Check Brake Drums (or Discs, Linings, and Hoses. Brake drums (or discs) must not have cracks longer than one half the width of the friction area. Linings (friction material) must not be loose or soaked with oil or grease. They must not be dangerously thin. Mechanical parts must be in place, not broken or missing. Check the air hoses connected to the brake chambers to make sure they aren't cut or worn due to rubbing. 5.3.3 – Step 7 Final Air Brake Check Do the following checks instead of the hydraulic brake check shown in Section 2, Step 7: Check Brake System.