Orders for Class 6 through 8 trucks dropped from March to April.

ACT Research Co. predicts the final numbers, which will be released mid-May, will approach 17,200 units for heavy-duty Class 8 trucks and 8,600 for Class 6-7. The preliminary net order numbers are typically accurate to within 5% of actual.

FTR Associates released similar preliminary data, showing April Class 8 truck total net orders at 16,877 units, the lowest number since September 2010 and 55% below the same month a year ago. April orders continue the downward trend in Class 8 orders for 2012, with annualized units for the past three months now at 234,600, FTR says.

"Orders continued to come in below the level ultimately needed to sustain current rates of build," says Kenny Vieth, president and senior analyst. "Conditions that contributed to the soft patch that started in March were still in play in April, including higher diesel and new truck prices.

"Beyond that, the data that we use to predict demand remain healthy," Vieth says. "The overall economy, and in particular the manufacturing sector, continues to grow, trucker profits are healthy, and used truck prices remain close to record levels."

FTR President Eric Starks called the four-month trend significant. "It is causing many in the industry to question their assumptions of growth for 2012. Now that we are through the typical ordering season we expect orders to remain in the sub-20k level through the summer months," which could mean OEMs needing to scale back production later this year.

However, Peter Nesvold, transportation analyst with investment banking firm Jefferies & Co., says while the order trend suggests demand slowdown, "fundamentals point to a pause."

Although a slowdown in orders and moderating freight growth suggest that industry demand could be slowing, he says, "end customers remain profitable, the fleet is exceptionally old, and freight growth remains positive. A surge in orders late last year ahead of new model year price increases combined with the strong fundamentals lead us to believe that the current order weakness is a pause before reacceleration in coming months. Still, unless orders begin to recover soon, our 300k production forecast (and some company outlooks) could be at risk."