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The Rise & Fall of "Project ZJ"

Publish date: Oct 1, 1998
By: Tony Curless
Source: Jeep at Off-Road.com

The majority of Grand Cherokee owners chose to purchase their vehicle because it was a well-rounded, class-leading sport utility vehicle that was a pleasure to drive. Little thought, if any, was given to the Jeep?s ability to conquer extreme four wheel drive trails. But after a few off-road excursions, when the factory tire size and vehicle?s ground clearance prove inadequate for real off-road use, the typical Grand Cherokee owner yearns for more. Soon a mild suspension lift and larger than stock tires find their way onto the vehicle, and suddenly the game begins.

The new suspension and tire combo works well for awhile, but it doesn?t take long for the driver to find the Jeep?s limitations once again. Off with the swaybars, and in with a traction control device. Now we?re having some fun. Does this sound familiar to you? Well, if you?re reading the pages of Grand Cherokee UnLimited, it?s likely that you?ve played this game before. And if you haven?t, be prepared for one of the most addictive hobbies you?ll ever encounter.

As with other motorsports, the hobby of four wheeling is not without risk. You risk damaging your vehicle, and you risk injuring yourself and your passengers. But without a certain amount of risk, the sport would lose it?s excitement. The thrill of overcoming nature?s obstacles, especially those that were never meant to be attempted in a luxury sport utility vehicle, is extremely rewarding. This thrill and excitement is the fuel for our four wheeling fire.

Several years ago, I was drawn into this hobby, and I?ve been addicted ever since. I started with a ?93 Grand Cherokee Limited, which has been through some drastic changes in the time that I owned the vehicle. First, a Pro Comp suspension and 31" BFG A/T tires were mounted to the Jeep, followed by a Warn winch combo shortly thereafter. The front swaybar received a set of JKS quick disconnects, and instantly the Jeep was taking me places that were impossible in stock form. Behold?the game had begun, and I was hooked.

As Grand Cherokee owners, we are probably more sensitive to vehicle damage than those who own other four wheel drive vehicles. Therefore, it?s important to take steps to prevent damage that is likely to happen on the trail sooner or later?if you?re not prepared, expect the damage to occur sooner. Probably the first, and possibly the most important modification you can make to protect your ZJ?s sheetmetal, is to invest in some quality rocker panel protection. No matter how high your Grand Cherokee is lifted, rocker panel damage is sure to happen eventually. Investing in a set of rocker guards now will save you a lot of money and frustration down the road. Unfortunately, I learned this the hard way. During a trip to Moab, Utah, my passenger side rocker panel came in contact with a rock, resulting in a three-foot scrape on the rocker panel, and a lot of green paint on the rock. This incident convinced me to order a set of quality rocker panel guards and a taller suspension system.

Soon after, my Jeep was riding on a 4.5" Off Road General Store suspension lift and 33" BFG M/T tires. A set of Off Road General Store "Super Nerfs" were on order, and would be delivered in 4-6 weeks. Now that the rocker panels had an extra three inches of ground clearance, I felt confident that they would stay clear of any potential damage caused by obstacles on the trail. WRONG! The ORGS suspension lift and larger tires worked so well off-road that I had the confidence to tackle more difficult terrain. It didn?t take long before I had a matching scrape on the driver side rocker panel. When the ORGS "Super Nerfs" arrived, both rocker panels had extensive damage, which would have been prevented if I had ordered them when I first began venturing off-road.

With the "Super Nerfs" installed, my confidence level was boosted once again. Dropping off of steep ledges was no longer a concern, as the nerf bars protected the rocker panels in virtually any situation. With time and use, I found the "Super Nerfs" to be one of the most versatile and effective modifications I had installed on the Grand Cherokee. Had I installed the nerf bars before the damage, I?m confident that the rocker panels would have remained scratch free for as long as I owned the Jeep.

