The semiconductor shortage is short-circuiting heavy-duty truck production as supply-chain disruptions hamper efforts to meet robust demand for new big rigs.

North American production of Class 8 trucks, the big vehicles that haul most domestic freight, sank this summer to its lowest level since May 2020, when the coronavirus had shut down much of the U.S. economy. Equipment makers built 14,920 units in July, the most recent month for which figures were available, while the backlog of trucks ordered but not built nearly tripled from the same month a year ago, to 262,100, according to transportation data provider ACT Research.

The production problems began earlier this year and have persisted for months, driving up the cost of used heavy-duty trucks and straining supply lines ahead of the fall, when fleets typically place big orders for new equipment.

North American trucking companies, pushing to expand capacity to meet strong freight demand, ordered 36,900 heavy-duty trucks in August, the highest level in five months and up 90% from the prior-year period, according to preliminary figures from ACT.

“Everything you want to see for Class 8 demand is there in spades,” said ACT President and Senior Analyst Kenny Vieth. “What’s missing are parts.”

The global chip shortage has caused auto manufacturers to slash car production, including new cutbacks announced this week by General Motors Co. and Ford Motor Co. , and is cascading through factories making heavy-duty trucks. Some equipment makers are moving semiconductors from smaller medium-duty trucks to Class 8 production to maximize the value of the chips, Mr. Vieth said.

While in the past “we simply ordered and received parts, we’re now reaching far down into our supply chain to assist suppliers in planning for shortages, navigating constraints, and working to help them keep the upstream flow of parts moving,” said David Carson, senior vice president of sales and marketing at Daimler Trucks North America LLC, whose brands include Freightliner.

The company is working closely with dealers and customers “to communicate clearly and frequently regarding the status of their orders,” Mr. Carson said.

A spokeswoman for Lisle, Ill.-based truck maker Navistar International Corp. said the company has “been experiencing the same challenges as the rest of the commercial truck and automotive sectors.”

Raw materials shortages and global shipping bottlenecks are also crimping availability of other components like wiring harnesses, truck mirrors and parts made of plastic, said Don Ake, vice president of commercial vehicles at transportation research firm FTR. “On any given week some of these are fine, and then the next week there are new ones,” he said.

Some truck makers aren’t yet booking orders for next year because “component costs are so high right now that it’s difficult for them to quote a good price where it’s profitable for the company but not excessive for the customer,” Mr. Ake said.

The tight labor market is also affecting domestic suppliers that make everything from small components to truck trailers, he said.

Walkouts by unionized workers earlier this year at a Volvo Trucks North America factory in Dublin, Va., disrupted production for weeks. A spokeswoman for the division of Swedish vehicle maker Volvo AB said the factory has been able to avoid supply-related downtime since the strike was resolved in July.

“The plant has been running on two shifts,” she said. “We are working closely with our suppliers to minimize the impact on our customers.”

A global chip shortage is affecting how quickly we can drive a car off the lot or buy a new laptop. WSJ visits a fabrication plant in Singapore to see the complex process of chip making and how one manufacturer is trying to overcome the shortage. Photo: Edwin Cheng for The Wall Street Journal The Wall Street Journal Interactive Edition

Write to Jennifer Smith at jennifer.smith@wsj.com