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Note: The Jeep Configuration page has much of the same information here collected from a variety of sources. There are some difference of opinions in the jeeping community which are discussed there. e.g. many don't like differential skid plates because they reduce clearance.


The following is from an article in the Lousiana 4x4 Club
Over The Hill Newsletter Vol. 9, Number 8, Aug. 2003

Why Modify Your Jeep

Safety and Vehicle Protection | Vehicle Recovery | The Law of Unintended Consequence | Traction | Ground Clearance

The Wrangler TJ, in any configuration, is an extremely capable off road vehicle right off the show room floor. In fact all Jeeps sold with 4-wheel drive are very capable off road. There is very little, if any thing, which needs to be done to the Jeep for the driver to be able to enjoy the off road experience.

If the Jeep did not come with tow hooks front and rear, then these should be purchased and installed before venturing off road. Tow hooks for the front of the Jeep are inexpensive and easy to install. A viable option to rear tow hooks is a trailer hitch, but is more expensive. Another thing to purchase before going off road is a tow strap. In selecting a tow strap, look for one without metal hooks, that is rated at least 20,000 lbs. It cannot be stressed enough the importance of not having metal hooks, as a strap with hooks is extremely dangerous.

Off road driving is all about driving skill, ground clearance and traction. Of the three driving skill is the most important, and the novice off roader should concentrate on improving his/her driving skill before making any major modifications to his/her Jeep.

The basic reasons to modify your Jeep are:

1. Safety and Vehicle Protection

Safety items would include simple things like a fire extinguisher and a first aid kit. This would also include such modifications as adding a full roll cage or 5 point harness seat belts. (The roll bars that come with a TJ are quite strong and is adequate for most trails.)

Modifications made to protect the vehicle include:

Stronger bumpers - The stock bumpers, particularly those plastic end caps are probably the biggest weakness of the TJ. If you do much off roading it won't be long before those end caps are ripped off. It probably won't be much longer before the bumper gets bent. Most off roaders replace the stock bumpers with stronger after market bumpers designed for the riggers of off road.

Spare tire carrier - If larger heavier tires are put on the Jeep then the stock spare tire carrier will need to be replaced. Heavier tires will cause the stock tire carrier to rip loose from the rear tailgate. As a general rule the stock spare tire carrier is good for tires up to 31 in diameter. When replacing the stock carrier, most people do this when replacing the rear bumper by adding a swing out tire carrier designed for the particular bumper being purchased

Nerf Bars / Rocker Panel Guards Nerf Bars are the U shaped bars mounted to the frame on the side of the jeep just below the doors. They protect the side of the jeep. In selecting Nerf Bars, do not get the ones that have the built in step. They are much weaker and will soon bend. Rocker panel guards mount to the rocker panels. Generally they are not quite as strong as Nerf Bars, but are better suited for rock crawling as the do not give up any ground clearance and do not stick out as far as Nerf Bars. Many modern Rocker Panel guards combine the best features of Nerf Bars and the traditional Rocker Panel Guards. The new Jeep Rubicon comes with Rocker Panel guards.

Corner Panel Guards mount on the rear corner panels and protect the Jeep from getting dents in this area. The new Jeep Rubicon comes with Rocker Panel guards.

Differential guards protect the front and rear differential covers from impact. The differentials are the lowest part of the Jeep and can take quite a bashing in the rocks.

Some other items that can be added are an oil pan skid plate and a stronger gas tank skid plate. The gas tank tends to take more of a beating in the rocks than the oil pan. If you get too big a dent in the gas tank skid plate you can actually lose capacity in the gas tank by as much as a couple of gallons.

2. Vehicle Recovery

Tow Strap as previously discussed. Remember a strap with no hooks.

