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We Build A Lightweight Fuel-Efficient Daily Driver/Rockcrawler Chevy Tracker: Part 2

Posted in Project Vehicles on June 1, 2015
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We knew from the start that we were going to ditch the independent front suspension on our Tracker project for a custom linked suspension front and rear. While that decision was easy, determining exactly what would fit and meet our needs for extreme rockcrawling while remaining street legal was a bigger challenge. And as with many projects, we fell a little behind schedule. This month we will talk about the theory behind the suspension configuration and components we chose, and next month we will go into more detail on how the final product was install on the Tracker.

Front Suspension
Front solid-axle link suspensions can consist of a three-link, a four-link, or radius arms, which in that order decrease from more to less articulation. All of these suspension designs utilize a track bar (Panhard bar) to locate the axle laterally. The bar should be parallel to the drag link in order to minimize bumpsteer. A triangulated front suspension would require full hydraulic steering or a complicated bell crank steering system to avoid massive bumpsteer as the suspension articulates. Neither steering system was considered practical for our lightweight, street-legal Tracker.

Radius arms and four-link suspensions have been used on the front of everything from Early Broncos to JK Wranglers. They provide good stability and are consistent from side to side (react the same regardless of whether the driver side or the passenger side is compressing). They also tend to bind during articulation, which can be useful since it acts as roll resistance (the same effect as a sway bar), but binding limits articulation.

We chose a three-link front suspension for our Tracker with two lower links to position the axle, one upper link to prevent the axle from rotating, and a track bar to locate the axle laterally. The distance between the upper and lower links must be great enough to prevent the axle from rotating when power is applied, but an overly tall upper link mount will limit uptravel before contacting the frame and can swing into the frame or oil pan under articulation depending on location. With only one upper link, binding is greatly reduced when compared to a four-link suspension, but it must be built strong enough to control axle twist, and we anticipate adding a sway bar to add stability on the street. The track bar will be positioned parallel to the steering drag link to minimize bumpsteer and ideally flat at ride height for an improved roll center.

On the front of the Tracker, the new Diamond axle needed to be positioned far enough forward to clear the sump on the oil pan at full compression. While this had the added benefit of stretching the wheelbase and improving the approach angle, it made packaging the track bar and drag link more challenging. On the front of the Tracker, the new Diamond axle needed to be positioned far enough forward to clear the sump on the oil pan at full compression. While this had the added benefit of stretching the wheelbase and improving the approach angle, it made packaging the track bar and drag link more challenging.
Haines built a crossmember out of 13⁄4x0.156-wall tubing to mount the front suspension links. Since the crossmember is under the transmission, tube clamps from Trail-Gear were added to service the drivetrain. Haines built a crossmember out of 13⁄4x0.156-wall tubing to mount the front suspension links. Since the crossmember is under the transmission, tube clamps from Trail-Gear were added to service the drivetrain.
Jesse Haines measured the centerline of the axle to make certain that it was centered under the chassis. Mounting the lower links to the axle means finding a balance between fitment on the axlehousing and a separation wide enough for stability yet compact enough to allow the tire to turn to full lock without contacting the link. Jesse Haines measured the centerline of the axle to make certain that it was centered under the chassis. Mounting the lower links to the axle means finding a balance between fitment on the axlehousing and a separation wide enough for stability yet compact enough to allow the tire to turn to full lock without contacting the link.
Rod End Supply makes rod ends in a number of sizes and materials for everything from carburetor linkages to Trophy Truck suspensions. We chose chromoly steel XM rod ends that are self-lubricating with a Nylafiber matrix race. While they more economical rod ends, Rod End Supply’s Bob Douglas stated that XM rod ends are a great long-term value since they stay tight for so much longer than conventional rod ends. Rod End Supply makes rod ends in a number of sizes and materials for everything from carburetor linkages to Trophy Truck suspensions. We chose chromoly steel XM rod ends that are self-lubricating with a Nylafiber matrix race. While they more economical rod ends, Rod End Supply’s Bob Douglas stated that XM rod ends are a great long-term value since they stay tight for so much longer than conventional rod ends.
Misalignment spacers allow more angularity out of a rod end at the expense of the hardware size. We will be using misalignment spacers from Rod End Supply on our drag link, but suspension links will not require them due to the orientation of the rod ends. Misalignment spacers allow more angularity out of a rod end at the expense of the hardware size. We will be using misalignment spacers from Rod End Supply on our drag link, but suspension links will not require them due to the orientation of the rod ends.
Weld washers don’t offer as much angularity as misalignment spacers, but they also do not require a smaller fastener to be used. Haines recommended running weld washers on all the control arm brackets to add a small degree of angularity. The larger benefit though is the ability to build thinner, and thus lighter, brackets without concern of the holes becoming egg-shaped after hard use off-road. Weld washers don’t offer as much angularity as misalignment spacers, but they also do not require a smaller fastener to be used. Haines recommended running weld washers on all the control arm brackets to add a small degree of angularity. The larger benefit though is the ability to build thinner, and thus lighter, brackets without concern of the holes becoming egg-shaped after hard use off-road.

Rear Suspension
The rear suspension does not have to share space with steering components or concerns about tire clearance at full lock, simplifying the process. Common rear suspensions consist of four links with a track bar, such as is found on the rear of JK Wranglers, and three links or triangulated four links that eliminate the requirement of a track bar. Like the front suspension, using a four-link with a track bar allows for abundant vertical wheel travel but can cause binding when the suspension articulates. This is why many Jeep owners convert to a triangulated rear suspension, whereas you do not have the bumpsteer issues that prevent this suspension configuration from typically being used on the front of 4x4s.

