Hello, my name is Marc Bowers and I am a new staff writer for Cherokee America. My primary goal in this section of the page is to bring informed technical presence to every issue. My background includes over 5 years as an auto/truck technician at an independent repair facility and 2 years as a technician at Town & Country Jeep/Eagle/Chrysler/Plymouth in Seattle Wa. I am both ASE certified and also Chrysler certified. I have been a Jeep owner for several years and have owned a 1977 Grand Wagoneer, 2 Jeep CJ?s (78?CJ-7 and an 81 CJ-5) and currently drive a heavily modified 85 Jeep Cherokee. In this first column I will attempt to shed some light on the often misunderstood area of stock differentials and their aftermarket replacements, both limited slips and lockers. As I feel this area will take some space to fully explain I will write a second part to complete the explanation and delve deeper into the concepts of gearing versus strength and reliability in the next issue of Cherokee America.

In most cases, Jeeps come from the factory with what are called open or standard differentials. These units perform the best for the most people and are cheap to produce. They work by allowing the wheels on each end of an axle to travel at different speeds, making for much easier cornering and low tire wear. Power is actually only directed to one tire at any given time through the use of GEARS in the center of the differential unit. What this means is that technically most ?4X4s? are actually 2wd with available power traveling to one tire in the front and one tire in the rear. The only problem with the stock arrangement is that under all circumstances the power coming from the driveshaft goes to the wheel with the least amount of traction. Think of water traveling downhill, it will always take the path of least resistance. This is most likely to be a problem under more extreme conditions such as when the suspension is ?crossed up? with two wheels off the ground (or nearly off the ground) at opposite corners of the vehicle. What happens next is the wheelers worst nightmare, forward motion is lost as your tires dangle helplessly off the ground spinning. There are times when this can be dangerous. For example, losing forward motion on a large hill climb can force you to back down, always a tense moment, as control is easily lost when backing down a hill. Those are the drawbacks to open differentials.

The first step up from the standard differentials are what?s called a limited slip diff. (sometimes called a posi-traction, coined by Chevy in the 60?s for their own limited slip diffs). These units can be either factory installed (like the Jeep/Dana Tracloc) or you can buy and install aftermarket units. Limited slip differentials get their name from what they?re supposed to do, limit slip between two wheels on a single axle providing more traction by sending power to both wheels instead of just one, yet they are also designed to allow slippage between those same two wheels when negotiating a turn. This is absolutely necessary for decent handling and tire wear, but there are some disadvantages as well.

The downfall of the limited slip comes at the extreme end of the four-wheeling spectrum. These units will fail to provide additional traction when wheels are lifted off the ground and resistance at one wheel is vastly greater than the other. In these situations once again you will be left in one place with your wheels spinning helplessly in the air, forward motion stopped. ,In addition, most limited slips use clutches inside the differential assembly that limit slip, as those clutches wear the differentials ability to stop ?slip? decreases substantially from new. In turn, once this wear begins to happen the diff will act much as an open diff does and only send power to the tire with the least resistance. Jeep factory Trac-loc diffs are notorious for this kind of accelerated wear and will often be worn out in less than 40K miles. The best thing about limited slip diffs is that they have little or no effect on the everyday driving character of your Jeep except in icy conditions where slipping sideways on a sideslope can be a problem if both rear wheels spin and traction is completely lost. Typically open diffs won?t do this as only one tire spins on each axle and the other stopped tire acts as an anchor keeping the vehicle from sliding sideways.

The last type of differential option available to the Cherokee owner is what is termed a locking diff, or locker as it?s often called. Jeep does not offer this type of diff as an option on any of it?s vehicles from the factory and I don?t believe they ever have. Full locking differentials can be your best friend or your worst enemy depending on the situation . You see, these units do as their name implies and they are able to get power to both wheels on the same axle regardless of whether one, both, or neither of those wheels are touching the ground. Using special interlocking spring loaded dog clutches (imagine your fingers locking together to lock your hands) allows the wheels to turn at different speeds when negotiating a turn on the road and then lock together when power is applied forcing the two wheels to operate together for maximum traction in rough terrain.

The advantage is obvious, in low traction situations where wheels are being lifted off the ground or one side of the Jeep is on a very slippery surface, such as mud or snow, the other tires with weight and traction will continue to pull you through the trouble spot.. Most of the locking differentials on the market are very torque sensitive making them extremely positive in their locking action. What this means is you get stuck less and the diffs make you look like a hero at your favorite wheeling spot.

