Everyone knows that suspension is crucial for a fast lap time or even basic chassis control. The importance of your shocks to your overall quality of suspension is huge, yet many racers don't spend nearly enough time on their oil filled traction-makers. A smooth, matched, bind free set of shocks will force your chassis to clamp onto the racing surface and act as if it never wants to let it go, while still maintaining the consistency and grace of a perfectly balanced ballerina (as if we know what a perfectly balanced ballerina looks like). Enough about chicks dancing on their toes; keep reading to find out how to build the ultimate shocks for your ride.

Issue 158 - January 2009)

Words: Jeff Eveleigh

Before you even think about getting started on your spring-wrapped wonders you need to set up an adequate workspace. Lay all of your shock parts out on a clean rag, towel, or pit mat. Using a sharp hobby knife, carefully trim all of the plastic parts away from the parts tree. Make sure that you remove all mold flashing, but be careful not to remove too much material and alter the shape of vital components such as shock pistons and shaft bushings.

Here are some tips that can be used during most shock assemblies (follow your kit instructions for specific assembly of your brand of shocks). Some shock pistons attach to the shock shaft with a screw use motor spray to clean this screw and the threads in the shock shaft and then use blue or even red thread-lock to secure the piston. (I almost never recommend red thread-lock in this hobby, but some shock shafts need it to keep the pistons locked in. Check with your manufacturer to see if they recommend permanent thread-lock for their specific shocks.) Coat all of your o-rings and shaft bushings in Green Slime,' which is available from Team Associated (Part # ASC1105). This thick grease will help prevent oil from leaking around your delicate seals. Always "wet" your o-rings with a drop or two of shock oil before you push the shaft through the seals at the base of your shock bodies to prevent tearing an o-ring upon insertion.

Why do some shocks have a bladder or a chunk of foam in them? There are many different shock designs, but they all work along the same principles. Fluid doesn't compress very much, so once your shock shaft enters your shock body the displacement of the shaft will eventually cause a hydraulic lock. There must be some sort of volume compensation to take up the slack from the non-compressing shock fluid to allow your shock shaft to fully utilize its travel. Air molecules are much less dense than fluid, so air compresses much more easily. Emulsion shocks allow shock oil and air to mix together to provide the volume compensation, but this can cause less consistent results since air can pass through the holes in your piston and produce erratic damping. That is where the rubber bladders or closed-cell foam come into play. The bladder or foam keeps air separated from your shock oil. As the pressure builds within your shocks, the air within your bladder or foam compresses and compensates for the extra volume of your shock shaft. This allows your shock to utilize its full range of motion. This pressurized air is also what causes "rebound." When you push your shock shaft all the way into the body it should push itself back out slightly once you release the shaft. This is the pressurized air releasing and forcing the piston and shock shaft back out in the opposite direction. Rebound, or at least matching your rebound is vital in building race winning shocks.

Once your shocks are fully assembled they are ready for oil. This is the most important aspect when it comes to building the perfect shocks, since matching them from left to right is a must for maximum performance. Pour the same oil into both shock bodies, then slowly pump the shock shaft and piston up and down a few times to remove the trapped air from beneath the piston. As you are pumping the shaft and piston you will see air bubbles emerge from the piston holes and rise to the top of the oil. Rotate the shock shaft as you are pumping to ensure that all air is removed from beneath the piston. Once all of the air bubbles have escaped from the oil you can top up the shock body with oil and thread on the shock cap (different shocks assemble in different ways, so check your specific instructions to find out the manufacturer's tricks). Push the shock shaft in all the way to make sure there isn't a hydraulic lock and also to check how much and how fast the shock shaft pushes back out from within the body. As already discussed, this action of the shaft being forced out of the body is called the "rebound," and this is what you are trying to match between shocks.