Like the Grand Cherokee?s rocker panels, the front and rear bumpers are also prone to damage on the trail. In stock form, the vehicle?s approach and departure angles leave a lot to be desired, when compared to the ZJ?s short-wheelbased siblings. Unfortunately, Grand Cherokee owners are somewhat limited when the time comes to replace the factory bumpers, as the aftermarket selection has little to offer. The ARB Bull Bar seemed to be the most logical option for the front of the vehicle. Accommodations for a winch, auxiliary lights, and vehicle recovery points are all integrated into it?s design. In addition, ground clearance and approach angle are dramatically improved. Overall, the Bull Bar proved to be extremely functional while adding an aggressive demeanor to the Jeep.

For the rear of the vehicle, I chose Tomken Machine?s Protec bumper with a swing-away tire carrier. Tomken offered the only rear bumper available for the Grand Cherokee at the time, so the decision was easy. The swing-away tire carrier can be used to carry a Hi-Lift Jack and Gerry can, when the optional mounting brackets are installed. Overall, the Tomken rear bumper is extremely stout, and well made. It has protected the Jeep?s posterior on several occasions, where the factory bumper would have been ripped to shreds. However, the mounting system is questionable for those interested in carrying a 33" spare tire on the swing-away carrier. The Tomken bumper is not as attractive as the ARB Bull Bar, but when combined with the swing away tire carrier, the bumper looks good on the ZJ.

Even though the Jeep was now set up to tackle nearly any obstacle I threw it?s way, I still desired more?more traction, more lift, more suspension travel, and more thrills! Crippled by open differentials in the stock axles from the factory, the Jeep struggled when the ORGS suspension wasn?t able to keep all four wheels on the ground. The factory drivetrain only provided two wheel drive when the Jeep encountered terrain with little, or no, traction. In addition, the full-time "Quadra Trac" transfer case only exaggerated the situation, since the early version of the NP249 didn?t lock the driveshafts together when engaged in 4 Lo. To increase traction at the wheels, ARB Air Lockers were installed in both axles, along with 4.56 ring & pinion gears to offset the larger tires. The addition of locking differentials made an incredible difference. They provided both wheels on each axle with 100% of the driving force when activated via a dash mounted switch. Many of the poor off-road characteristics exhibited by the non-locking transfer case were greatly improved when the front and rear Air Lockers were engaged.

Despite the instant traction increase caused by the ARB locking differentials, the full-time transfer case was still detrimental to off-road performance. On high traction terrain, such as the slickrock trails in Moab, the NP249 t-case would distribute the majority of the engine?s power to either the front or rear axle when the vehicle encountered steep or uneven surfaces, acting very much like an open differential. To remedy the situation, the NP249 transfer case was replaced with a part-time NP231 unit from a ?97 Jeep Wrangler TJ. The NP231 t-case was chosen for many reasons, including strength, parts availability, and ease of installation. It allows the vehicle to be driven in two wheel drive, and when four wheel drive is engaged, the driveshafts are locked together, resulting in a substantial increase in traction. To complement the new transfer case, a JB Conversions slip yoke eliminator kit was installed, which replaces the smaller output shaft with a much stronger shaft out of an NP241, commonly used in full-size Chevy trucks.

With the 4.5" lift, 33" tires, and drivetrain upgrades, the Jeep remained agile on the pavement. The vehicle required a bit more attention to keep the wheels between the yellow lines, but remained predictable when evasive driving was required. Steering was almost as responsive as stock, with the front swaybar connected. However, care should be taken when the front swaybar is disconnected, as excessive body lean and wandering was experienced.

Looking for even more off-road performance, a custom 6" suspension lift was designed for the ZJ, consisting of parts from manufacturers such as Off Road General Store, Currie Enterprises, Rancho, and National Spring. Currie?s new articulating control arms were used to allow for extreme wheel travel without placing stress on the uni-body. A set of custom National coils were made to lift the front of the Jeep, while Rancho coils provided the lift in the rear. Lifting a Grand Cherokee to such an extreme height requires careful attention to the control arms and track bars, as well as steering and drivetrain components. A job such as this is best left to a skilled professional, as safety can be easily compromised by the inexperienced.

