Sales of Class 8 trucks in July fell 5 percent compared with a year ago. A total of 13,386 units were sold.
Sales leader Freightliner, owned by DaimlerChrysler AG, bucked the segment's downward trend, posting a 5.7 percent increase to 4,598 units.
Through the first seven months of this year, Freightliner's sales were up 6.1 percent to 45,293 units compared with the same period in 2002.
Sterling and Western Star, both also owned by DaimlerChrysler, were the other Class 8 makers to post increases.
Sterling's sales were up 35.4 percent to 1,024 units. Western Star's sales were up 11.1 percent, to 160 units.
Mack posted the segment's largest percentage decline for the month, down 34.6 percent to 1,212 units. International's sales were down 7.7 percent to 2,142 units for July.
For the first seven months of the year, International's sales totaled 12,238 units, down 6.2 percent.
Class 8 truck sales for the first seven months of the year, which totaled 76,321 units, fell 5.6 percent compared with a year ago.
Sales of Class 4, 5, 6 and 7 trucks all were up in July compared with July 2002.