While the Limited Slip Differential (LSD) has some great advantages, there are a few disadvantages that make this type of differential a loser in the books of hardcore off-roaders. Sometimes, you need to have an instant lock and that means you need one of two other types of differentials: a Locker or a Spooled Differential.

Again, the goal of a differential is to allow the driven tires to rotate at different speeds during turns. This prevents the inside axle from slipping, damaging the tire, and even potentially breaking the axle during a turn. This is great on a surface that has perfect traction all the time, but we’re on the dirt. Traction is practically optional. Can’t we get away with spinning both tires at the same speed during a turn on the dirt? Yes, we can but if you drive on-road even a little bit, a solidly locked up axle is still not a great idea. So, how do we continue to compromise towards something that works best off-road? That’s where the locker comes into play.

 

Lockers

While some LSDs do work off-road, the problem is they still allow for wheel slippage, especially when one wheel is in the air and the other is on the ground. While there are work arounds, those aren’t for everyone. In that case, you’ll want to look at a locker. Just with LSDs, there are different types of lockers on the market.

 

Mechanical Lockers

One of the more popular lockers owners install is the mechanical locker. The first one that showed up with made by Warn in 1973, but it was a short-lived design. It used roller clutch, so it was probably based on much of what they learned from their Lock-O-Matic hubs.

 

This type of locker needs no input by the driver and will remain in a “locked” state where both wheels will move as one whole unit. Until the side gears begins its camming action to push on the driver housing gears and separate it from the driver housing, there is no differential action. This type includes the legendary Eaton “Detroit Locker” and the newer Yukon Gear and Axle “Spartan Locker.”

Mechanical lockers can range from a unit that fully replaces the differential carrier to a drop-in unit that replaces just the spider gears of an open differential. Some drop-ins even reuse the side gears in their design to not only make it an economical choice but one that isn’t dependent on axle spline count since the axles are still retained by the side gears.

 

Automatic? Lunchbox?

Some will call this an “automatic mechanical,” “automatic,” or “automatic unlocking” locker because it’s locked until the outside side housing cams open and moves away from the center housing, thus allowing the outside wheel to rotate faster while driving the inside axle. The other common name for the drop-in mechanical locker is the “Lunch Box Locker” (named so because it has the look of an old-school, dome-top lunch box) or the “pocket locker.”

What either version has in common is their basic design. The housings (both sides and drivers) have toothed faces on them. This is what prevents the wheels from spinning at different speeds and is the locking mechanism of the mechanical locker. The driver housing is held in place with the carrier housing and a pin (or even a pair of pins), no matter if the entire unit is replaced or just the spider gears. The pins drive the center housing as they are locked in place with the carrier.

 

The side gears are moved by the axles and are separated from the driver housing when there is enough of a differential in speed between the axles. This allows the faster axle to cam open against its spring and collapse it. That is, until the side and driver housings reach equal speed again and the spring forces them together.

Again, this can range from a whole piece that directly attaches to the axle splines or contacts the original side gears of the open differential. Some lockers will also reuse the side gear thrust washers while others will not. If you are wondering, yes, this will make a “clacking” or “ratcheting” noise as the vehicle turns.

 

The “Gov-Lock” Locker

There is a differential locker that is truly automatic and acts only where there is a difference in speed between the two tires. This is known as the “Gov-lock,” used famously in many GM differentials with the G80 order code and made by Eaton. The “Gov” part comes from how it works. It uses a governor to reduce wheel speed of the tire with the least amount of traction.

 

First, it detects wheel speed difference – usually around a 120-RPM difference – by use of a centrifugal pawl mechanism that’s rotated by the cam plate. Then, then cam plate rotates with the cam-faced side gear and it forces the cam plate and other side gear against the clutch pack. Its pawls spread out and moves until it contacts the latch.

Finally, the latch engages and prevents the cam plate from rotating, which forces the cam faced side gear to rotate against the cam plate. This pushes against the clutch packs and locks the differential. It’s nearly instantaneous but it does have its limits. The weakness of this differential is mostly in its centrifugal pawl mechanism and latch.

 

If they make hard impact instead of a smooth one, it can cause one or both parts to break. Like, for example, if you’re driving normally and slam on the throttle of a high-torque vehicle, it’s probably going to break it before you break traction. On your regular, unmodified Silverado or classic, restored K5 Blazer, you will probably never have that happen.