The custom suspension lift worked incredibly well on the trail, and wheel travel improved dramatically. When testing wheel travel on a 20-degree ramp, the Jeep was able to squeeze just over 1,000 points (RTI) out of the revamped suspension. However, the increase in lift height does cause a few handling quirks that cannot be ignored. Anytime you lift a vehicle to extreme levels, especially one suspended by coil springs, extra care must be taken to result in safe on-road characteristics. In the Grand Cherokee?s case, the control arms and track bars are placed at severe angles.

The control arms are mounted to the vehicle?s sub-frame and axles. Their purpose is to locate the axle fore and aft, but unlike a leaf spring design, they don?t offer any lateral stability. Each axle is connected to the sub-frame with four control arms?two upper arms, and two lower arms. Lateral stability is provided by the track bars, which limit the axles? side-to-side movement. A single track bar is used for each axle, and like the control arms, the track bars attach to both the axle and sub-frame.

Optimally, these components should be nearly parallel to the ground, as they are on a stock vehicle. However, when adding a suspension lift to your ZJ, the axles are located farther away from the sub-frame, causing the severe angles. This, in turn, affects the path that each wheel follows during suspension compression and droop. Jeep engineers designed the Grand Cherokee?s "Quadra Coil" suspension to move the axle in a specific arc when suspension travel is experienced. Changing this arc negatively affects the way the vehicle will respond to uneven road conditions. Since re-designing the entire "Quadra Coil" suspension system is an extremely complicated process, owners of modified Grand Cherokees have been forced to live with the consequences.

Suspension lifts up to 3" cause very little changes in the control arm/track bar angles. Such a modest increase in lift height will rarely cause any negative handling characteristics. However, the amount of problems that are experienced are related directly to the amount of suspension lift added after this point. For Grand Cherokees that spend the majority of time on the road, it is generally recommended to refrain from suspension lifts exceeding 4.5". This seems to be the ZJ?s "magic number" when it comes to maintaining acceptable on-road handling characteristics.

After driving the Jeep for a few months with the custom 6" suspension lift, I felt confident that I could control the vehicle through just about any situation that should arise. Although the vehicle handled and responded much different than stock, I was comfortable using the Jeep as my daily driver. Getting used to the new driving characteristics took some time, but eventually I became accustomed. With time, I once again felt united with the vehicle. A feeling of invincibility overwhelmed me every time I slipped behind the wheel. Nothing could come between me and my destination, until?

September 5, 1998 -
While traveling on a county road just minutes from my house, I encountered an experience I will never forget. I was on the way home that night, when I drove through a small rut in the middle of the road and lost control of the Jeep. I was only traveling about 30 mph, but the rut caused the rear end to slide sideways, pointing the vehicle towards a ravine. I immediately counter-steered and applied the brakes, causing the Jeep to spin the other direction. Now I was facing an embankment on the right side of the road, and the Jeep continued to slide sideways. The passenger side front wheel began to climb the dirt embankment, shifting the weight of the vehicle down hill. Gravity took over at this point, and pulled the Jeep onto it?s left side, and finally onto the roof. With all four wheels reaching for the stars, the vehicle came to a stop. Luckily, my passenger and I were both wearing our seat belts, so no injuries were sustained. However, the Jeep was damaged beyond repair, and my feeling of invincibility was suddenly shattered.

What?s the moral of this story, you ask? When adding an extreme suspension lift to your Grand Cherokee, it may be necessary to change your driving habits. Drivers of lifted vehicles need to be more attentive and alert to his or her surroundings. Vehicles with modified suspensions handle differently than stock, and it?s your responsibility to alter your driving style in order to maintain control of your vehicle. No matter how comfortable you feel behind the wheel, accidents can happen at any time, and the consequences can be fatal. When driving a lifted Grand Cherokee, give yourself more time to react to situations by lowering the vehicle?s speed and increasing awareness. Those who live in highly populated areas need to take extra precaution when driving in traffic, as other drivers are unpredictable. Most accidents can be avoided, and preparing yourself for the unexpected is the best form of insurance.