Coilover shocks have grown immensely in popularity amongst four-wheelers, mud-boggers, and rockcrawlers in the last 10 years, and for many good reasons. What started out in the desert racing world is now a mainstay that seems to be on all the coolest rigs on the trail.
To simplify things we must understand that every suspension needs a spring to support the weight of the vehicle and a shock to control the movement of the spring. The more adjustability you have of both the spring and the shock, the more you can fine-tune your suspension. Coilover shocks are inherently adjustable.
In addition, coilover shocks are easy to mount. Whereas a coil or leaf spring suspension requires separate mounts for the leaves and shocks, a coilover shock just needs an axle and a chassis mounting point (albeit you will need all the links to locate the axle, but that's a given for any coil suspension).
Now as much as we like coilover shocks, we'll gladly admit that there is still a place for leaves and separate coil and shock suspensions. They are much cheaper than coilovers, they can be made to work pretty darn good in their own right, and they work great 95 percent of the time. It's just that last 5 percent that we'll be exploring this month with our coilover shock investigation. Also, you can get rebuildable shocks very similar to coilover shocks that can be revalved in the same way we will show revalving a coilover.
 1. Most coilover shocks such... 1. Most coilover shocks such as this 2.5 piggyback reservoir are rebuildable, meaning the valving inside can be adjusted for performance over different terrain. This shock has a internal floating piston (IFP) inside the reservoir that separates the oil in the main shock body from a charge of nitrogen. The nitrogen is held at around 200-250 psi, and this keeps constant pressure on the oil so that it doesn't aerate (foam up). |  2. This Fox 2.0 emulsion coilover...  2. This Fox 2.0 emulsion coilover is also rebuildable, but since it doesn't have a remote or piggyback reservoir it doesn't have an IFP to separate the oil from the nitrogen charge. Though still a great shock, there is the possibility of aerating the oil during high speed. If you have the choice and the change, go for an IFP or reservoir shock. |  3. Tuning your coilover shocks...  3. Tuning your coilover shocks is different for every make and model of rebuildable shock on the market, but we'll show you a simple adjustment to a Fox 2.0 emulsion shock. Along with a clean room to work in, one of the most important things for rebuilding shocks is a sturdy vise with a set of soft jaws. You can either make your own out of aluminum or bronze or order a set such as this aluminum version from Poly Performance. |
 4. The first step in breaking...  4. The first step in breaking down a coilover is to release all the nitrogen pressure from the shock. Be sure to hold a rag over the Schrader valve when you depress it to keep any oil from spraying out. |  5. Next, loosen the set screw...  5. Next, loosen the set screw and unscrew the seal carrier cap with an adjustable-face spanner wrench to get access to the snap ring that holds the seal carrier in place. You will need to press down on the seal carrier in order to get the snap ring out. |  6. Now you can remove the...  6. Now you can remove the shock shaft with the seal carrier and piston installed. You will want to save the shock oil in a clean container for reuse. If the oil smells burnt it's probably time to replace it. |
7. On the shock shaft is a piston with shims on either side. As the shock compresses and rebounds, the piston moves through the oil inside the shock body and the oil is forced through holes in the piston that open up against the shims. Here the red wire represents the oil moving through the piston. The shims have been loosened to show how the oil flows.
8. The oil flows faster or slower depending on the thickness of the shims in the stack. Changing to thicker or thinner shims determines whether you have heavy or light compression or rebound. Thinner shims mean an easier flow, a faster-moving shock piston, and less restriction or control over the suspension and axle movement. The Fox Shocks shim kit includes various shims thicknesses and a sheet to explain what shims to use for your desired valving weight.
 9. From left to right you...  9. From left to right you have your shock piston parts. These include the retaining nut, washer, rebound stack, piston with Teflon wear band, compression stack, washer, rate plate, seal carrier, and seal carrier cap (last four items still on the shock shaft). |  10. With the piston reassembled...  10. With the piston reassembled you'll notice that the shims cover all the large flow ports exit holes, but there are usually one or two small round holes in the piston. These bleed holes are where the oil flows during slow wheeling, such as light cruising or slow rockcrawling. |  10. With the piston reassembled...  10. With the piston reassembled you'll notice that the shims cover all the large flow ports exit holes, but there are usually one or two small round holes in the piston. These bleed holes are where the oil flows during slow wheeling, such as light cruising or slow rockcrawling. |
The Rest Of The Story
Making your coilover shock work best for your application is done through adjusting the coil spring rates and the valving, but knowing exactly what spring rate and valving you need is almost a black art. It is important to find a dealer who will deliver the valving and spring rates for your vehicle. A good dealer will ask what you are building, the type of terrain you want to drive on, and the sprung and unsprung weight of your 4x4, then build or recommend a coilover built to your spec. This won't be perfect, but it should get you in the ballpark.
Final tuning may be required. Many shock companies or private shock tuners can do this for a fee, or you can attempt it yourself. Just keep good notes of what you started with so you can always return to that starting point, and you'll need the tools mentioned in this story. As a most basic rule, you'll want heavy compression and light rebound for a go-fast truck so the axle follows the terrain and soaks up big hits, or you'll need a light-compression, heavier-rebound shock for rockcrawling, because in rockcrawling you need easy articulation but don't want the truck to kick off the rocks.
Like all rules, these have exceptions. Check out Fox Racing's "Tuning Tips" (www.foxracingshox.com/fox_tech_center/tuning_tips.htm) for additional info. Though Fox focuses on its bicycle division, the info is helpful for any shock-equipped vehicle.
The perfect valving is different for every truck and shock style used, but like fuel injection tuning, tire pressure adjustment, and even link suspension geometry, it takes time to get the best riding and driving vehicle for your type of wheeling.