TM 10-3930-659-34 4-51. SERVICE BRAKE DISC REPLACEMENT (Con’t). 6. Remove three pressure plates (11) from differential case (7). 7. Remove three paper washers (9) and preformed packings (8) from differential case (7).  Discard preformed packings and paper washers. 8. If damaged, remove three pistons (10) from pressure plates (11). b. CLEANING AND INSPECTION 1. Clean parts with a clean rag. NOTE If   one   service   brake   disc   is   defective, both     service     brake     discs     MUST     be replaced on axle assembly. 2. Using dial indicator, measure service brake disc (1) flatness variation.  Flatness variation must not be more than 0.045 in.  (1.143 mm). 4-189