Unfortunately , there is no free lunch, these diffs have some disadvantages also. First the very nature of the locking action creates a diff that can be noisy and somewhat abrupt. Second, the driving feel of your Jeep will change with an automatic locking diff, corners will have to be taken slower and smoother when driving around town as the differential locks and unlocks in the corners, unsettling the tail of the Jeep a bit and making the it feel less planted ( Next issue I will get into manual locking diffs like the ARB and new Powertrax manual locker soon to be on the market, and yes these are the best of both worlds, though beyond most peoples price range). This is mainly something you have to get used to more than it is a problem. Also driving in icy conditions will cause sideslip if all wheels are allowed to spin causing the Jeep to be harder to control in this situation. Another concern most people don?t think about when considering installing locking diffs is they will allow your vehicle to travel into much more difficult terrain. It?s very easy to make the Jeep more capable than your own driving skills should allow, for this reason I don?t recommend lockers to novice off-road drivers.

Finally, there is the question of wear and potential breakage being ?caused by the locker?. The possibility of breaking parts can go up as you have the ability to send 100% of all available power to a single tire with no weak traction links in the chain. However, in my experience (I run a Lockright in the rear, my front diff is welded shut) breaking parts may actually be harder to do if you prefer finesse over speed. With a locker replacing one of your factory open differentials you will be able to crawl over obstacles that would have required speed and momentum before, going slower usually reduces the chance of breakage.

In closing this month, I hope you understand the pros and cons of the different differential options available for your jeep. Next time I will try to bring up to date info on the different choices available from various manufactures of both limited slip and full locking differentials and help you decide what options and features are available that fit into your own budget.

Differential Types (Part 2)

Last month I covered the basics of differential types and options available to the Jeep Cherokee owner. As promised this month's article will be focused on strength issues and different options for you in your quest to build your ideal Cherokee. As an aside I will also explain selectable lockers and their operation. Finally, I have created a list of the most popular Aftermarket differential units on the market. Included is information on difficulty of install and strength of the unit being presented. I must acknowledge that the manufacturers are in no way sponsoring this article and that some of the information shown here is based on friends who have used these different diffs over the years. I have also attempted to gather accurate information from the manufactures in regards to design and operation.

Currently the only selectable locker available for the Cherokee is produced by ARB in Australia. This unit is operated using compressed air to lock the axle side gears together when a locking switch is pressed giving maximum traction. Powertrax Corporation is developing a selectable locker for the Cherokee called the Command Locker, but as of yet it is unavailable.

Tractech E-Z Locker: $235.00
E-Z Locker is an inexpensive locker designed for occasional off-road use. Tractech doesn't recommend tires any larger than 32 inches be used with this locker. Installation is kept simple as this unit reuses the factory installed open differential carrier to house the locker. Installation can be accomplished at home in just a few hours with normal hand tools and nominal mechanical skills. Operation of the E-Z locker can be a bit harsh on dry pavement at low speeds. Banging sometimes occurs as the clutches lock and unlock. Off highway performance is very good with this locker.

Powertrax Lockright: $290.00
Lockright locking differentials are similar in design to the E-Z locker, utilizing the factory differential carrier to house the locker. Installation is very similar to the E-Z locker and requires only normal hand tools and mechanical skills. Powertrax does not offer any limitations on tire size with their unit and it is sold as a hard-core locking unit. Operation of the Lockright can be described as noisy at times with ratcheting and banging of clutch teeth quite noticeable. My experience with the Lockright is that the unit is extremely positive and therefore causes some driveability problems on the street. Off-road locking action is exceptional and trail manners impeccable.

Tractech Truetrac: $375.00
The Truetrac from Tractech is the exception to the rule of limited slip differentials using clutches. The Truetrac uses a unique gear system to limit slip when placed under a load. Long lasting and not prone to wear at high rates these diffs should last as long as the original factory parts. These units are very smooth and a good choice for installation in a front differential as they don't hamper steering ability as a locking diff can. The downfall of the Truetrac is the inability to completely lock. It is simply less positive and therefore doesn't offer as much traction as a full locking differential. This unit is excellent for people who occasionally travel off-road and would like additional traction without any noise or loss of driveability. Installation requires removal and replacement of the complete differential carrier unit and will need to be performed by a qualified technician with appropriate tools.

Tractech Detroit Soft-locker:$500.00
The Detroit locker has been THE heavy-duty locker used by four wheelers for many years. Using it's own differential carrier unit the Detroit locker is extremely strong and capable of withstanding severe off-road punishment. Installation requires a skilled technician with appropriate tools for "setting up" the differential. The Detroit is ideal for those individuals who like an automatic locker and demand total reliability. On road performance is similar to other lockers though may be a bit smoother and quieter than the Lockright and E-Z Locker.

ARB Air Locker: 650.00 + 185.00 for air compressor and install kit.
The ARB Air Locker is the ultimate locking differential. With it's ability to operate as a normal open differential and at the touch of a button to be a fully locked unit it suffers none of the pitfalls of automatic locking diffs. Installation requires the same skills and tools as with the Detroit Locker. Also needed with the Air Locker is the ARB air compressor used to operate the unit, adding to the initial cost. The ARB is designed to be extremely strong and reliable so breakage is unlikely with this unit. Cost is the single biggest downfall with the ARB as installation can add considerably to the total price.