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You might have noticed going over potholes and bumps isn't as smooth as it used to be in your ride, which is probably a sign that your shocks are worn out and need replaced. A good easy way to test your shocks and make sure they're worn out enough to be replaced is to push down hard on the trunk or the hood directly above the wheel well. Good shocks should bounce up once and settle relatively quickly. If the body bounces any more than that after pushing, it's time for a new set. You also need to know if your vehicle uses stand-alone shocks that attach to the vehicle suspension or frame, or if it uses shock-absorber units which integrated into a suspension strut, such as the MacPherson or Chapman strut. Your car may even have a combination, using shocks in the front and struts in the back. Struts can be difficult to replace, so it's best to let a professional handle that job. If you're unsure what type of shock absorbers you need, speak to someone at your local auto parts store or an auto mechanic to be sure you buy the right shock absorbers or piston for your vehicle. You can get identical replacements of the shocks you have in your car currently, but taking the time to change out your shocks is also a good opportunity to perform any upgrades, if you're interested. Performance shocks are appropriate for heavy-use daily drive vehicles, especially trucks.   Coil shocks are manufactured with a coiled spring around the body of the shock, which supports the weight of the vehicle and controls the movement of the suspension. These are adjustable, which means you can alter the height of your truck for optimum performance.   Twin-tube shocks have a set of tubes, one inner and one out, that house the piston, along with a layer of shock fluid and air, which can have a tendency to create a foamy, frothy mixture that can affect performance, though some modern variations feature a nitrogen mixture that addresses the issue. These are common on off-road vehicles.   Monotube shocks feature a tube and two pistons, which work essentially like the twin-tube shocks work, with one piston separating the layer of nitrogen from the air. It runs cool and is a popular performance choice for trucks.   Reservoir shocks are filled with fluid, and either pressurized air or nitrogen. As the shock absorbs bounce, the fluid contacts the gas, causing resistance and dampening the spring action. Park your car on a level surface and loosen the lug nuts on both sides of the front or back end. Secure your vehicle with ramps and/or jack stands. Check your owner's manual for the correct jack positioning. When you've got the car up, remove the wheels and locate the shocks. Shocks will be affixed with a vertical bolt that has to be extracted from within the engine bay or the trunk, or may be positioned at the top by a horizontal bolt that has to be unfastened and knocked out of position. The most difficult part of the job is removing the old shocks, which can have a tendency to be really gunky with both age and road-grit, making the bushings and bolts somewhat difficult to remove. Check out the mountings to see if they're loose enough to get off, or if you're likely to crack the rubber around the bushing. It's ok if you do, since you're changing out the shock anyway, but it's usually easier to spray some WD-40 or PB Blaster in there and let it sit for a few minutes to try to loosen things up before you get to work.
Make sure you need new shocks. Purchase new shock absorbers. Consider upgrading your shocks. Jack your vehicle in an appropriate location. Check the shock mountings and spray them with metal cleaner.