Heavy- and medium-duty trucks finished 2012 with U.S. sales up 13%, despite a 0.5% December dip.

Big truck makers sold 345,876 units in the year, marking the best results in five years, WardsAuto data shows. Deliveries hit 371,093 in 2007.

Daimler retained its position as the volume and market-share leader in Class 8 for December and for the year, with share climbing to 34.2% in 2012 from 31.7% in 2011.

International’s Class 8 sales slid 27.1% in December and were down 3.1% for full-2012. The truck maker continues to struggle from fallout over a decision to clean diesel-engine emissions with exhaust-gas recirculation technology, compared with the more common selective catalytic reduction. The company says it plans to switch to SCR.

Two other Class 8 manufacturers that saw December sales fall from year-ago were PACCAR, down 10.9%, and Volvo Truck, down 12.7%.

Medium-duty deliveries rose 15.8% last month and 12.1% for the year on the strength of Classes 5 and 7.

Class 7 sales climbed 11.7% in December from like-2011 and were up 13.7% for the full year, with Daimler strengthening its lead over other manufacturers and passing International as the group’s top seller.

Daimler’s sales surged 29.2% for the year to 19,316 units, compared with International, down 11.2% to 13,796 in 2011. Daimler’s share jumped to 41.2% from 36.3%.

Both International and UD Trucks saw volume underperform from prior-year. UD Trucks was the biggest Class 7 loser, with December deliveries plunging 46.3%.

Class 6 sales rose 8.7% in December, but fell 1.7% for 2012. Ford and International were responsible for much of the year’s downturn. Ford was off 22.8%, while International was able to hold on as the volume leader with 15,884 deliveries in 2012.

Class 5 enjoyed the largest increase of any medium-duty group, up 29.2% for the full year. The segment’s December sales jumped 24.1%, also the biggest gain among the truck segments.

Daimler and its Class 5 brands saw triple-digit percentage increases for 2012. Ford deliveries soared 30.8% to 35,728 units, placing it well ahead of the pack. Chrysler increased its hold on second place for the year in Class 5, up 36.9% to 10,307, while International and PACCAR’s Kenworth lost volume.

Class 4 sales rose 10.5% in December, but dropped 9.8% for the year. Ford slid 44.6% and Daimler plunged 77.6%, compared with 2011. Isuzu strengthened its hold on the No.1 spot, increasing import and domestic deliveries in December as well for 2012. International also gained on year-ago, up 49.5% in full-2012.

Class 8 closed out December with a 50-days’ supply, or 34,959 units in stock, up from 41 days and 31,948 in 2011.

Days’ supply of medium-duty trucks slipped to 68 from 77 in like-2011, but inventory rose to 36,047 units from 35,081.

cschweinsberg@wardsauto.com