See Figure 1
The jack supplied with the truck is designed for changing tires. It should NOT, nor should any jack, be used to support the truck while you crawl under it and work. To do so is to recklessly jeopardize your life. Whenever it is necessary to get under a truck to perform service operations, always be sure that it is adequately supported using jackstands at the proper points. Always block the wheels when changing tires.
If your truck is equipped with a Positraction rear axle, do not run the engine for any reason with one rear wheel off the ground. Power will be transmitted through the rear wheel remaining on the ground, possibly causing the truck to drive itself off the jack.
Once the jackstands are in position and the vehicle's weight has been lowered onto them, shake the truck a few times before crawling underneath to make sure the jackstands are securely supporting the weight.
Service operations in this information often require that one end or both ends of the truck be raised and safely supported. The ideal method, of course, would be to use a grease pit or hydraulic hoist. Since this is beyond both the resource and requirement of the do-it-yourselfer, a small hydraulic, screw or scissors jack or floor jack will raise the vehicle sufficiently for almost all procedures in this guide. The rolling floor jack is probably the easiest and most convenient of these to use. But the vehicle must still be supported by at lease two sturdy jackstands if you intend to work under the truck at any time. An alternate method of raising the truck would be drive-on ramps. Be sure to block the wheels when using ramps. Spend a little extra time to make sure that your truck is lifted and supported safely. Remember, the truck you are under weighs at least 1 / 2 ton.
Regardless of the method of jacking or hoisting the car, there are only certain areas of the undercarriage and suspension you can safely use to support it. The front and rear crossmembers and the side frame rails and generally safe areas by which to support these vehicles. But be careful not to contact and damage other components such as stabilizer bars or the exhaust system. Also, it is advisable to protect the vehicle's undercarriage from scratches that will promote corrosion. To help prevent unnecessary scratches a block of wood should always be positioned between the jack or jackstand and the vehicle. Be especially careful that you do not damage the catalytic converter. Remember that various cross braces and supports on a lift can sometimes contact low hanging parts of the car.