My opinion in based out of jeep CJs and observations over a considerable period of time. I cede direct cherokee knowledge to 'jack.
A lot of us knows the advantages to a locker on the trail over a standard diff or a limited slip, but just in case someone search threads in the future, Here is a quick run down in blue.
98% of the vehicles on the road have a "open" Differential this is how power is transferred left and right from the drive train and turn corners. Usually this is though a ring and pinion gear inside of which is the spider gears. all housed together in a carrier. The open differential is the most paved road friendly seem less and easiest on mechanical parts and tires. Any part of your drive train only has to ever take half the torque load because the differential splits it. When you turn corners the out side tires have longer distance to travel, the drive trains power is transferred to the OUTSIDE tire and the inside tire momentarily coasts around the corner once speed equalize both tires receive power again unless there is a loss of traction. In this case all of you power takes the path of least resistance. You find this at the supermarket when someone stomps on the go-fast pedal around a corner in a wet parking lot or parked in a ditch in the snow or in our case out on the trail. The problem with a open diff is your power is easily lost when things are slick.
Which brings us to TRASH LOK (traclok, pwrlok and posi, these are all brand names) These are usually factory installed optional LIMITED slip differentials these use friction to transfer some power left and right even when your vehicle is in a situation where traction is marginal to one side or the other. They often require special gear oils or a additive. Inside the carriers are different than a open diff although the ring and pinions are the same. The problem with factory installed limited slips is the average buyer does not need them, so they tend to be "soft" and not useful to the average trail jeeper. The clutch packs tend to wear out quickly especially if the vehicle corners a lot in its life time and a limited slip is worthless or next to it when situation get really technical as its effectiveness is lost. There are some "tight" after market limited slips which can use clutches, cones or even Gleason-Torsion gears or worm gears to transfer power left and right while allowing cornering ability that is easier on parts and tires. These are excellent for front axle situations.
The next diff choice is the SPOOL or "lincoln locker" (a welded diff) This is a strong hunk of metal that replaces the carrier and locks both axle shafts together permanently. This allows no differential left or right in the differential (that sounds weird) basically there is 100% power to all components 100% of the time, when you corner tires with scrub and the drive train binds. This binding is very hard on tires and components on paved roads, and turning tight is right out. Spools are great if you are drag racing or never see a paved road.
A locker is available is several forms. First up is the proper locker like a Detroit no-spin locker being one of the first on the market. This was developed for drag racers or off highway drivers that needed or wanted a spool but still needed to turn corners. This replaces the carrier in the differential and locks the axle shaft together in a way that both will always turn and have power equal to the ring gear 100% of the time. That is left or right or both tires turn at the same speed as the drive train no matter what. It however allows a tire however to coast faster than the drive train around a corner however. Just opposite of a open diff the INSIDE tire has power in a corner as the speeds equalize the gears in the locker which are spring loaded re engage with each other this is famously "harsh" and on paved roads especially on slippy days causes unpredictable behavior unless a lot of care is taken in your driving. It is very easy to swap ends in a short wheel base jeep as it is light in weight and often has a high power to weight ratio. True locker are always "on" so those of us "blessed" with inner axle disconnects and no locking hubs in front axle applications are going to be spinning the drive train even in two wheel drive with out power going forward. just like a spool a locker forces 100% or more of the drive trains power on to all components if you have a weak link in your drive train a locker is going to find it. The reason I stated or more is because as the locker engages and reengages it shock loads the drive train. The biggest advantages to a locker is each wheel in the axles WILL have power. the disadvantages are beefing up a drive train that was not made to handle those power loads, cost and handling characteristics.
"Lunchbox" lockers came around with the lock right and soon after the Detroit version way back in the 1980's They are designed to take a open differential and turn it into locking differential often with out disturbing the ring and pinion gear or carrier this saved considerable cost not only in the locker but it was something that could be done in the driveway in 45 minutes or so. These are not as strong as a "true" locker because you are limited by the stock carriers strength and it has all the advantages and disadvantages of a true locker initially they were just as harsh upon engagement but some of them have been adjusted in design to be a little more road friendly, they still need care on the road though.
Finally there are the "demand" lockers, these are almost as ancient as open differentials these can be actuated by cable, pneumatically (air), Hydraulic or electrical solenoid. They also replace the carrier which adds to the cost and complexity to it. The advantages and disadvantages are that they are either ON or OFF spooled or not spooled. Some of them are even available with a limited slip or full on lock (the rubicon's rear and selected aftermarket products)
Now that the explanations are finished what else needs to change in addition to the locker? Lockers add traction the efficiently force drive train power thought the axle to the wheels. This adds a good bit of strain to ALL components not only in the drive train and axles but the suspension too! This strain will find your jeeps mechanical weak links in short order, and every drive train has a "fuse" Personally I like cheap easy to replace manual locking hubs or drive shaft U joints. My feeling is you will know what you break after a few trips and breaking anything more than twice means you should be carrying a spare. You can marginalize your weak links by driving with care and finesse, be careful with you power applications, crawl at slow speeds and avoid spinning tires in the air a spinning tire will come down an shock load EVERYTHING into 'Xplody BOOM. I used too wheel with a local club that used to gather at a obstacle and listen to what broke, then debate what it was by the sound that it made before recovery and repair, generally the consensus was correct, and got kind of expensive. This falls into what 'Jack wrote above. It may be better to find a appropriate axle swap and build a whole axle up for a locker than to build up what you already have, if starting from scratch depending on what it is they just will not take the strain. Sometimes you will get into a situation where the increased traction of the locker will be at odds with the terrain, The jeep WILL lose these contests with either stalling or breaking parts, Light duty axle housing can bend or spin in the diff housing, springs can collapse over time due to suspension wind up and mechanical parts fail as mentioned if you do not take into account of the kind of loads you are putting on them. Keep in mind those loads are not just the locker, but your engine power, multiplied thought your gear train it also includes tire size and weight , ground resistance, vehicle weight, weather and a bunch of other engineering babble that only Dave completely understands. (sorry Dave).
