For example I hear about "detroit lockers", etc.
OK, I'm going to start very basic, since I don't know your skill level...
"Detroit" is a brand name, like 'Spicer', 'Bendix' or 'MSD'...
They make VERY tough drive line components and have a very good reputation for durability.
Some other 'Locker' brand names are OX, Aussie, Lock-Rite, ARB, ect.
The term 'Locker' comes from people saying the 'High Traction' differential carriers 'Lock' the rear wheels together during operation.
Normal operation, you don't need a 'Locker', and if the rear wheels are 'Locked' together, you can't go around corners without twisting one axle or the other.
When you go around corners, one wheel MUST move faster than the other since the OUTSIDE wheel has to go a farther distance in the same amount of time the INSIDE tire does.
'Open' differentials will allow one wheel to 'Free Wheel' to accomplish this turn radius difference.
If you have the wheels locked together,
You will be twisting axle shafts, skidding tires on the pavement or the vehicle will find some way to balance the load being inflicted on the differential/axles/tires by that different loading side to side.
I've seen MANY a broken axle from the stress,
And when the two wheels are locked together, the vehicle steers very strangely since the BOTH wheels are trying to push the front end straight down the road instead of turning.
What a 'Locker' does is allow one wheel to 'Unlock' when you are going FORWARD around a corner, and you aren't applying enough power to make either wheel slip on the pavement.
If you apply power around a corner, and one wheel slips FORWARD, the differential carrier will 'Lock' both wheels together and one of two things will happen,
1. Both wheels spin and the back end swings around very quickly since all the differential/tires are trying to do is 'Get Straight' and unload the uneven force.
2. You will push the front tires in a straight line with the rear axle, no matter what direction the tires are turned to.
3. If you spin the tires fast enough to brake BOTH tires completely loose, you will come completely around and be facing the 'Wrong' way very quickly!
Since BOTH tires have no traction to speak of, the momentum of the vehicle will carry the back end right on around, usually scaring the crap out of anyone unlucky enough to be coming at you in traffic!
Now, since 'Lockers' are designed to 'LOCK' when the tires are rotating FORWARD, you get some even stranger things going on when you are in REVERSE!
Some people call it 'Fork Lift' steering, and they are VERY close to being correct, but not for the same reason forklifts do strange things...
Lockers do STRANGE THINGS in gravel, on sand on the roads, they are virtually uncontrollable on ice...
That's why some lockers are 'Selectable',
Meaning you can turn the 'Locking' feature 'On/Off' at will.
This lets you drive SAFELY on highways, rock roads, places where they have scattered sand or sand has blown onto the roads...
And you can turn it 'Off' when you are on wet pavement, ice or on gravel/sand so the back end doesn't jump out from under you without notice.
There are the 'Gear Driven' & Clutch plate differentials called 'Limited Slip' units, since true 'Lockers' are inherently unsafe on highways...
(let the flames begin, but there is a reason they aren't installed in passenger cars anymore)
The clutches allow a limited amount of power to reach both wheels, and when one wants to Unload, it can 'Slip' the clutches and do so safely for both the driver and differential/axles.
The draw back to clutches is they wear out quickly and leave you with an 'Open' differential,
They WILL NOT give you power to a wheel that has traction if the other wheel has NO traction,
Say on wet clay or ice,
And they require specialized maintinance, additives to keep the clutches from binding, ect.
About 1970 or so, All gear driven Limited Slip Differentials came into common use,
And they are the next step in evolution for the Limited Slip.
The gear driven differentials (Detroit 'TrueTrac', ect.) will apply a 70/30 split to the wheels so BOTH wheels will get some power no matter if one is off the ground!
They don't pop, crack, spit out clutch plates and they pull on BOTH wheels.
The secret is, no matter how long or short the turing radius is of any vehicle,
One tire is NOT going to exceed the wheel speed by more than 70%,
So the gear sets can transfer AT LEAST 30% of your driveline torque to the wheel with the MOST traction, no matter what.
I've gone through a BUNCH of lockers of all styles,
And the Detroit TrueTrac has done the best job for me in the back of my vehicle...