The issue with a triangulated four-link is packaging of the upper links, particularly with a vehicle like our Tracker, where we are trying to keep the ride height as low as possible and still allow for 5 inches of uptravel. Nothing can be in the way of the upper links as the suspension articulates, making it difficult to package a fuel tank or exhaust components. For these reasons, fabricator Jessie Haines recommended running a three-link suspension with a track bar mounted in the opposite orientation from the front suspension (frame side of the bracket on the passenger side, and axle side of the bracket on the driver side). This allows us to move the axle rearward to lengthen the wheelbase and improve our departure angle without concerns about the upper links contacting the chassis or the body on full compression, and it allows plenty of space for our exhaust system.

Now that we have decided on the right suspension geometry for our application, it is time to install our ADS air shocks, Trail-Gear steering components, and heat-treated chromoly links with Rod End Supply chromoly rod ends. Check back next time to see how it all turned out.

Misalignment spacers, jam nuts, and weld-in bungs are all available from Rod End Supply. If you know the length of control arms you need, you can even purchase completely welded links in DOM or chromoly from Rod End Supply. Misalignment spacers, jam nuts, and weld-in bungs are all available from Rod End Supply. If you know the length of control arms you need, you can even purchase completely welded links in DOM or chromoly from Rod End Supply.
Mounting the lower links on the centerline of the axletube maximizes ground clearance and also minimizes the angle of the links at ride height. Haines made the links 32 inches long, long enough to provide plenty of articulation and minimize angle change as the suspension cycles but still be short enough that they do not hang down excessively and impede progress when the front tire rolls over a boulder. Mounting the lower links on the centerline of the axletube maximizes ground clearance and also minimizes the angle of the links at ride height. Haines made the links 32 inches long, long enough to provide plenty of articulation and minimize angle change as the suspension cycles but still be short enough that they do not hang down excessively and impede progress when the front tire rolls over a boulder.
An FJ60 steering box was sourced from Trail-Gear. This Toyota box is much more robust than anything Suzuki ever offered, and unlike a more common Toyota pickup steering box, the pitman arm faces forward on the FJ60 box. This positions the drag link forward for increased clearance with the suspension components. An FJ60 steering box was sourced from Trail-Gear. This Toyota box is much more robust than anything Suzuki ever offered, and unlike a more common Toyota pickup steering box, the pitman arm faces forward on the FJ60 box. This positions the drag link forward for increased clearance with the suspension components.
The front suspension on Haines’ previous flatfender buggy used a triangulated four-link with a traditional steering box to conform with rules for the class it was raced in. The steering box was mounted on the firewall and used a bellcrank system. This maximized articulation and minimized bumpsteer, but it was heavier and more complex than we wanted on our Tracker. The front suspension on Haines’ previous flatfender buggy used a triangulated four-link with a traditional steering box to conform with rules for the class it was raced in. The steering box was mounted on the firewall and used a bellcrank system. This maximized articulation and minimized bumpsteer, but it was heavier and more complex than we wanted on our Tracker.
Haines’ rockcrawling buggy uses an offset rear differential and a three-link rear suspension with a track bar. We plan to mimic this setup on our Tracker. Note how much longer the track bar bracket is than a typical Jeep suspension. This increases the roll center of the vehicle, providing stability in off-camber situations. Haines’ rockcrawling buggy uses an offset rear differential and a three-link rear suspension with a track bar. We plan to mimic this setup on our Tracker. Note how much longer the track bar bracket is than a typical Jeep suspension. This increases the roll center of the vehicle, providing stability in off-camber situations.
Another popular rear suspension option is a triangulated four-link. By triangulating the upper suspension links, they not only prevent the axle from rotating but also locate it from side to side. The only reason we chose not to run this form of suspension on our Tracker was for packaging concerns with the low ride height of the vehicle. Another popular rear suspension option is a triangulated four-link. By triangulating the upper suspension links, they not only prevent the axle from rotating but also locate it from side to side. The only reason we chose not to run this form of suspension on our Tracker was for packaging concerns with the low ride height of the vehicle.
Weight is an important factor for this project. The 21⁄2-inch-diameter, 12-inch-travel ADS air shocks we used only weigh 14 pounds each. Comparable coilovers would weigh over 20 pounds at each corner. Some of that weight savings will be offset by the addition of a sway bar, since air shocks offer very little roll resistance. Weight is an important factor for this project. The 21⁄2-inch-diameter, 12-inch-travel ADS air shocks we used only weigh 14 pounds each. Comparable coilovers would weigh over 20 pounds at each corner. Some of that weight savings will be offset by the addition of a sway bar, since air shocks offer very little roll resistance.

Air Shocks or Coilovers?
ADS makes all kinds of shocks, from 2-inch-diameter coilovers to 5-inch-diameter bypass shocks for Trophy Trucks and everything in between, including the 21⁄2-inch-diameter air shocks that we chose for our Tracker. The most common advantages attributed to air shocks are their low cost and easy packaging compared to coilover shocks. The downside is that air shocks offer less tuning since the ride height and spring rate are both a function of the nitrogen charge in the shock.

Sources

Trail-Gear
Fresno, CA 93727
559-252-4950
www.trail-gear.com
Rod End Supply
Olathe, KS 66051
800-284-2902
http://www.rodendsupply.com
Jesse Haines Fabrication
http://www.facebook.com/jesse.haines.12
ADS Shocks
520-748-0005
http://www.adsshocks.com

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