If you’re building a truck to go hard core crawling or want to show off that new supercharger by slamming down on the throttle and spinning the tires (which you shouldn’t do on the street), you’re probably going to break it.

 

The other is that, while it uses clutch packs, it doesn’t use gear oil with friction modifiers for limited slip differentials. It uses GM part number 89021669 GL5-rated 80W-90 gear oil as most any open differential GM vehicle will use. Eaton even recommends Texaco 2276. a GL5-rated 75W-90 without additives as an alternative and the same fluid as the GM 88900401. There are two problems with both of those: Texaco 2276 is exceedingly difficult to find, and GM 88900401 can be quite expensive.

A 2276 alternative would be Havoline 222271 80W-90 (proper weight as GM requires) or Delo 2230319 75W-90 (a weight that Eaton recommends). They are both made by Chevron, who owns Texaco, and GL5-rated.

 

However, while they stress that it must be GL5-rated, even Eaton says that the clutch engagement isn’t enough to overheat the oil nor require a friction modifier additive like a limited slip requires. If you do use limited slip or E500 rated lube, there is the risk of glazing the clutches and the locking action will no longer work as the clutches slip instead of lock up.

Some people have and will use gear oil with friction modifiers in them in their G80 code GM differentials. While a few don’t report problems, a GM bulletin on the G80 equipped vehicles states that this can cause chattering while turning from a stop as the clutches are glazed over.

 

The corrective action is to drain the fluid and refill with the non-additive, GL5-rated 80W-90 gear oil or GM’s 89021669 until the problem goes away. This may happen in one change or several. However, there is the chance that the clutches may be too glazed over and require replacement. If after three changes, you’ll probably want to take it apart or have a differential technician do so instead.

So, for that reason we’ll also recommend that you don’t use gear oil with a friction additive (either made into its additive package or you add it to it) in your G80 equipped GM truck. Use GL5-rated gear oils only in the MLocker/Gov-Locker G80.

 

Driving With A Locker

The way a locker works can also make driving a bit of a challenge. As you go through a corner with no power, the axle differentiates like an open one. However, it will begin to drive both axles as they achieve equal speed to lock together again as either the inside tire slips more as you accelerate out of the corner or the outside tire slows down to match the inside tire’s speed. This can cause erratic behavior during cornering or even cause the vehicle to “push” towards the outside of the corner under heavy acceleration at mid-corner to exit.

 

Selectable Lockers

Until the 1980s, there were only two ways to spin the wheels of a 4WD vehicle. In the rear, you used an LSD or a mechanical locker. For the front, you were limited to staying with an open differential, a LSD in rare cases, or using a mechanical locker with a set of selectable hub locks if you happened to make a custom front axle out of a Wagoneer Dana 44 and a Jeep Dana 27.

Selectable lockers come in three flavors, if you will, in the forms of cable-pull, air-lockers, and electronic lockers. What separates them from mechanical lockers is the ability to select if they are locked or unlocked by the driver versus the “automatic unlocking” of the differential.

This means you can get the ability to lock up the axle so that both wheels spin at the same speed and torque but unlock them when you want to keep the ability to differentiate the axles for turning. It’s selectable by the driver and needs their direct input to work.

Nearly all of them use a form of a collar that moves to lock to a ring on one of the side gears in the differential. This locks the differential action and forces both wheels to move at the same speed and torque. How that engagement is done is what separates them from each other.

 

Air Locker

The original air locker was created by Tony Roberts in Australia with the “The Roberts Diff Lock” in 1982. He was an avid trail driver and off-roader that worked on the concept in early- to mid-1980. Originally, it used on vacuum until he finally hit on the right combination of parts and used compressed air operation. By 1987, ARB (which stands for Anthony Ronald Brown, the founder of the company that started in 1975) found the design and purchased it from Roberts and renamed to the “ARB Air Locker.”

 

Air Lockers need an air source to run and most people use an on-board air compressor with a small tank to store the air used for the lockers. In some cases, the compressor is enough, but will be running at a 100-percent duty cycle instead of just on demand.

 

You also gain the advantage of being able to use the compressor system for other uses like pumping air into your tires or other uses where you need to use air. However, it also means it comes with extra complication and cost over mechanical or even other types of selectable lockers.