Winch - Most novices vastly overrate the need for a winch. In most cases a tow strap and a buddies Jeep is all that is needed to recover a stuck vehicle. When off roading with others, a winch, on the average, will only be used on rare occasion. If you go off road by yourself, or find yourself in a precarious situation, a winch can literally be a real lifesaver. In choosing a winch stick with one of the major brand names, i.e., Warn, Ramsey, Super Winch, or Mile Marker, and get one with at least an 8000 lb rating. For use off road, a winch with a high no load line speed is more desirable, than one with a slightly higher line speed under load (Most winches are fairly equal in line speed under full load). Of course it is nice to have both. For a Jeep the Warn Model 8274 is considered the Cadillac of winches, but then it is also the most expensive. Of all the winch manufacturers mentioned above only one is not electric. The Mile Marker winch is hydraulic, utilizing the power steering pump. The engine must be running to use the winch, but is almost impossible to stall and will pull indefinitely without having to pause to cool it off and let the battery recharge a little.

High Lift Jack - A high lift jack is a very versatile tool that can be used as a winch, if you have the patience, and a clamp. It is also good for jacking your jeep off a rock, or even to do something as mundane as changing a tire.

3. The Law of Unintended Consequence comes into play when a Jeep is modified in one area and you have to modify some other area to compensate for the original modification. For example adding larger tires and/ or lockers may overstress the axles, or require a change in gearing. Adding more power, i.e., an engine swap, may overpower the drive shaft, U-joints, and even the transmission or transfer case.

(We are now getting into the modifications that improves off road performance)

Traction and Ground Clearance is really what off roading is all about.

4. Traction

Tires - Tires are what contact the ground and are the primary traction devices. Most Jeeps come from the factory with All-Terrain Tires, which frankly are no good for, serious off roading, particularly here in Louisiana. All serious off roaders mount Mud Terrain tires on their Jeep, even in areas where there is no mud. The large lugs on the tires grip better in the dirt, self clean in the mud, and when properly aired down grip rocks. The most popular off road tire is the BFG M/T (Mud Terrain). Here in Louisiana or where there is a lot of mud, the popular choices in tires are the Interco Super Swamper series, with the king being the Super Swamper Boggers. The down side to Mud Terrain tires is that they do not grip the road as well as All Terrain or street tires. Also with the exception of the BFG M/T's they wear out fairly quickly, around 20,000 miles. For some reason the BFG M/T can go over 40,000 miles before wearing out.

One thing that can be done with any tire to improve traction is to air them down when off road. Although this sacrifices some ground clearance, the tire has a larger contact patch on the ground. To get maximum benefit a tire needs to be aired down to 10 lbs or less. When tire pressure gets this low there is a chance that the tire will lose it's bead and come off the rim. Mud Terrain tires can generally be safely aired down lower than street tires. (If tires are aired down as low as indicated above they must be aired back up before hitting the pavement. This requires an air compressor or some other means to put air back in tires. A popular addition to the Jeep is an on board air compressor)

Sway Bar Disconnects - In order for tires to provide traction they must stay on the ground. The coil springs on the TJ do a much better job than leaf springs used on earlier Jeeps in keeping all four tires on the ground when the terrain gets a little rough. This is why there are after market kits to convert earlier jeeps from leaf to coil springs. One of the biggest improvements to help keep all 4 tires on the ground is to temporarily disconnect the sway bar when off road. This can be made much easier by installing quick disconnects. They sell for a little under $100.00 and are easy to install. It is amazing how much improvement in off road ability disconnecting the sway bar provides. It is very important, particularly on a TJ, to reconnect them before getting back on the road. If you don't, not only will the Jeep sway excessively, but also you will find that the steering wheel is not centered when trying to drive straight down the road.