Never has to be turned 'On/Off', is always ready, never does anything stupid, doesn't load/unload unexpectedly and doesn't make the first noise in operation like other Limited Slip or Locker differentials do.
Then you get into full on 'Lockers'...
The most popular is the 'Lunch Box Locker'...
Named from an article in a magazine a few years back.
The premise was...
Because you can take one to work in your lunchbox, and install it over your lunch break...
Silly name, but the name of that article stuck like glue!
Anyway, 'Lunch Box' lockers are CHEAP! Around $200 to $300 for most axles,
And they fit in the factory 'Open' carriers,
So you don't have to remove the carrier or set the ring/pinion gears back up like you have to when you replace differential carriers for a Full Size locker.
I run one in the fronts of Dana 30 equipped jeeps that have lockouts on the hubs and two wheel drive transfer cases...
By unlocking the hubs and putting the transfer case in 2 wheel drive, you have 'UNLOCKED' the locker in the front and it's not going to do anything stupid while you are on gravel or pavement.
Since the Dana 30 is such a weak axle all around,
Small ring & pinion that likes to break,
Weak U joints between axle pieces, Ect.
There really isn't any sense in spending a bunch of money on a Dana 30 front axle,
You are MUCH better off with a Dana 44 in the front to start with if you are 'Serious',
Or just keeping the Dana 30 mostly stock, adding a $200 LockRite or Aussie 'Lunch Box' locker to it and going down the trail with a big grin on your face if you aren't a 'Hard Core' wheeler...
Most of the time, I tell the part timers that come in here to look for a factory limited slip, rebuild it with new clutches and it will do everything a 'Cheap' locker will do without the headaches full time lockers bring to the table...
Or if they have a fat wallet, go with a TrueTrac gear driven limited slip in the rear...
That way, you have 'Posi', or both wheels turning in the rear, without remembering to 'Turn On' the locker, and 'Turn Off' the locker when they are done,
And don't have the driveability problems that come with 'Full Time' lockers...
If you are a serious wheeler, you WILL want to spend CUBIC DOLLARS and get a 'Selectable Locker' you can turn on and off at will from the drivers seat...
Serious wheelers will have LARGE, AGRESSIVE tires that don't like to be skidded and give great traction, so they will load the axle shafts to no end when going around corners,
And if they are 'Serious', they have enough horse power to push the front end stright no matter which way the wheel is turned...
Selectable lockers are NOT CHEAP!
But they ARE the only way to get around tight turns on slick trails without getting in and out of the vehicle all the time...
They will cost you $1,000 by the time you buy them,
Regear for large tires, and have them installed!
Since I have to run wiring, cables, compressors, tap electrical circuits, ect.
I won't touch a selectable locker install for less than $500 an axle, and the lockers are normally $750 to $1,250 each before gears and install.
The 'Cheap' way to go for someone 'Semi-Serious',
IE: Vehicle is still street driven and is leagal for streets, but you still get into the 'Out Back' with it on weekends)
Is a $650 True Trac in the rear, all the qualities of a full on 'Locker' without having electrical/air/cables to turn them On/Off.
They are a full size differential carrier, so you WILL have to set up the ring/pinion again, and that should run $250-$300 in a reputable shop.
In the front, if you already have lockouts on your hubs and 2 wheel/4 wheel drive transfer case
(NOT FULL TIME TRANSFER CASE!)
Then consider a 'Lunch Box' locker for the front.
Easy to install, doesn't 'Eat' anything or do anything stupid when in 2 wheel drive.
About $200-$300 for the locker and another $75-$150 for install if you don't do it yourself.
I haven't been 'Stuck' since I went 'TrueTrac' in the rear and 'Lunchbox' in the front with my highway driven Jeep, and I'm in the often VERY MUDDY river bottoms on the farm about 3 days a week...
And I take it to the local 'Off Road' parks, drive it there, and drive it home afterwards...
I'm not saying you won't get 'Stuck', I'm saying that you will do things with that Jeep you sure couldn't have before!
(Winch is ALWAYS a good investment if you get into the soup very much!)