Sway-A-Way 2.0x4
Published by Trails Less Traveled on May 10th, 2004
INTRODUCTION
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After having Deaver custom-tune our leaf springs, and re-valving our RaceRunner shocks, we were really happy with the performance of our rear suspension. But then we added RaceRunner bypass shocks up front, we wanted to balance out the damping by adding a pair of progressive bump-stops to the rear of the Trails Less Traveled Tacoma.
Swayaway Racerunner bump-stops perform the same basic duty as standard mechanical bump-stops, but they do a much better job. The hydraulic bump-stops have 4” of travel and are charged with 200psi of nitrogen to slowly halt the upward motion of the wheels and related drive-train components. They offer a much more progressive feel, as opposed to suddenly bottoming against a hard rubber bump-stop. A properly designed suspension with hydraulic bumps can be tuned to feel virtually bottomless.
BLUEPRINTING
Deciding where and how to mount the hydraulic bump-stops was a process of elimination. Mounting the bump-stops on the inside of the frame-rails was not an option. Aside from interfering with the shocks, we were concerned that if the shocks are mounted closer to the tires than the bump-stops, that the bump-stops could not be positioned to effectively control vertical and articulated compression travel. The bump-stops would either be mounted too low (allowing full articulation but limiting vertical compression), or too high (allowing for full vertical compression but causing the shocks to bottom-out on articulated compression).
On a live-axle suspension, the bump-stops must be mounted closer to the tires than the shocks. But we couldn’t mount them outboard of the frame-rails because they could have come into contact with the tires on articulated compression travel. Even if we could have positioned them on the outside of the frame-rails (by installing a wider rear axle, etc), we would have been concerned about the leverage twisting the frame-rails. Also, the bump-stops will start to limit articulated travel if they are mounted too far outside of the shocks.
Ideally, our bump-stops would be located in-line with the rear shocks (when viewed from the front/back). They could be positioned to effectively control vertical and articulated compression travel without allowing the shock to bottom-out. But considering the real-world limitations of our chassis layout, we decided that the ideal location for our application was right in-line with the frame-rails, outside of the shocks. Rock Star Trux, in San Jose CA, had already strengthened the frame by fully boxing/plating the inner channel, so we weren’t too concerned about potential strength/structural issues associated with interrupting the frame-rails. We planned to gusset the junction where the bump-stops pierced the frame-rail to further strengthen that high-stress area.
In order to determine the final placement of the bump-stops, we partially disassembled the rear leaf springs so that we could easily cycle the suspension. It’s important to locate the bump-stops on the same plane as the axle path in order to minimize scrub. Scrub could simply be defined as any force that would side-load the bump-stop or cause it to slide along a surface on a different plane than it’s stroke. Scrub is almost impossible to eliminate entirely, but excessive amounts will reduce the effectiveness of a bump-stop, and cause binding and/or wear on the bushings/internals.
We focused on the axle-path at the last part of the compression stroke (from the point that the axle would come into contact with the bump-stop through full compression) and took some measurements to determine the angle that would minimize scrub. We also positioned the contact patch on the center of the axle housing, and paid consideration to the material that would have to be added to the axle-housing to strengthen that area and keep it from collapsing.
INSTALLATION
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We laid out the measurements on the frame-rail and then began by carefully removing material from the outside frame-rail with a cut-off wheel. We had to cut the outside frame-rail because the frame-rail wasn’t quite wide enough to accommodate the pre-fabricated bump-stop mounting canisters that we bought from Kartek. We also needed to remove the stock LSPV mounting bracket from the driver’s side frame-rail because we didn’t cut it out when we plated the inner frame-rail.
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We then used a hole-saw to pierce the upper and lower side of the frame-rail; making a perfect slot to slide the Kartek bump-stop mounting canisters into.
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Here is the Kartek mounting canister mocked up before being welded in place. The surrounding paint has been ground away so we can further reinforce the area by welding in gussets. Notice that it is recessed up into the frame-rail as high as possible, so as not to limit compression travel.
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After fully welding and gusseting the mounting cans, we sprayed on a few coats of paint, bolted in the bump-stops and pressurized them with 200psi of nitrogen.
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Here is what the Sway-A-Way Racerunner hydraulic bump-stops look like after the completed installation. Before we can head out to test them, we need to fabricate a new type of leaf-spring U-bolt mounting plate that will provide a flat contact pad for the bump-stops to strike on compression. As things are now, the outer leaf-spring U-bolt would side-load the bump-stop on articulated compression travel and cause severe damage. Look for an update as we work out a solution.
This Article was originally published on Off-Road.com May 2004
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