Lockers - Even with the sway bar disconnected there will be times, more often than the novice thinks, when one or more tires come off the ground. When this happens all the power on that axle goes to the tire that is in the air or has almost no traction. If this phenomenon occurs with one rear tire and one front tire off the ground, the Jeep just went from 4-wheel drive to no wheel drive. (Yes this does happen) To keep this from happening a locker needs to be added to the rear and/or front differential. A Track Lock or other limited slip is not a locker and is useless when one tire totally loses traction. There are three types of lockers.\

A Spool which permanently locks both wheels on the axle together, is not recommended unless the Jeep is going to be used exclusively off road, and should be never put in the front axle. Locking both wheels on the axle means that one wheel cannot turn faster or slower than the other, even in a turn. Spools are mostly used on Drag Racers, which are running in a straight line.

Automatic Lockers - These type lockers engage and disengage automatically. They work by allowing one wheel to turn faster than the wheel receiving power but will not allow one wheel to turn slower than the wheel receiving power. If the wheel not receiving power tries to turn slower than the wheel receiving power then the locker engages providing power to both wheels. With an open differential, or one with a Track Lock, the outside wheel in a turn receives the power, while the inside wheel turns slower than the outside wheel. Just the opposite of what happens with a locker, which causes some quirky handling qualities on the road that takes a little getting used to. If you are aware of these quirks and take extra care when driving on icy roads, an automatic locker in the rear will present no problems to the driver. In a TJ, automatic lockers should not be used in the front, as they can be very dangerous on icy roads. The reason for this is that the TJ does not have locking hubs or even an axle disconnect like the YJ had. There is no way to disengage an automatic locker in the front, unless you add locking hubs in the front through an after market kit, such as the one Warn offers. Some automatic lockers work with the stock carrier just replacing the spider gears. Other automatic lockers replace both the carrier and spider gears. These are more expensive and difficult to install. Since installation requires the ring and pinion to be set up again, installation is best left to the experts. The Lock-Right is an example of a locker that does not replace the carrier, while the Detroit locker replaces the carrier.

Manual Lockers - These type lockers engage manually and when locked work just like a Spool. When not engaged they work just like a stock Jeep with an open differential. This gives you the best of both worlds. You just have to remember when to engage and disengage them. Unfortunately these are the most expensive lockers and are costly to install since they also replace the carrier. There are three currently available manual lockers for a TJ. The ARB Locker, which is engaged by air pressure and requires an onboard air compressor. The Ox Locker, which is engaged with a cable, routed to a lever inside the Jeep. The 3rd manual locker is the one used in the new Jeep Rubicon. It also is an air locker but operates at a much lower air pressure than the ARB Locker. When disengaged manual lockers present no handling problems on the street and can be used in both in the front and rear on a TJ. The Jeep Rubicon has lockers both front and rear.

Lower Gear Ratio - Off road driving is done a very low speeds using engine torque rather than engine power and speed. Torque is increased by reduction in gearing which is why the 2.5 liter four cylinder engine performs well of road although it is somewhat underpowered on the highway, particularly if bigger tires are added. The four-cylinder jeep comes with a low gear ratio, 4.10:1, in the differentials while the six cylinder Jeep comes with a 3.73:1 ratio. (The Jeep Rubicon comes standard with a six-cylinder 4-liter engine and a 4.10:1 gear ratio.) The transfer case provides an additional 2.72:1 low ratio when placed in low range. This generally is a low enough ratio for most off road trails. When it comes to rock crawling a lower gear ratio is desired. This can be achieved in several different ways.

One way is to change the transmission and install one with a super low gear. To keep an overdrive gear, only one transmission is available for this purpose the NV4500. It is longer than the stock transmission, and the Law of Unintended Consequence really comes into play making it fit. Automatic transmissions are a little different and generally are not changed out, as none of them offer a real low range.

A second way is to lower the gear ratio in the differential. This is normally done as the Law of Unintended Consequence when larger tires are installed. A lower gear ratio is required in the differential to offset the gearing change made by the larger diameter tire just to bring the overall ratio back to stock. Of course lower gears than what is required to offset larger tires can be added to reduce the overall ratio. This has the downside of affecting highway operation, as the engine will be operating at a much higher rpm at highway speeds.

