Custom Valving Sway-A-Way RaceRunner shocks
Published by Trails Less Traveled on May 10th, 2004
INTRODUCTION
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Even the most expensive shocks will only perform to their potential once they are properly tuned for a specific vehicle and intended use. High-end shocks bought off-the-shelf come with neutral valving that is suitable for a variety of applications. Ideally though, every shock would be custom-tuned, and luckily, adjusting the valving of high-end shocks is relatively easy. Really, that’s what we are paying for in these $300+ shocks. It’s a simple process, and only a few common tools are required (along with any parts to be replaced, like shims-stacks, seals and new fluid, etc.).
It can be really helpful to consult with an expert when it comes to shock valving. We contacted Mike Arthur for tuning advice, and talked with him about the vehicle weight, suspension type, intended use, etc., in order to determine the proper valving for the Tacoma. Mike Arthur makes his living tuning and rebuilding racing shocks for top desert-racers, and his experience has allowed us to get a lot closer to optimum performance out of our shocks than we could have managed alone.
Once Mike Arthur had helped us to select the proper shim-stacks for our shocks, we called Mike Livingston at Kartek to order all of the parts we needed. Kartek carries all of the parts required to rebuild and tune your Swayaway, Fox or Bilstein shocks, and they usually have them in-stock. We ordered a variety of 56 valve-shims, and two gallons of 7wt Torco shock fluid.
SUSPENSION TUNING GOALS
We first installed the Total Chaos long-travel front suspension on the Trails Less Traveled Tacoma using a pair of Sway-A-Way 8’ stroke coil-over shocks. The 2.5’ remote reservoir shocks could have easily served as the primary dampening up front, but we recently added a pair of Swayaway 3-tube bypass shocks up front to explore the performance of position sensitive dampening. With the added dampening, it became necessary to re-valve the coil-over shocks significantly softer.
The rear shocks were originally custom-valved by Swayaway for the weight of a stock Tacoma pickup truck, but we have replaced the heavy steel stock bed with light-weight fiberglass bedsides and roll-cage tubing’ causing the rear suspension to become stiff as a board and sit 3’ too high. We headed down to Deaver and had Erik custom tune our leaf spring pack to address the height and spring rate, but still needed to take some of the valving out of the rear shocks.
SHOCK REBUILDING & RE-VALVING
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Any shocks that need to be rebuilt/re-valved must first be removed from the vehicle. The front-end of the truck had to be raised enough to unload the front suspension. But before working on the vehicle, measure the amount of pre-load on the coil springs to insure that the ride-height and alignment can returned to the same settings when the shocks are reinstalled. We put the Tacoma up on a hydraulic lift, but a tall floor-jack and jack-stands would work just fine in the driveway at home.
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Once the vehicle is lifted and properly supported, the nitrogen can be removed from the reservoir by depressing the Schrader valve core. Remove the pre-load from the coil springs, then take out the lower coil-over shock mounting bolt and remove coil springs (as shown in the image on the left). The coil-over shock can then be easily removed from the truck.
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To remove the rear shocks, we just depressurized the nitrogen chamber and unbolted them. It’s not necessary to raise the rear of the truck, because the rear shocks on a leaf-spring suspension do not support any weight.
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IMPORTANT: MAKE SURE THE NITROGEN IS DISCHARGED
First, remove all (upper & lower) heim misalignment spacers and set them aside. Place the shock upside down in a bench vise, secured by upper the shock mount. Make sure to use soft jaws (plastic, aluminum, etc.) to save shock from damage. Then remove the three allen-head bolts from the dust wiper seal housing and slide the dust wiper up the shaft and out of the way.
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Cycle the shock shaft to full extension to help avoid spilling any shock fluid when removing the shock shaft and piston. Depress the seal housing with gentle pressure to expose the retaining circlip, and then remove the circlip.
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Tie a clean shop rag around shock body to catch any shock fluid that overflows while disassembling the shock. Start to remove the shock shaft by pulling up slowly on the shaft and lower shock mount (the lower shock mount will be on top because the shock is mounted in a vise upside-down). Take care not to force it or pull too hard/fast because the suction of the seal can cause the shock shaft to spill shock fluid everywhere. Once the shaft is completely out the shock body, the seal housing, bushing and O-rings seal are readily visible. Carefully remove the shock body from the bench vise and either discard the used shock shock fluid, or reserve it to be re-used.
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Secure the shock shaft in the bench vise by the lower shock mount and then remove the shim-nut. Two out of our four shocks unthreaded at the shock mount before the shim-nut came loose (most likely due to a lack of thread-locking compound on the shock mount fitting). So we had to use machinist v-blocks to secure the shock shaft in the vise without damaging it, and use an impact gun to vibrate the shim-nuts loose. It is acceptable to use an impact gun to remove stubborn shim-nuts, but it is NOT okay to use air tools to install them.
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Once the shim-nut is removed, lift the piston off of the shock shaft, being careful not to lose any of the shims. Notice the various holes in the piston (visible in the image on the right with the shims removed). These holes allow shock fluid to flow through the piston as it cycles through compression and rebound. The rebound shims are on the topside of the piston (by the exposed threads), and the compression shims are located on the underside of the piston. Shim-stacks control the amount of shock fluid flow and are available in a variety of diameters and thicknesses to provide the proper shock fluid-flow rates for any application. As fluid force is generated and applied to the shims, they flex out of the way to expose the holes that allow shock fluid to travel through the piston.