 

Cable-Pull

The cable-pull locker is the most recent creation, in terms of when it came around. It’s essentially the same idea but instead of using air, it’s using your own pulling strength to engage the locker. So long as the teeth are lined up it will engage easily and not require an insane amount of strength. If it doesn’t want to move, roll the vehicle forward a bit and it will engage on the next tooth.

 

The advantage is in its reliability. There isn’t an air compressor to stop running, an air tank to leak down and empty, or anything else that would prevent you from engaging the locker outside of a cable breakage. However, thanks to modern designs, a lot of those advantages are reduced. There is one advantage a cable-pull will have over most selectable lockers: cost.

At even its most expensive, a cable pull locker will be between $300 and $1000 cheaper (or sometimes more) than a well-equipped air locker (well-equipped meaning air lines, pump, and tank). The only selectable locker that gets close to beating that price is an e-locker, which we’ll detail next.

 

Electronic Locker

The electronic locker, referred to as an e-locker, is the next newest in the development of the selectable locker. As the name implies, it does not use air or cables to engage the locker. Instead, the locker is engaged by sending vehicle electrical power to a stator – an electromagnetic coil – that pushes a set of pins into one of the side gears. This locks the axle and sends full torque to both wheels, just like the air locker.

 

Auburn’s ECTED Max

Auburn Gear’s version of the e-locker, the ECTED Max – which stands for Electronically Controlled Traction Enhancing Differential and pronounced “ek-ted” – is the best of an LSD and a Locker. Instead of defaulting to an open differential, it has a limited slip clutch pack is used on one of the side gears.

 

As the differential works to control the traction difference between the wheels, it forces the side gears to push out and squeeze on the clutch pack. Once that happens, it begins to transfer torque to the wheel with more traction just like a LSD.

However, when you flip the switch, the coil is engaged and pulls on the pilot cone. The coil also spins on its own bearing, so it never rotates with the differential case. This allows a set of ball bearings on the other side gear to ride up a ramp and force the side gears to put against the clutch pack.

 

This effectively turns it into a spool and locks both sides of the axle together just like a traditional locker. Unlike other selectable lockers – even other e-lockers – the ECTED can be engaged at most speeds. It also means that the ECTED’s operation is far quieter.

The problem, though, is that it is a clutched LSD. It requires a break-in period for the clutch pack, special fluid to ensure the pack has proper friction, and frictions and plates that will eventually wear out in time. Fortunately, these parts – from the clutches to the coil assembly – can be replaced by the end user but there is also Auburn’s D-REX – the Differential-Replacement Exchange – program.

This does require you to send the entire unit out to and the unit must not be older than 4 years from your purchase date to qualify. You also need to get a Replacement Exchange Number from Auburn before sending your differential unit in or else it will get sent back to you.

 

Spools

Spools are simple ways to connect the axles together. Even so, there are still two distinct types of spools: Full Spools and Mini-Spools. It’s not that they operate differently between each other, it’s how they are installed.

Since they are both the same, we should talk about how a spool works. Again, it’s simple because all it does is permanently locks the axles together. There are no clutches, no springs, no electronics – it’s a single or three pieces of metal locked together in the differential.

 

Because they are permanently locked, there is no differential action when the axle goes into a turn. The benefit is that you’re always supplying power to the axle that has traction. The problem is that you no longer have full control as you turn your vehicle because both tires will try to spin at the same speed.

This can cause a vehicle to increase tire wear, increase the possibility of damaging an axle while driving on asphalt, or cause the vehicle to understeer (oval track racers would call this a “tight” condition as the front end heads toward the wall).

 

Mini-Spool

A mini-spool is the easiest version to install of the two as it doesn’t require you to remove the entire differential. You pull the center pin, remove the C-clips on rear ends that use those for axle retention, drop out the spider gears, and install the mini-spool in its place.

If you have a rear end where the axle is retained by bolting to the bearing housing (like the Ford 9-inch, Toyota 7- and 8-inch, Nissan H233B, Suzuki Samurai rear axle and many others), they don’t need to have C-clips but will retain the pin(s) of the spider gears. This is because the axles need to be pulled out to drop the front mounted carrier. These don’t have a cover to access like C-clip axles and you’d never be able to install the carrier or the axles (let alone remove them) if they didn’t.