The third way is to modify or change the transfer case to provide for a lower low range. There are after market kits available to change the gear ratio on

the stock NV231 transfer case from 2.72: 1 to 4:1 low range. There is also an Atlas II transfer case available in either 3.8:1 or 4:1 low range. A Jeep Rubicon comes with an NV242 transfer case with a 4:1 low range.

5. Ground Clearance

Taller Tires -Most beginners' think the way to increase ground clearance is to lift the Jeep. Actually the only thing that increases ground clearance is a larger diameter tire. This is because the lowest part of the Jeep is the axles and differential. It takes a tire with an increase in diameter of 2 inches to increase ground clearance by 1 inch. Remember that 1/2 the increase in tire size is above the axle and is not providing any increase in ground clearance. It is however bringing the tire closer to the fender, which increases the chance of the tire making contact. If you want to increase your ground clearance by 2 inches then an increase in tire size of 4 inches is required, and it is doubtful the tire will fit. This will usually require that the Jeep be lifted, which has the downside of raising the center of gravity. Not a good thing when a Jeep is off camber on a side hill. Generally you don't want to lift a Jeep any taller than what is required to fit the tires you want to install. Popular tire sizes are 31 inch, 33 inch, and 35 inch. The trend today is toward tires larger than 35 inches as Jeeps are running much harder trails than ever thought possible. Most of the trails, particularly the ones here in Louisiana can be run with 31 inch tires. (Mark Smith back in the 60's led a group of Jeeps from the tip of South America to Alaska in Jeeps running 31 inch BFG Mud Terrain tires and no lockers) A larger tire brings on the Law of Unintended Consequence. As mentioned previously, a change in gearing is usually required. Also stress is being put on the drive shaft and axles. It is not uncommon to twist a drive shaft or break an axle. In the rear the stock Dana 35 can handle up to a 33 inch tire. With a 33-inch tire and lockers, particularly with low gearing, the stock Dana 35 axles will snap. You can add stronger axles, but you still have a Dana 35. A popular swap is the Dana 44 or the Ford 9 inch axle. The Dana 30 up front is usually good up to a 35-inch tire. A Dana 44 is a popular swap for the front axle but is pretty expensive. A rear Dana 44 is an option offered on a TJ, but a Dana 44 is not available on the front except on the Jeep Rubicon. Larger tires also put a strain on the braking system. This involves modifying the braking system to provide for better stopping power. One way to do this is to replace the rear drum brakes with disc brakes. The Jeep Rubicon comes with rear disc brakes.

Lift Kits -With regard to lifts there are two kinds available for the TJ, a body lift and a suspension lift.

Body Lift - Available in 1, 2 or 3 inches. These are spacers that mount between the frame and tub. They are fairly inexpensive and easy to install. The 2 and 3 inch lift will require extending the steering shaft and lengthening the transmission and transfer case shifter

Suspension Lift - Usually available in 2,4,and 6-inch kits. For a TJ these kits are pretty expensive and usually involve changing the springs and control arms. Some kits are more extensive than others. A suspension lift has the advantage of lifting the frame higher off the ground but on the downside causes excessive driveline angles and vibrations. The Law of Unintended Consequence again. To fix this the transfer case has to be lowered, or slip yoke eliminator has to be added to the transfer case along with a longer rear drive shaft with a CV joint. The fixed yoke on the transfer case has the added benefit allowing the Jeep to be run with out a rear drive shaft in an emergency. Without the fixed yoke, the transfer case fluid would leak out when the rear drive shaft is removed. The Jeep Rubicon comes with a fixed yoke on the transfer case.

If you already own a Jeep and take it off road, sooner or later you will be making most if not all the above modifications. If you haven't bought a Jeep yet, buy a Rubicon. Get all the modifications commonly made, except for larger tires and the resulting required lift.

Source: Lousiana 4x4 Club
Over The Hill Newsletter Vol. 9, Number 8, Aug. 2003


last updated 16 Apr 2004