Following are the different types of shocks and struts featured on Toyota Tacomas.
Twin Tube: A twin tube shock absorber is constructed of the outer tube, as well as two smaller tubes against the inside walls of the main tube. There is also a compression valve inside the main tube, at the bottom of the shock. When the wheel moves up and down while traversing terrain, the piston forces the fluid to move between different passages inside the shock absorber, through small holes in the piston and compression valve.
There is also a second variety of twin tube shock absorber, a gas charged twin tube. It is constructed similarly to the twin tube, but pressurized gas is added to the smaller passages inside the main tube. This adds both more pressure and resistance to the hydraulic fluid inside the shock, as well as helping to prevent overheating and leakage. These are the most likely to be original equipment on vehicles today.
Position Sensitive Damping: Position sensitive damping is constructed in the same manner as the twin tube shock, with a large center chamber that the piston moves in. The “PSD” also has the two smaller tubes on either side and the pressurized gas charge.
The difference here is a series of grooves added to the outside wall of the main tube. This allows fluid to move more easily inside the shock within an average, or most typical, range of travel. As the piston moves further and more frequently, the piston moves beyond the added grooves, providing more resistance.
This provides more comfort and control for the driver during changing environments. This design change also allows for a more customized shock absorber, for a specific make and model. The shocks can be properly constructed to compensate for a vehicle’s weight, horsepower, and handling characteristics.
Acceleration sensitive damping: The acceleration sensitive damping, or “ASD”, shock is constructed the same way as the position sensitive damping piece, but with a change in design on the compression valve. This allows for a more instant reaction to individual bumps. This design also helps to prevent pitching during breaking, and body roll during cornering.
Coilover Shock: A coil over shock is very similar in appearance to a strut, but very different in function. The coil over consists of an adjustable twin tube shock absorber with a body that is threaded on the outside. There are threaded, adjustable perches that screw onto the outside of the shock body. The coil spring goes around the shock body, and rests on the perches. The perches are located with adjustable nuts that are tightened to hold them in place. This allows for almost infinite adjustment of ride height, spring pre-load, shock damping, and rebound.
Mono-Tube: The mono-tube shock absorber is constructed of a single tube in which the piston attached to the piston rod moves. There is a second piston inside the shock absorber that separates the hydraulic fluid from a high-pressure gas charge. The two pistons move in harmony, depending on terrain changes. The high-pressure gas charge inside the mono-tube shock absorber also does something that no other shock does. It helps to support the body of the vehicle.
Spool Valve: Spool valve shocks rely on hollow cylindrical sleeves, with machined in oil passages, as opposed to the disc style valving of the others. This type of shock can be a sub-variety of twin tube, monotube, or position sensitive units. They can also be part of an electronically controlled suspension. The machine work to the sleeves allows for a more repeatable, predictable response.