Tacoma Shocks & Struts: Managing Overlanding Bumps

A shock and a strut are very similar, but are not interchangeable. They both perform one similar function, but the strut can do more.

The basic shock absorber does one thing: absorbs the bumps. A shock absorber is connected to the vehicle body on one end, and the axle on the opposite end. Both attachment points are cushioned with rubber bushings.

Struts, on the other hand, can perform multiple tasks; depending on the type of suspension they’re used in. The primary job of the strut is the same as the job of the shock: absorbing bumps.

There are numerous other jobs that the strut can do, based on the type of suspension they’re utilized in. In a suspension that doesn’t utilize the upper control arm, the strut assembly becomes a key structural component. It connects between the body and the lower control arm. Struts also support the coil spring, as the coil is placed around the strut body, and rests on the spring seat welded to the exterior of the strut body.

Finally, struts hold your tires in an aligned position. After setting the alignment, the strut keeps the wheel and tire in the correct position. Despite bumps and side force, the tire remains straight going down the road.

The shock absorber body, or exterior, is composed of two lengths of tube, with provisions for mounting at each end. One length is slightly wider than the other so that the smaller tube can fit inside the larger tube during compression of the shock. The narrower tube is sealed, while the wider tube is only capped on one end, serving as a protective cover. The wider end of the shock tube is connected to a long rod, with a piston on the opposite end. This fits inside the narrower tube portion. The inside is filled with a media, usually gas or hydraulic fluid.

The piston has seals around its circumference, which prevent any of the media from bypassing the piston. The most important detail of the shock absorber is located on the front of the piston, the valving. These tiny holes in the piston allow small amounts of media to pass through the piston, into the other side of the shock absorber.

The slow transition of fluid from one chamber to another provides the resistance and absorption of the bumps as you are driving. Shocks are also velocity sensitive, in that the faster the suspension cycles, the more resistance the shock provides.

The construction of a strut is similar, having the piston rod bolted to the mounting plate at the top of the strut and spring assembly, and a piston inside the tube on the other end. On the piston are the same sort of seals and valve holes. The major difference is that the strut assembly has provisions on the outside of the tube to hold and contain the coil spring, and a top plate that bolts in to contain the strut/spring assembly. The coil spring is compressed to a shorter than operational length.

Then, the bottom of the spring is aligned with the spring seat on the strut, and the top plate is located on the top end of the spring. A center nut is placed on top of the piston rod, and tightened. The coil spring is decompressed, and the nut holds the spring at its operational length and compression. The entire strut/spring assembly then bolts into the vehicle as a single unit.

The strut acts in the same sort of manner as a shock, while the coil spring supports the weight of the vehicle. Struts are also velocity sensitive.

Damping occurs when you drive over a bump or obstacle. The wheel and tire are forced upward, as is the piston in the shock absorber. The shock is physically compressed, or squeezed, between the lower control arm and the body, in order to absorb the upward energy from the bump.

Damping is how slowly or quickly the piston moves upward through the hydraulic fluid inside the shock absorber. Damping can be adjusted to cushion your ride over bumps at speed.

Rebound is just the opposite. When you drive over a rut or hole, the wheel and tire move downward. The shock absorber is extended downward, in an effort to keep the wheel and tire in contact with the ground. Rebound is how quickly the shock will force the piston downward, maintaining contact with the road. You can adjust rebound to give the maximum traction required at key points.

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.

While there are many different suspension options and upgrades available from Toyota, we’re going to focus on the most common setup. That would be the normal, or “base” suspension.

The front of the Tacoma is equipped with a basic, non-adjustable strut setup. The lower spring seat can only be placed in a single position, yielding no adjustments. 
The rear of the truck is fitted with monotube shock absorbers.

When in the market to level the front end of your truck via upgraded suspension, you’ve got two choices: upgraded struts with adjustable lower spring perches, or coil overs.

The upgraded struts have lower spring seats that have a few pre-determined adjustments. This will, in most cases, allow you to get the front and rear of the truck pretty close to level. These struts are very cost effective, running about $200 for a front pair.

The ride quality and handling will be improved, just not as much as with coil overs. This setup is geared toward the weekend warrior - a truck that might see fire roads on weekends but spends most of its time on pavement. Bang for buck is excellent here, though.

The top of the heap is the coil over. Its threaded body allows for almost infinite adjustability. You could literally use a level to set your front ride height. They provide superior ride quality, as well as improved handling and decreased body roll. The best doesn’t come cheap though. A set of front coil overs will set you back anywhere from $500 to nearly $2,000.

Like a shock eventually needs replacement, coil overs need rebuilding, but more frequently.  And at a cost of several hundred dollars each time. In states that use road salt, corrosion can also be an issue. Corrosion can cause the adjustable spring perches and the body to fuse, making adjustment impossible. The coil over can possibly be disassembled, lubricated, and freed. If not, replacement is necessary. If your Toyota spends most of its time in the dirt, this is the setup for you.

Strut top spacers are the easiest & cheapest way to lift, or “level”, the front of the truck. These spacers, constructed of various materials, bolt to the top of the strut assembly. By bolting the spacer in between the strut top and the vehicle body, it forces the suspension downward and creates more ground clearance beneath the vehicle.

Another option to lift the front of your Taco is lift shocks. Lift shocks are constructed with the lower spring seat in a higher position. This compresses the spring further, increasing preload, and provides lift. Both of these options create enough lift to level the front and rear of the truck.