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I was told that I need to replace the shock absorber in my 1992 316i BMW. When I attempt to visit a web site to order the part it does not list any of parts with this name. I know nothing about cars and parts.

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What is a shock absorber?

I'm going to answer the basic title question with a carefully selected quote from the great Wikipedia:

... their intended sole purpose is to dampen spring oscillations.

Think of how you want your car to ride when driving down a smooth road that has a bump or pothole. You expect to feel a mild jolt when the car travels over the bump and then return to a smooth ride. The suspension uses two main components to provide this to you.

  1. A spring (as opposed to a rigid rod connecting vehicle to its wheel). This gives the suspension some flex to absorb the impact, reducing a painful impact to the mild jolt mentioned above.
  2. A shock absorber (also known as a damper). This damps the oscillation of the spring and handles the "return to a smooth ride" part.

Without the spring, every bump would hit your spine like a sledgehammer. Without the damper, the bouncing spring would continue down the road, making you seasick.

Now, your 316i apparently has McPherson struts. This part allows you to connect the spring and damper into one assembly:

The strut will usually carry both the coil spring on which the body is suspended and the shock absorber, which is usually in the form of a cartridge mounted within the strut

On a strut, the shock absorber cartridge sits inside the vertical tube of the strut while the spring rests on top of the wide collar. A strut top sits on top of the spring and is attached to the vertical shaft rising out of the tube.

So, if you mechanic is telling you that you need to replace a shock absorber, they almost certainly mean that you need to replace the strut, not the spring. Given the age of the vehicle, it would be a good idea to ask if the strut top needs replacing as well.

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It may be listed under "strut assembly" (either McPherson or Chapman, depending on which one you need). These days cars normally have struts. About the only place a true standalone shock absorber is seen anymore is on trucks.

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  • Trucks typically have leaf springs though which play the same role as struts
    – rviertel
    Commented Feb 9, 2018 at 7:09
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A shock absorber is a device that uses hydralic compression to absorb the impact when a car hits a bump or to help the car ride more smoothly.

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It keeps your car's springs from bouncing up and down uncontrollably when you go over bumps. It looks like a bicycle pump and actually works in much the same way.

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