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With (standard) spring shock absorbers like this one:
What's inside the body of the piston part? Is there some kind of fluid inside or is it just air and empty space for the piston to thrust into?
Is it the spring that bears all of force whilst the piston shaft is merely there to position the spring?
Thanks
The shock you have shown is called a "coil over shock absorber". The shock which is located in the center of the spring, functions just like any other shock absorber. It will most likely have hydraulic oil with baffles. It may or may not be gas charged. The shock casing is made stronger than a regular shock, mainly to support the spring. You'll also notice the threads on the body, which makes it adjustable. You can vary the ride height of your vehicle by screwing the spring perch up or down on the shock body.
The real reason for this type of shock is to eliminate the stock spring on a vehicle. This makes for a more compact fit within the footprint of what would normally just be the shock. It might allow the owner to put a different type of axle under the vehicle or allow space for wider tires. It might also just be used for an aesthetic look the owner is going for.
To expand upon Paulsters answer, the middle part is often called a damper in the UK as often as it's called a shock absorber.
Which is a good word as it dampens the springs. Ideally, the weight of the car sits on the spring part, but without the shock you'd be bouncing up and down for the whole journey! So the damper simply dampens the spring back to neutral. A quick test to tell if your shocks are damaged is to push down on the corner of the car and it should just bounce up once, if you get some bobbing then they're probably worn... Or you have a non German spine breaking ride!
