Air disc brakes.

What axle do you have that they wouldn't do discs? Late 2012's would even do it on airtek.

 

Meritors in back, Detroit in front. The claim was that the air discs required the newer wiring systems that the glider did not have. I thought it was all hooey, but nonetheless, I couldn't get air disc as an option on the glider. You have to keep in mind, that the Freightliner gliders are based on earlier versions of the models of trucks they are offering.

 

I think a salesperson was lacking. I'm sure the glider came with ABS,same sensor for disc or drum. Other than recording data to the trucks ecm the ABS module is the same on either.