Default Lockers & Limited Slip Differentials 

Old 01-17-2012, 10:49 PM   1 links from elsewhere to this Post. Click to view. #1
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Types of Traction Aids

Open Differential
The open differential is what is installed in the majority of all vehicles from the factory. It isn’t a traction aid. If one tire is on poor traction or starts to lift off the ground it will spin and the other tire won’t be able to apply any more torque to the ground either.
Advantage: excellent directional stability. If one tire spins or looses traction the other tire can keep the vehicle moving in the correct direction.
Disadvantage: You are most likely to get stuck with an open differential.


Limited Slips
A limited slip differential will aid traction. If one tire starts to slip a limited slip will apply more torque to the tire that has the best traction. The amount of torque that it applies to the tire with the best traction depends on the bias ratio of the limited slip. The higher the bias ratio the more aggressive the limited slip is and the more torque the limited slip can deliver to the tire with the best traction. A limited slip with a bias ratio of 4:1 (also called a 60% locking factor) can deliver 4 times more torque to one tire than the other.
There are three types of limited slips:
Plate clutch limited slip – these differentials have alternating friction plates. You can tune these limited slip differentials by changing the order and number of friction plates to get a very high or very low bias ratio. Needs a special oil or oil additive for the clutch such as Amsoil Slip Lock.
Cone Clutch limited slip – These differentials have a cone shaped clutch on each axle shaft that grips the differential to help send torque to the tire with the best traction. These limited slip differentials are not tunable. In many cases they are not even rebuildable. This is because the cone grips the differential case itself. When the case is worn the whole differential must be replace. Also needs a special oil additive.
Gear type limited slip – These limited slips are a much different design from other differentials. The specially designed gears bind as one tire spins. This type of limited slip does not require a special additive in the oil.


Automatic Lockers
A locking differential can deliver 100% of the torque to one or both tires even if one tire is off the ground. A locker can unlock to allow some differential action going around turns.
Lockers provide excellent traction to keep the vehicle from getting stuck but they also have the poor directional stability. If you give it a little too much gas going around a turn you can fishtail and loose traction. A locker can always keep you moving but you may not be moving the direction you want. This is not a big problem as long as you are careful when you drive on the street.


Selectable Lockers
A selectable locker (also called On-Demand locker) can be turned off or on. This is the best of both worlds. You can have an open differential for street use when you want control. Then when you are off-road and worried about getting stuck you can activate your locker and both tires on the axle will rotate in unison. Selectable lockers activate with different methods. Some use compressed air to lock the differential. Some are cable activated and the driver moves a small lever. Some selectable lockers are electrical and the driver presses a button to activate the locker.

Selectable lockers have two disadvantages:
1. They cost more
2. They are more involved to install. They may need an air compressor, air lines, cable or wiring.


Spool
A spool will rotate both axle shafts in unison at all times. They are not recommended for street use.

Spool

Credits: Information for this thread was gathered from several sources. Unless otherwise stated photographs came from the manufacturer's web sites.
The most important source of information was the book "Differentials: Identification, Restoration & Repair" by Randy Lyman and Jim Allen. An excellent book on the topic.
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Default Auburn Pro Series Limited Slip 

Old 01-17-2012, 11:31 PM   #2
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Auburn Limited Slip
Cone Type Limited Slip

This Limited Slip is offered in two versions: High Performance Series and Pro Series. The Pro Series has a higher bias ratio of 3.5 to 1.
These are both cone clutch limited slips. You must use a limited slip oil additive in the differential.
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Default Truetrac 

Old 01-18-2012, 12:06 AM   #3
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Truetrac
Gear Type Limited Slip


The Truetrac is sometimes called a Detroit Truetrac. It is made by the same company as the Detroit Locker but the TrueTrac is not a locker. It is a limited slip.
A gear driven limited slip such as the Truetrac does not need a limited slip additive in the oil.

The Truetrac is a gear driven limited slip.
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Default Powr-Lok 

Old 01-18-2012, 12:37 AM   #4
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Powr-Lok
Clutch Plate Limited Slip

The Powr-Lok has been built by the Dana-Spicer corporation since the mid '50s. It is a clutch plate limited slip and for that reason needs a special oil or oil additive for limited slips. The Powr-Lok was originally an OEM limited slip but now it is only available aftermarket.
The Powr-Lok is easy to tune for high or low bias. The thing to remember when tuning the Powr-Lok is there needs to be 5 clutch plates on each side of the differential. These clutch plates can be flat, curved or made of different composition. What five plates you use and the order of the plates will dictate the bias ratio (how much torque gets applied to the tire with the best traction)
You must use a limited slip oil additive in the differential.

