BAGHDAD - Part of quality preventative maintenance is looking for anything loose that shouldn't be and making the adjustment.

On humvees specifically, the bolts to the four half-shafts, two in the front and two in the rear, consistently need to be checked and tightened when necessary.

The four half-shafts act like axles for the humvee said Spc. Charles Marshall, a light-wheeled vehicle mechanic, from Wheeling, W.V.

"They are attached to the front and rear differentials. They convert power from the transmission to the wheels."

"All it takes is a 15mm wrench. Get underneath; if you can move those bolts with your fingers, you need to tighten those down," said Sgt. Michael Clark, a quality control and assurance shop foreman, from Arlington, Texas, assigned to Division Special Troops Battalion, 1st Cavalry Division.

Tight bolts on half-shafts are essential to a humvee's driving performance.

"It can cause damage to the brakes, you can lose steering," said Marshall. "There are about 30 different problems that can occur from losing a half-shaft."

Eventually, a tow may be needed. Bolts can break down the whole system; if you lose one half-shaft, you lose power to that wheel, dead lining the vehicle.

Bolts become loose for various reasons: general wear and tear, constant vibration from uneven roads, re-installments for upgrade purposes or work done to the brakes, said Marshall.

"Centrifugal force loosens the bolts over time, it's just something you can't help, you can tighten them as hard as you can all day long and eventually they still will come loose, whether it be a week from now or a month from now," said Clark. "This problem has been around since humvees have been around."

Mine-Resistant Ambush-Protected vehicles work differently than humvees when it comes to suspension systems.

MRAPs have solid axles. Half-shafts of humvees are independent axles. Soldiers are not able to check the bolts of the axles on MRAPs. They are completely encased, said Marshall.

Half-shaft bolts of a humvee are exposed making it easier for Soldiers to crawl under to verify that all 24 are tight, before rolling out. Checks under the hood, checks inside and outside the vehicle, and checks underneath the vehicle all count the same when it comes to preventative maintenance.