Most 4x4 owners equate handling and articulation with hard parts: namely springs, track bars, and control arms. We tend to overlook bushings.
OE suspension and steering components normally have rubber bushings. Cost-effective, these score high in NVH (noise, vibration, harshness) tests. Rubber’s main compromise is it wears out faster than firmer materials. Sunlight, ozone, grease, and road grime accelerate its demise. Further, bonded rubber bushings can be a pain to change.
Polyurethane bushings aren’t always the cheapest replacements, but they offer a few advantages over rubber, mainly durability. Poly bushings are usually firmer than rubber, so they’re less susceptible to tearing and shearing. Chemical-resistant polyurethane doesn’t degrade from UV rays, oil, grease, and other contaminants.
Further, firmer polyurethane usually yields stiffer handling. (Hardness in polymers and rubber is measured on a durometer, so firmness difference can be quantified when OE specs are available.) RTI ramp-champs and long-travel legends might want to stick with rubber for ultimate flexibility, knowing that service intervals could be shorter. However, many lifted 4x4s, particularly ones that tow, can benefit from a poly rebush.
Energy Suspension recently released a master poly bushing kit for ’03-’08 Dodge 4x4 HDs. These Rams have a reputation for dodgy handling, particularly when running larger-than-stock tires. Typical prescriptions include aftermarket dual steering stabilizers, heavier-duty front track bars, and steering-box frame braces. However, replacing tired rubber bushings with polyurethane might actually be a better bang-for-the-buck starting point.
The engineering challenge is finding the optimal durometer measurement for each part. For example, control-arm bushings have to absorb both lateral and fore/aft forces. Energy Suspension engineers address this by making the side bushings softer than the center pieces. Performance characteristics can also vary within the same hardness: Two Energy Suspension bushings with “hard” 90 durometer readings might have different Hyper-Flex poly recipes depending on whether their functions are primarily torsional or tensile.
These photos show highlights of Energy Suspension engineers installing the new kit on an ’03 Cummins that had 177,000 miles on its stock bushings. This vehicle routinely tows a fifth-wheel, so it was a prime candidate for the upgrade. The hardest part of the job is removing the stock bushings from the arms and springs. Some tools that might be helpful for a DIY job:
• A vise or, preferably, a hydraulic arbor press
• Impact sockets
• Large channel locks
• A torch (torching was not used on this install)
This job took the Energy Suspension pros the better parts of a day. (Professional wheel alignment might be necessary for some vehicles.) Most of that time was spent pressing out the worn OE bushings. But at the end of the day these new poly parts just might outlast the rest of the truck.