Magazine article National Defense

Medium Tactical Truck Failure Gets Quick Fix from Texas Contractor

Magazine article National Defense

Medium Tactical Truck Failure Gets Quick Fix from Texas Contractor

Article excerpt

Rapid action by the U.S. Army and industry appears to have averted a shutdown of its new medium tactical truck fleet and the indefinite postponement of a contract worth nearly $16 billion during the next three decades.

At issue are 2.5 and 5 ton tactical trucks produced by Stewart & Stevenson, Sealy, Texas. The problem, according to company officials, is a vibration in the driveline that is not unlike 200-pound jackhammers battering the vehicle's universal joints.

Army officials identified the shortcoming earlier this year. Both Stewart & Stevenson and the Tank-automotive and Armaments Command (TACOM), Warren, Michigan, subsequently moved quickly to find a solution, which in essence is the application of an engine cradle support bracket to dampen the vibration and the installation of replacement universal joints with improved design nylon thrust washers.

Dennis E. Mazurek, TACOM's deputy project manager for medium tactical trucks, in an interview, suggested that the cradle solution is appropriate for current vehicles. He said in the longer term, however, re-engineering vehicle components probably will be the way to go. Mazurek specifically mentioned the flywheel housing.

Initial press reports grossly overstated the number of mishaps caused by the drivetrain resonance. Mazurek said in fact only three occurred. One involved a rollover-when a vehicle flips 180 degrees. Another resulted in a truck tipping onto its side, and the other ended in a safe stop. He said none of these mishaps resulted in "severe injuries." These malfunctions took place on hard highway surfaces at the high end of the vehicles rated speed.

Stewart & Stevenson tactical trucks, which are designed to travel both on open ground and on pavement, have a top speed of 60 miles an hour.

The Army, Mazurek said, ordered users to drive no faster than 30 miles an hour following discovery of the drive shaft failures. The service conducted its own tests of the cradle bracket both on and off road-with about 80 percent of the inquiry focused on highway driving.

At this point, the cost of the bracket is not known, but officials estimate that it probably will be in the neighborhood of $200. Also, undetermined is who will pay for this modification. Mazurek suggested that the Army would not assume this added expense.

Laroy Hammer, Stewart & Stevenson senior vice president, meanwhile, told National Defense that the "driveline issue was an unforeseeable event. …

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