Sales of medium- and heavy-duty trucks were flat in July, slipping a slight 0.7% from year-ago on declining deliveries recorded in three of the sector’s five groups.

Class 4, Class 7 and Class 8 drops tempered growth in Classes 5 and 6, WardsAuto data shows.

Class 8 sales slid 10.3% to 15,340 on a 34.0% plunge by Volvo Truck’s Mack Truck, and an almost 30% drop in International deliveries.

Keeping Class 8 volume from falling further were Daimler’s Western Star and the Volvo Truck brand, which posted increases of 31.9% and 31.3%, respectively.

Growth in Classes 5 and 6 propelled overall medium-duty sales to a 12.0% gain last month vs. like-2012, on 14,561 units.

Class 7 deliveries tumbled slightly, down 1.0%, as minor player Ford lost 33.6% of year-ago volume. Hino and Peterbilt also saw sales decline in July. Kenworth posted the biggest percentage rise in Class 7, up 23.4% to 297 units.

Sharp increases at nearly all manufacturers drove Class 6 results up 21.7% from like-2012.

Kenworth posted the biggest spike, with sales rising 166.0%, but it was volume-leader Freightliner’s 98.9% jump that had the biggest impact on the group’s overall results. International suffered the biggest falloff in Class 6, down 32.7%.

Class 5 edged out Class 6 for the biggest increase among big-truck groups in July, with sales jumping 23.2%. PACCAR notched the largest percentage gain, a whopping 548.0%, but on just 54 units.

Chrysler, up 133.9%, recorded the second-best Class 5 results, strengthening its hold on the No.2 market-share position, with a 26.8% stake, up from 14.1% year-ago. Ford is the segment leader, with a 58.0% share.

Mitsubishi Fuso, which posted the biggest drop in Class 5 (68.9%), also suffered the largest decline in Class 4, with deliveries down 36.7%. That slip, along with the 32.1% falloff in Isuzu’s imported models, was to blame for the 10.6% dip in Class 4 demand overall.

Through July, sales of medium- and heavy-duty trucks were tracking 3.0% behind year-ago’s pace, with 196,551 units.

Units in inventory and days' supply of both Class 8 and medium-duty trucks fell last month. Class 8 stock slid to 35,351, or 58 days, from 42,607 and 62 days in like-2012. Medium-duty inventory fell to 39,053 at the end of the month, or 67 days' supply, vs. 39,849 and 77 days’ year-ago.

In other big-truck news, Navistar says it will eliminate a “few hundred” jobs by early next month, reports the Chicago Tribune.

The Illinois-based truck maker blames a slower-than-expected restructuring for the job cuts, which should come from “support areas.”

Navistar also reports receipt of 10,000 orders for International trucks with Cummins’ ISX15 engine and Cummins’ selective catalytic reduction technology, seventh months after reintroducing the combination.

Navistar says demand for the 15.0L engine with the ProStar chassis prompted it to bring back the configuration. The engine also is available once again in International PayStar 5900 Set-Back Axle and 9900i models.

Orders were received from major for-hire and leasing fleets in the U.S., including Knight, Penske, Ryder and Swift, Navistar says. Last month, the truck maker said its share of orders for on-highway Class 8 trucks hit a 3-year high.

cschweinsberg@wardsauto.com