Powr-Lok
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Default Trac-Lok 

Old 01-18-2012, 10:23 PM   #5
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Trac-Lok
OEM Clutch Plate Limited Slip

The Trac-Lok is based on the Powr-Loc but it is not as strong. It has 2 spider gears whereas the Powr-Loc has 4. The Dana-Spicer corporation has built this limited slip since the 1970's. The earlier versions were known for cracked cases but newer units are better. This is the most common limited slip to come from the factory in a CJ. You must use a limited slip oil additive in the differential.

The Trac-Lok looks like an open differential but it has clutch pads behind each axle gear. Notice the rounded shoulder of the open differential.
These limited slips are easy to rebuild and tune.
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Default Detroit Locker 

Old 01-18-2012, 11:48 PM   #6
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Detroit Locker
Automatic Locker

The Detroit Locker has been around as long as there has been Jeeps. It was first made in 1941. Only then it was called the No-Spin and it was made by Tractech. The No-Spin name was used for almost 30 years. In larger trucks and commercial use this locker is still called a No-Spin. The Tractech company has since been acquired by the Eaton Corporation. The Eaton Detroit Locker is a very strong Locker. It does chirp the tires as you go around turns. The Detroit Locker will then unlock and lock again as you go around a turn. This does make it a somewhat noisy differential. It can even make people think there is something wrong with your jeep. In the mid '90s Eaton made changes to the Detroit Locker to make it quieter as it locks and unlocks. This improved Detroit Locker is called the SofLocker.

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Default Grizzly Locker 

Old 01-21-2012, 02:51 PM   #7
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Grizzly Locker
Automatic Locker

The Grizzly Locker is made by the Yukon gear company. It is a strong automatic locker similar to the Detroit Locker. The Grizzly Locker is available as a complete differential or a lunchbox locker (see the next post).
The Grizzly Locker is available for several axle models such as the Dana 30 but at the time of this writing it is not available for the AMC 20.


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Default Lunch Box Lockers 

Old 01-21-2012, 03:35 PM   #8
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Lunch Box Lockers

Lunch Box Lockers (sometimes called Drop-In Lockers) are locking differentials that can be installed into an existing differential carrier. This type of design greatly simplifies installation. There is no need to worry about gear meshing or the adjustments that go into installing an entire differential. A Lunch box locker can easily be installed by a shade tree mechanic. The disadvantage is the carrier is now the weak link. The carrier may have been strong enough for an open differential but a locker experiences higher forces and may fail after a lunch box locker has been installed.

Power Trax
This was the first lunch box locker manufactured. It has been sold since 1990. This locker has had several names over the years such as LA Locker, All-Track, Lock Right and Power Trax.



E-Z Locker
The E-Z Locker is a lunch box locker that was make from 1997 to 2008 but it has been discontinued.

E-Z Locker


Spartan Locker
The Spartan Locker is similar to the Lock Right Locker but has been designed to be be easier to install and remove than other lunch box lockers.

Spartan Locker


Lock Right Locker
The Lock Right Locker has been made since 1993. The Lokka is a similar lunchbox locker sold in Australia.

Lock Right Locker
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Default ARB Air Locker 

Old 01-21-2012, 10:29 PM   #9
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ARB Air Locker
Selectable Locking Differential

The ARB Air Locker was the first selectable locker. It was first released in 1987. It uses compressed air. The differential housing needs to be drilled and tapped to accommodate an air fitting. Inside the differential housing a copper tube brings air to an air cylinder that slides a locking mechanism to make the two axle shafts turn in unison. For an air sorce you ARB makes an air compressor that fits under the hood. This small air compressor is not the best to fill tires so some people will install a larger air compressor and fittings to fill tires too.
The driver usually has two electrical switches. One to turn on the compressor. This should be activated before the locker is needed. Then there is a 2nd switch to apply air to the locker.


ARB Air Locker in an AMC 20 Rear End
Mark King's photo from ausjeepoffroad.com
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Default Eaton E-Locker 

Old 01-21-2012, 10:55 PM   #10
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Eaton E-Locker
Selectable Locker

The Eaton E-Locker is an electrically activated selectable locking differential. A dash mounted switch will activate an electromagnet that will lock this differential.
The E-Locker is available for several differentials such as the Dana 30 but at the time of this writing is not available for the AMC 20 rear end.


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