Planet 4x4 - Lockers, Positracks, and Limited Slips Explained

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All About Lockers, Positracks and Limited Slips. Explained

Lunch Box Lockers, Full Lockers, Spools, Limited Slips, Positraction, Lincoln Lockers, and Open Diffs. You've heard the words, but what does it all mean?

It all has to do with how your rigs power gets put to the ground through the differential in the axles. The most common setup from the factory is an open differential. This is a street friendly setup that puts power to the tire with the least amount of traction. This makes cornering on the street easy and makes your tires last longer. However in an off road situation where one tire gets lifted, it will be the one that will spin and you will go nowhere fast. There are a few ways to tackle this problem, all with their own pros and cons.


Limited Slip or Posi Trac- A Limited Slip or Posi Trac is the same thing. There are clutches inside the differential that allows power to be transferred to both tires at the same time. There are different approaches to this as the clutches can be in different locations or some other type of torque transfers system is used. What is all boils down to is that some power will be sent over to the tire with the most traction. This power transfer can range from low like 30% to up to 90% or more. However all power will not be transferred as the design is supposed to allow some slippage. This is so that the vehicle will still remain street friendly and tight turns will be easier on the drive train. This is an option on performance cars and on some trucks. These can make a real difference in the performance of your rig and it is very common to find them up in the front diff so steering is still reasonable but traction is improved. Look at the picture on the left and you can see the springs in the center that apply pressure to the clutches. The harder the spring, the more torque transfer.

Automatic Lockers- An automatic locker applies 100% of the torque transfer to both tires but will allow the wheels to disengage for some street manners. But here's the trick, a locker will allow one wheel to spin faster then the driven wheel. This means that when accelerating around a corner, the locker will drive the inside tire and will allow the outside tire to ratchet ahead. This will try to force you strait when on the throttle in a corner. If you coast the corner it will behave fine. When both wheels are turning at the same speed it will lock back up. This locking and allowing one tire to turn faster then the driven tire can make some good popping noises on new lockers. Once they wear in, they usually shut up. Pro's are they work great. Cons are they can break on you.

Lunch Box Lockers- A lunch box locker is an automatic locker that replaces only the spider gears. These are the four little gears in the center that allow the tire with traction to not move when you need it to. You can install these in the driveway without pulling the carrier or resetting up the gears. Its one of the most popular options for its ease of installation and usually they are not too expensive. Lock Rite and Detroit offer these type of lockers. Also Aussie and Quick loc offer their own versions. Below is an exploded view of a lunch box locker. Pro's are that anybody can put one in. Cons are they are the weakest type of locker and big tires can kill them.

Full Carrier Lockers- A full carrier locker is an automatic locker that also replaces the carrier for the ring gear with a stronger version and houses the locker itself. The only one worth mentioning is the Detroit Locker. This was first designed for the military and is available in many applications. Pro's are is very strong and Cons are it is expensive and you have to set up the gears again as the carrier is changed out.

Spools- A spools replaces the spider gears and connects both axles together for full power to both tires all the time. There are two kinds. A mini spool (left) that just replaces the spider gears, and a Full spool (right) that replaces the carrier. A spool is great for the most extreme type of wheeling. Pro's are they are cheap and the mini spool is easy to put in plus 100% power to both wheels all the time. Cons are bad handling on the street and can be difficult to turn. This can be hard on axles and tires.

User Controlled Lockers- A user controlled locker is a locker that the driver can engage and disengage at will. There are several different kinds and the most popular kinds are the Air Locker, the Electric Locker and the Cable Actuated Locker.

Air Lockers- An Air locker is a locker that is actuated by air pressure delivered through an air line routed into the differential housing. The only real player in this market is the ARB air locker. The Pros are a good locker with control at the push of a button. The Cons are you will need an air source to run it (ARB sells a compressor for it) and the air lines can be a maintenance issue.

Electric Lockers- An Electric Locker is the same as an Air Locker but instead of air, it just needs a power source to lock it in. There are a couple of different versions. Some are Limited Slips when off and some are open when off. This type of locker has come in stock Toyota's for years. Aftermarket versions are available from Eaton, and Auburn and maybe elsewhere. Pro's include easy to wire and to use. Cons include cost and availability and installation.

Cable Actuated Locker- The only real cable actuated locker on the market is the OX Locker. This locker works like the above but a cable and handle assembly that is mounted in the cab is used to engage and disengage the locker. Pro's and a solid shift that you know is locked, Cons are it can be hard to lock in while bound up and cost and installation.

Lincoln Locker- A Lincoln Locker is a spool that is made by welding the spider gears up in the housing to create a permanent spool. It has that name because you can use your Lincoln Arc welder to do it. Pros are you can do it for the price of the rod and in your driveway. Cons are you now have a permanent spool which might be fine for a rig.

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