SUMMARY: THE REAR CYLINDER DIAMETER WAS REDUCED FOR 1984 MODELS TO IMPROVEBRAKING BALANCE FOR EMPTY VEHICLES.GM CLAIMS REAR BRAKES CAN BE LOCKEDON MOST EMPTY PICKUPS ON LOW TRACTION SURFACES.ANALYSIS:PICKUP TRUCKS TRADITIONALLY HAVE BEEN DESIGNED WITH BRAKINGSYSTEMS WHICH CAUSED THE REAR BRAKES TO LOCK FIRST WHEN THE CARGO BED ISEMPTY, SO THAT MAXIMUM EFFECTIVE BRAKING IS AVAILABLE WHEN A LOAD ISPRESENT. MOST MODERN LIGHT TRUCKS AND VANS UTILIZE WEIGHT SENSITIVE PROP-ORTIONING VALVES TO PROVIDE GOOD BRAKING AT ALL LOADS.STATUS:C-MEMO MAY NEED REVISION.IN FINAL BY 12/31/87.===