit, so I'm not sure they were ever anti-lock.
And even anti-lock will fail safe to conventional. My 2004 Silverado anti-locks failed, and I unplugged them. They continue to work in normal mode.
The anti-lock part of the system is more part of the master cylinder, or at least installed close to it. All that is installed on the axle are the speed sensors.
