Last updated Friday, August 29, 2014 03:51pm

File picture shows Chrysler Group assembly worker Brenda Williams checking under the hood of a 2014 Dodge Ram pickup truck at the Warren Assembly Plant in Warren, Michigan, December 11, 2013. — Reuters picFile picture shows Chrysler Group assembly worker Brenda Williams checking under the hood of a 2014 Dodge Ram pickup truck at the Warren Assembly Plant in Warren, Michigan, December 11, 2013. — Reuters picDALLAS, June 29 — US auto-safety regulators are investigating complaints that rear axles on Dodge Ram pickups have locked up without warning while driving, causing vehicles to spin out at high speeds in some cases.

The National Highway Traffic Safety Administration opened the investigation after receiving 15 complaints describing the mechanical failure on the 2005 Dodge Ram 1500. Seven incidents occurred at speeds of 50 miles (80 kilometres) per hour or more, according to a posting yesterday on the agency’s website.

“A preliminary evaluation has been opened to assess the scope, frequency and safety-related consequences of the alleged defect,” the agency said.

There have been no crashes or injuries related to the complaints on Chrysler Group LLC’s truck. The probe involves about 260,000 vehicles, the agency said.

At least two of the complaints from drivers said the lockup of the rear axle made the truck spin. Consumers reported that loose pinion nuts caused the rear differential, which makes the back axle spin, to lock up, or caused the drive shaft to separate from the differential, the agency said.

Drivers said there was little noise or other warning before the lockups or separations happened, NHTSA said.

“Chrysler Group is cooperating fully with NHTSA and would like to remind customers that this is an investigation, not a recall,” the automaker said in an e-mailed statement. — Bloomberg