I mentioned above extra care on paved roads with full lockers and to a extent limited slips. in wet or icy roads even mud a locker puts down your power equally left of right, when you traction is limited and your dirve train does not slip, the vehicle can! the problem is this is unpredictable and it can happen very quickly. This is exasperated by power, speed, short wheelbase, light weight and manual transmissions. Further every vehicle will handle differently in the same situation. Some examples, In my Rubicon pulling out on on Rt194 on a hill in the rain I go in to power hitting second with a limited slip only and "walked" my rear out left and right suddenly before traction improved. Normally in dry weather nothing would happen or at worse the drive train will "load" the suspension a little. Another situation While riding with Tom in his CJ7 with a lock right entering I83 off paxton street in a slushy morning Tom hit third and accelerated his locked rear axle did not have the traction to put the power down so we collectively spun 3, 360 degree a "top" like rotations entering the highway proper, hit 4th and continued on our way, I think everybody near this needed to change pants afterward. My 1982 generally has never spun out I think due to weight longer wheelbase in equal circumstances. Now my 1981 CJ the short time I ran a lockright in it, was very susceptible to spinning out, it was light in the rear and was geared pretty high so it accelerated pretty quickly.
That said, I am locking up ALL of my jeeps to an extent of another, it allows you to overcome a obstacle that normally you could not and it is easier on the jeep to do things slowly and in control than with the stupid pedal to "bump" over them. The advantages are great, you just need to take a look at what you got, what kind of loads you are putting on those parts and what is going to fail when you push your luck.
Some examples using my experiences:
Narrow track 1981 CJ AMC20 I have a lock right for it, and 2.73 gears Not exactly conducive to crawling about and the axle housing is known to spin the axle tubes or bend the comparatively light weight axle tubes, the two piece axle shaft are probably rusted into one piece now but a locker will probably spin them, Status, still uninstalled $230
Wide track 1985 CJ AMC20 3.54 gear and a lock right, this came out of Tom Kigers CJ it has had a variety of one piece axle shafts in it, but Tom could not seem to keep bearing in it, I suspect that it is bent. That said he ran this as a daily driver for a very long time.
Wide track 1982 CJ Dana 30 , I think it has a tracloc limited slip in it, honestly, I have not broken the diff to find out. it does seem to do better than my 1981 cj.
Matt's wide track 1983 jeep CJ had a factory limited slip in it, when it was worn I never noticed a difference between a open diff, after it was rebuilt it did add a little to his jeeps performance, especially with a little application of the E brake to "fool" it.
IH Dana 44 I put a proto type WARN full floater axle kit into this semi floating axle. Originally it had a limited slip in it now it runs a ARB air locker, with 4.27 gears, this was my daily driver for 12 years best of both worlds spooled or locked but expensive around $1800 or so. The advantages of the WARN full floater kit was first, my bearings no longer retained the axle shafts which when failed at 45mphcaused to much excitement on a date on rt 996. Second it added spindles and multiple bearings to carry the vehicle weight taking some strain off the axle shaft. The working load of my original axle shafts was around 90000psi which by today's standards is pretty stout however the WARN axles shafts are rated at loads above 2400000psi per half and if something fails it will be the locking hub on the outside of the spindles. The limits on this are my dana 44 housing which could be bent I suppose but that is unlikely in my application, and drive train wind up twisting my rear springs, I think this is part of the reason I needed higher spring rates in the back. Other things to consider is your gearing and tire size in my case my 1982 puts out around 370fps or torque multiply that out with the transmission low of 6.32 the transfer case of 4 and the rear axle of 4.27 then take into account the vehicle weight and my 35" mud tires and you will start to see coupled with a locker I think that any tire size is limited to this jeep, any more and my drive train starts to get pretty marginal in strength.
Rubicon, gwad stilling paying dearly for this one, you can have your cake and eat it too. But keep in mind that a Rubi's dana 44s are NOT that much heavier than dana30 in terms of housing strength and axle shaft strength, it is a very stout package for stock up through 33" after 35s it get real marginal with drive train loads. Some of my concern with my rubi is that there is NO manual locking hubs to use as "fuses" and worse, much like the cherokee's it has unserviceable unit bearings which complicate axle repairs.