Once you are happy with the rebound characteristics of the first shock your next job is to match your other shock so it rebounds with the same speed and distance as the completed one. Finish adding oil and threading the cap onto the second shock and check the rebound. If you are lucky it will be exactly the same as the first shock, but if it isn't you will have to do some further tuning. If the shock you are working on now rebounds faster and farther than the first shock, you need to remove a tiny bit of oil. You can do this by unthreading the shock cap slightly (a few turns) and pushing the shock shaft in a little bit until a small amount of oil bleeds out around the shock cap threads. Tighten the cap on again and check the rebound. Continue with this procedure until both shocks have equal amounts of rebound. If the shock you are working on doesn't rebound as quickly or as much as the completed shock, add some oil to it. Remove the shock cap and place a few more small drops of oil into the shock body and go through the verification process again. Continue adding or bleeding oil from the shocks until they rebound at the same rate.

If you can't get the speed and rebound distance between the shocks to match regardless of the amount of oil you add or bleed, you have a deeper problem such as a binding shock shaft. You'll have to go back to the initial building process to solve this problem before you attempt to match rebound with oil again.

As a final pressurization check to ensure that your shocks are completely matched with regards to shock oil volume and shaft motion, hold a shock by the shock cap in each hand and butt the two threaded ends of the shocks shafts against each other so they travel along the same plain (just like one long shock shaft with threads in the center). Use your hands to push the shocks towards each other and force the shafts into the shock bodies. Both shafts should move at the same rate, and they should both bottom out within the shock bodies at exactly the same time. When you pull the shocks away from each other both shock shafts should rebound at the same speed to the same distance. If all of this occurs, you have a matched set of shocks. If it doesn't. go back to the start of this section and go through the process again.

With all this adding and bleeding oil out of your shock it's going to get a little messy. The oil that you bleed out around the cap will remain around the shock body and attract dirt once installed on your car. After you've fully matched your shocks, use some o-ring safe motor spray and give your shocks a quick hit to remove any oily residue left from the building process. This not only keeps them shiny and clean but allows them to perform bind-free as well.

Now that you have your oil and rebound matched perfectly your job isn't done yet. The physical length of your shocks must be matched as well. Thread on your ball cups using the end of the treads on your shock shaft for guidance. Use calipers to measure the overall length of your shocks from mounting hole to mounting hole and adjust the threading of the ball cup to match the lengths perfectly from left to right.

Your springs are important when it comes to building the ultimate shocks too. Most springs are matched well, but some manufacturing processes can cause slight tolerance differences. Use your trusty calipers to measure the overall length of your shock springs and try to get a pair that are exactly the same length. Use whatever measuring device you prefer to check the preload spacing as well since this is easy to mismatch, especially when using threaded shock bodies.

Always build and rebuild your shocks in pairs (as in left and right shocks together). You will have a really hard time matching your shocks if one of them is bound up from poorly trimmed mold flashing or if one shock has fresh o-ring seals while the other doesn't. If one shock is leaking and needs new bushings and seals, replace the parts in the opposing shock as well. If you get into the habit of wrenching on your shocks in pairs you'll never have to worry about two mismatched tubes filled with oil. [sb2]

Check the suspension components on your chassis to be sure they are equally free of binding from left to right. Before installing the perfect pair of shocks onto your chassis, do a little investigative work to ensure it's ready. With the tires, rims, and shocks removed from your car hold your suspension up and allow it to drop. The suspension arm and assembly should drop freely without any resistance. If it doesn't do this you need to start shimming, removing shims, cleaning, reaming, or grinding until it does. You also need to ensure that both the left and right suspension movements feel similar so that when you install your matched shocks the overall suspension works equally from left to right. Once you know that everything is acting the same, bolt on your shocks and go win some races.

By now you should have a strong understanding of how to build your shocks to be smooth, free, and matched. However, it is important to remember that your shocks will take a beating on the race course, so constant attention is needed to keep them in top performing order. Crashes, bends, and leaks can alter your precise assembly work, so yank your shocks from your machine from time to time and verify that they are still worthy to be bolted onto your race car!