Medium- and heavy-duty truck sales rose 30.3% in Canada in July, the market’s fourth consecutive year-over-year gain.

The ascent was driven by increases in Classes 7 and 8, the only two groups in positive territory last month, compared with like-2009.

Related document: Ward’s Canada Truck Sales by Weight Class – July 2010

Class 7’s 74.3% jump was fueled by a 211.2% gain at volume-leader International Truck and Engine Corp. But Daimler AG’s Freightliner brand recorded the largest percentage increase, up 381.5%.

General Motors Co. suffered the segment’s steepest decline. Its sales plummeted 92.9%. Class 8 sales climbed 46.1% in July as Freightliner volume skyrocketed 172.7%. Daimler’s Western Star had the second-biggest jump, up 145.6%.

On the flipside, Volvo Truck North America Inc.’s namesake marque lost ground with a 22.3% shortfall. Daimler’s Sterling was shut out with zero sales vs. 88 year-ago.

Class 7’s sales increase offset declines at all other medium-duty groups and boosted the segment’s total 11% above like-2009.

Class 6 deliveries fell 33.1% on anemic sales by all manufacturers, notably volume-leading International, down 22.4%. Large percentage increases were posted on single-digit volume gains by Daimler brands.

Class 5 sales dipped 4.0%, with losses by some of last year’s biggest volume players, including GM, whose domestically built trucks suffered an 87% plunge. Daimler’s Sterling brand lost the most on a percentage basis, with sales down 94% on just one delivery.

Class 4 sales slumped 13.4% as more than half the segment’s manufacturers posted disappointing numbers. Volume-leader International provided the lone bright spot with a 15.6% increase.

Through July, Canadian big truck sales were tracking 14.1% ahead of like-2009.