Three holes around the shock-shaft on the flat part of the piston provide shock fluid flow to the rebound shims. They are completely covered by the rebound shims when assembled (image on left), and are shown exposed in the image on the right with the shims removed.
There are three smaller threaded bleed-screw holes located on the topside/rebound side of the piston. When a bleed screw is removed, the piston can pass fluid freely both ways (compression & rebound) through that orifice. Conversely, if all three bleed screws are installed, the shock can only pass shock fluid through the compression and rebound shims.
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The nine holes on the topside/rebound side of the piston (around the perimeter in groups of three) provide shock fluid flow to the compression. They come together as three large oval holes on the underside/compression side of the piston. (visible in image on right with the shims removed). These oval holes are completely covered by the compression shims when assembled (image on left), and are shown exposed in the image on the right with the shims removed.
The three additional oval holes on the underside/compression side of the piston provide shock fluid flow to the rebound shims. Although they are partially covered by the compression shim-stack, shock fluid is directed to the rebound shims by way of the step-milled slots closer to the outside edge of the piston.
We replaced the old shims with the new shim-stack that Mike Arthur recommended for our application, and then re-installed the piston on the shock shaft. Be sure to re-use the washers on the compression and rebound shim-stacks, and then re-fasten the shim-nut.
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The Schrader cap assembly must be removed to set the floating piston depth in the remote/piggyback reservoir. Depress the Schrader cap assembly to expose the retaining circlip. Remove the circlip and slide the Schrader cap out to expose the floating piston.
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If there is shock fluid visible in the nitrogen side of the reservoir, then there is a bad seal that needs to be replaced. It would have been helpful to have a new kit on-hand for this reason. But we didn’t think to order these parts ahead of time, so we had to wait for them to show up after we ordered them. Luckily, Kartek had all of these rebuild parts in-stock and had them to us by the next day.
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The floating piston in the reservoir must be reset to the proper depth as described in the Sway-A-Way service manual that comes with all of their shocks. Setting the proper piston depth is CRITICAL, and is dependant on the size of the reservoir. On 6’ reservoirs (Like our front shocks), the piston depth is set to 3.25’ (measured from the highest point on the piston to the edge of the canister). On 12’ reservoirs (Like our rear shocks), the piston depth is set to 9’ (measured from the highest point on the piston to the edge of the canister). If the piston depth is not set correctly, it can cause the shock to hydro-lock.
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Sometimes the piston is hard to move precisely because of the tight tolerances, and it can be pushed too far down inside the reservoir. If this happens, you will need to gain access to the other side of the piston. To do this on a piggy-back shock, remove the four allen-head bolts that secure the reservoir to the shock body and then remove the reservoir as shown above. On remote reservoir shocks, you can simply press-in the hose-end of the reservoir to set the piston to the correct depth. Once the Piston is set to the proper depth, replace the Schrader cap and circlip.
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It is now time to refill the shock with fresh shock fluid. Depending on the type of shocks to be filled, the procedure varies slightly. The goal is to get all of the air out of the shock fluid chamber. With remote reservoir shocks, the recommended procedure is to hold the shock upside-down and let the reservoir hang freely below the shock. This allows gravity to draw the shock fluid down while causing air bubbles to rise up through the shock fluid and escape. With piggy back shocks where the reservoir is permanently fixed to the main shock body via a 180? elbow, it can be a bit trickier since there is no easy way to use gravity to help air to escape.
Place the shock upside down and angle it so that the lowest point is the corner of the 180? elbow that has an allen-head bolt recessed into it. Add a small amount of shock fluid to the main shock body and then tilt the shock so the shock fluid will drain into the reservoir. Repeat this process until the reservoir is filled with shock fluid and all of the air has escaped. It might be necessary to fill the shock body with a volume of fluid, replace the shock shaft & seal housing, and then rotate the shock body so that all of the air escapes from the reservoir and bleeds into the main shock body. Then remove the shock shaft/piston again, and set the final fluid height.
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Clamp the shock upside down in a vice again. Fill the shock body with shock fluid, up to about 1’ below the groove for the circlip that holds the seal carrier. Wrap a shop rag around the shock body to catch shock fluid overflow. Slowly re-install the shock shaft into the shock body. A small amount of shock fluid should spill over, insuring that no air is trapped in the shock body. Slide the shaft in until the piston and shaft spacer are both fully submerged in shock fluid. Be sure to go slowly, you may need to twist the shaft to ease it in. Depress the seal carrier until you can see the circlip groove, re-insert the circlip and gently pull upward on the shaft to fully seat the circlip. Slide the Dust wiper down the shaft and secure it snugly with the three allen-head bolts. Cycle the shock from full extension all the way to full compression. Verify that you are getting the proper amount of travel and also check for air pockets (if there is any air in the shock you will need to add more shock fluid). If there is too much shock fluid (hydraulic lock) you will need to remove some shock fluid and reset the floating piston depth in the reservoir.
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Re-install the shocks and hardware in reverse order of removal and then pressurize the chamber with nitrogen, via the Schrader valve, to 200psi. If you don’t have nitrogen on hand you can use a high-pressure bicycle shock pump to charge the shock with air so that you can drive to a shop to have the shocks properly charged with nitrogen. Note: Driving the vehicle without pressurizing the reservoirs can damage the piston/reservoir.
Rebuilding and custom-valving our shocks has made a WORLD of difference in the performance, handling and ride quality of the Trails Less Traveled Tacoma. We haven’t had an opportunity to really work-out the suspension hard since these changes were made, but can already tell that the box-stock valving wasn’t giving us the dampening we needed.
This Article was originally published on Off-Road.com May 2004
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