SUMMARY: RECENT ROCKWELL REPORTS IDENTIFIED THE FOLLOWING ADDITIONAL CONCERNS: A: INSUFFICIENT AIR PRESSURE DUE TO INADEQUATE AIR COMPRESSORCAPACITY; B: AIR HORN PLUMBED INTO AIR SYSTEM WITHOUT PRESSURE PROTECTIONVALVE; C: BRAKE IMBALANCE CAUSED BY BRAKE PROPORTIONING VALVES WHICHREDUCE THE FRONT BRAKE PRESSURE. THE ABOVE PROBLEMS MAY RESULT IN HEAT CHECKING AND CRACKING OF THE REAR BRAKE DRUMS.