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JKS Adjustable Control Arms

Posted in How To on October 30, 2006
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Photographers: Michael SladeDavid Conover

Control arm selection can be a daunting task for any coil-sprung Jeep owner as the number of choices available today is overwhelming. The fact that so many control arms are nearly identical in appearance only makes the decision more confusing. In many cases, we simply cannot make an informed choice without examining the product's internal design and construction.

"So just how can I see inside a control arm?" you ask?

We're going to make it easy for you with an exclusive look at the JKS Adjustable Control Arm - from the inside out!

The importance of a properly engineered control arm is often overlooked when shopping for a new suspension system. Although the correct spring and shock specifications are paramount to the performance of your newly suspended Jeep, an inferior set of control arms can leave you with feelings of lift-kit remorse. To better understand why control arm design is such an important factor, we must look at the role this part plays in the Jeep suspension system.

Control Arm Function
A combination of upper and lower control arms links the axlehousing to the chassis using bushings at each end to accommodate suspension movement. As the suspension compresses and extends, the control arms literally control the position of the axle relative to the chassis. At factory ride height, the operating angles of the control arms remain relatively parallel with the ground; however, as ride height increases, so do the operating angles. This exposes the control arms to much greater forces because they are no longer able to deflect impacts as efficiently.

The decrease in deflection efficiency is more prevalent on the front suspension. With the control arms mounted to the chassis behind the axle, they actually force the tires into an obstacle before deflecting the impact to the springs and shocks. This can transfer a considerable amount of noise and vibration into the vehicle cabin. The problem is most noticeable on Jeep models that have a unibody chassis, since they don't benefit from an additional set of rubber isolator mounts between the body and chassis.

Overview of Adjustable Control Arms
If you own a coil-suspended Jeep, you may already be familiar with the advantages of adjustable control arms. For instance, camber and pinion angles can be changed by simply adjusting the upper or lower control arm lengths independently. Adjust the upper and lower arms together and you can move the entire axle assembly fore and aft - this is particularly advantageous on vehicles with large tires and limited space for them to move within the wheel openings. Some adjustable control arms even rotate during normal operation to accommodate suspension articulation. It is important to note that the methods by which these functions are achieved can vary considerably.

Description Of Jks Control Arms
Adjustment Threads
Threaded adjustable control arms are not uncommon in the marketplace, but JKS has taken a unique approach to designing its control arms. For starters, 18-tpi (threads per inch) adjustment threads were utilized instead of the mere 5-tpi threads found on most other control arms. The fine thread pitch is actually stronger due to better thread engagement and a larger cross section since less material is removed during the thread forming process.

In addition to the overall increase in strength, the fine thread pitch also allows greater precision when adjusting the control arm length. Each turn of the rotating end fine-tunes the length a minute 1/16 inch. With over 3 inches of adjustment available, the working length of each JKS control arm can be increased, decreased, or left exactly the same as the OE suspension arm.

The free-rotating JKS design doesn't require a jam nut either - jam nuts have been known to loosen on the trail or seize up when you want to make an adjustment. Instead, each end twists with the respective axle and chassis mounts for unrestricted suspension articulation. JKS also incorporates a special internal stop mechanism that ensures full thread engagement at all times. Simply put, the control arm can't be unthreaded far enough to compromise strength and safety.

Internal Support Bearing
Another unique feature of the JKS control arm is the internal support bearing. This slippery brass bearing is a vital part of the design that counteracts any lateral loads, ensuring the inner rod remains concentric with the outer body. Without the bearing, the adjustment threads would be vulnerable to excessive leverage, which could eventually lead to deformation. According to JKS, thread deformation is the primary reason that other control arms can wear out prematurely and produce noise that transmits into the vehicle cabin.

Lubrication System
The reliability of the JKS design requires a lubrication system that can evenly distribute grease to all internal contact surfaces. Although JKS prelubricates all of its arms before they are packaged and shipped, it will be necessary for the user to add grease at regular maintenance intervals. Lubricant is pumped into the external grease zerk which aligns with an internal channel that is machined into the adjustment threads. The channel also ensures distribution of the grease to the internal support bearing. A spring-loaded seal keeps the lubricant where it belongs while preventing moisture and contaminants from entering the control arm.

Whereas most aftermarket control arms are attached to the vehicle with either polyurethane bushings or spherical rod ends, JKS chooses good old-fashioned rubber. This decision is considered controversial by those who prefer synthetic bushing materials for their more resilient qualities; however, JKS only uses the high-quality, vulcanized rubber bushings that are found on the original equipment suspension arms. These genuine OE parts are far superior to the lower-grade alternatives commonly sold as replacements.

The most obvious benefit of using rubber bushings is immediately noticeable inside the vehicle. Unlike denser materials, rubber bushings do an extremely effective job of isolating noise and vibration that would otherwise resonate into the vehicle cabin. Almost anyone who has replaced the factory suspension arms with aftermarket components can likely recall the immediate effect from the driver's seat.

Another important advantage of using rubber bushings involves their impact on the related mounting brackets. Although rarely mentioned, firm polyurethane bushings and rigid control arms can actually tear the factory mounting brackets away from the chassis or axle when exposed to severe conditions. On the other hand, high-quality rubber bushings are able to absorb damaging impacts and lateral forces instead of resisting them. Needless to say, a broken control arm bracket on the trail is not a situation you want to experience firsthand.

Materials and Finish
One can't help being immediately impressed when holding a JKS control arm in one's hand for the first time. While surprisingly simple in appearance on the outside, the unit's weight is the first suggestion that there is more than initially meets the eye. The heavy-gauge steel body is finished in rich black powdercoat, and the rotating 1.25-inch-diameter, solid steel rod has received a protective zinc plating. The rubber bushings at each end are easily identified as original equipment parts.

JKS informed us that it keeps a supply of new bushings on hand in the unlikely event of the originals wearing out, but the company assured us that this circumstance is extremely rare. JKS was also proud to announce that it has never had a control arm fail or wear out since it introduced the product more than six years ago. Now that we've had a firsthand look from the inside out, we believe 'em!

Extended-Length Control Arms
Many suspension manufacturers now offer control arms that are much longer than normal as a means of compensating for the increased operating angles. Although they can reduce the operating angles considerably, they no longer utilize the factory chassis mounts and some even require custom fabrication to install. Due to the additional factors involved, we won't go into greater detail on extended-length arms in this article; however, we will mention that you may find the benefits of extended-length control arms to be well worth the effort and expense if your Jeep is lifted or used to the extreme.

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