Sales of medium- and heavy-duty trucks fell 32.1% in the U.S. in March, Ward’s data show, but still showed improvement over February, when sales slid 39%.

Class 8 halved its February plunge of 36.5% with deliveries down 17.9% last month, as a 3.2% increase at Daimler AG’s Freightliner brand helped to balance out losses at all other manufacturers.

Related document: Ward’s U.S. Truck Sales by Weight Class – March 2009

Volvo Truck North America Inc.’s Mack brand suffered the biggest loss in March among Class 8 vehicles, tumbling 53.8%, Ward’s data show.

Sales of medium-duty trucks dropped 41.0% last month, with Class 4, 5 and 6 plunging 40% or more.

Class 7 was the most resilient of all truck groups in March, off 15.8%, with Daimler’s Sterling brand, International Truck and Engine Corp., Isuzu Motors Ltd., Nissan Diesel Corp. and PACCAR Inc.’s Peterbilt brand all posting increases. However,

International was the only truck maker to sell more than 1,000 units.

Daimler’s Mitsubishi Fuso brand posted the biggest drop in Class 7 in March, down 48% on just three units sold, compared with six year-ago.

Class 6 saw the largest decline of all big-truck groups last month, with sales tumbling 56.4%. Only Isuzu posted a sales increase in the sector, up 46.4%, while nearly all remaining manufacturers saw declines of 50% or more.

Ford Motor Co.’s 82.8% plunge was Class 7’s largest decline in March, with Mitsubishi Fuso’s 81.6% loss not far behind.

Class 5 deliveries slid 42.0%, somewhat boosted by Sterling’s 56% increase in domestically built units. Peterbilt suffered the greatest falloff, plummeting 78.3%.

Class 4’s 48.9% drop was the second-largest segment decline in big-truck sales in March. Daimler’s Freightliner brand saw the biggest increase, up 52.2%, while its Sterling brand jumped 48.6% on domestically built units and 25.7% on imported models.

But the gains weren’t enough to offset a 71.2% plunge in Daimler’s Mitsubishi Fuso deliveries, marking a total decline in Daimler truck sales of 9.9%. However, International posted the largest decline in Class 4, down 87.5%.

First-quarter sales of big trucks in the U.S. trailed year-ago 37.3% at 47,698 units vs. 76,099. March sales translated into a seasonally adjusted annual rate of 200,000 units, down from prior-year’s 310,000.

Heavy-duty truck inventory at the end of March fell from 82 days, or 32,819 units year-ago, to 77 days, or 25,311 vehicles. Medium-duty trucks saw days’ supply increase to 97 from 85 year-ago. However, inventory fell from 54,461 units in like-2008 to 36,607.