 

For the Chevrolet 14-bolt and Dana 60 with posi-traction and their four-pin carrier, it’s slightly different. Since its spider gear pins are made from a single piece of cast iron, its mini-spool replaces that entire assembly. It also is the more difficult of the mini-spool applications. It requires the entire differential to be removed from the housing and split the carrier open to access the spider gears. If you’re worried your open differential 14-, 10- and 12-bolt GM and smaller Dana rear ends are the same, don’t worry, they aren’t. They are standard open differentials.

 

The disadvantage to the mini-spool – outside of being a spool – is its size and that most are made from multiple pieces. Both combined can make a poorly engineered or formed mini-spool easy to break. This is especially true for vehicles with over 350-horsepower, grippy tires, and a high-traction surface.

 

Full Spool

A full spool is a single piece that replaces the entire differential carrier with a single piece of metal that attaches to the ring gear and the axles. For axles the use C-clips, you’ll also need to buy and have C-clip eliminators installed. These turn c-clip retained axles into bearing housing retained axles like front-drop carrier axles. However, this does require machining, some possible fabrication, and pressing on bearing retainers to make this work.

 

While you still need to remove the ring gear and differential, the full spool of the front-drop carriers and posi-traction GM 14-bolt and Dana 60 axles is a bit easier since it doesn’t require any further modification. Since they have no C-clips to worry with, they don’t need the conversion.

 

The advantage to a full spool is its strength and weight reduction when compared to both the mini-spool and any differential. Since it’s made of a single piece of metal, it can be machined to reduce its overall weight or even made of a lighter but stronger metal. The down side is installation difficulty can vary from needing to possibly needing to re-shim your ring and pinion to full on fabrication to install C-clip eliminators.

 

Super Cheap

If the cost of a full-spool, LSD, Locker, or even mini-spool turn you off, there is another option. It’s lovingly and sarcastically named the “Lincoln Locker,” or the “Miller Locker,” or whatever your welding machine is branded as. Yes, the cheapest way to lock your axles together is to weld the spider gears to each other, to the case, or all of the above and never be allowed to move again.

 

And, for the love of Pete, no. IT DOES NOT MEAN WELDING THE RING GEAR TO THE PINION GEAR. That’s not even the differential. Yes, we realize this was done as a meme-type joke, but still. If you don’t know what someone means by “welded diff” and this is what you’re thinking, it’s probably a sign that you shouldn’t be messing with your differential or entire vehicle, at all.

By “Lincoln Locking” your differential, it’s been converted into a solid piece. You’ll get full spool advantages and disadvantages without spending the money for it. A full spool isn’t typically that expensive at under $200, but welding wire and time are cheaper than that.

 

Another version of this we’ve seen and really like is the “Fozzy Locker.” Instead of permanently and irreversibly welding the spider gears together or to the case, the Fozzy method welds the teeth of the side gears except for where they meet the pinion gears. In some cases, all four spider gears have their teeth filled in except for where they meet.

 

This means you can go from a locked differential to an unlocked one by just replacing the spider gears. It makes this as reversible and easy to install as the mini-spool without the cost of the spool. Well, we suppose that’s depending from one’s point of view. If you don’t know how to weld, you’ll need to hire a welder or pay your welding buddy in a suitcase of beer. So, there is a cost but it’s not as high as a mini-spool, even as inexpensive as that is. Most mini-spools are under $100 and, again, welding wire and time are typically cheaper than that.

 

The other downside is that the strength of the lock is totally dependent on your welds on both cases. Weak welds can break apart and destroy a fully welded differential. A Fozzy locker could break the welds from the filled in teeth as the gears try to move and mesh together. A correct process and preparation can prevent this from happening, so you need to be sure your welder (or you) knows how to weld the type of metal the spiders and carrier are made of. This is especially true of cast iron, which must be brought up to temperature prior to welding.

 

Ok, Which One?

In most vehicle modifications, we always try to steer towards “it depends on its use” because it nearly always does. In this case, since most of you will be driving on- and off-road, we’re going to recommend an air or cable selectable locker. While they aren’t the easiest to install, they will always allow you to have differential action when they aren’t activated and fully-locked when they are. It gives you the true “best of both worlds” case.

 

A close second would be an electronic selectable rear, specifically the Auburn ECTED Max, and a either a selectable front differential. Since it gives you a limited slip differential when inactive, this is an excellent choice for the rear of the vehicle. When you need both axles to be powered, the front will remain an open differential and easy to turn. When you need all four wheels to turn no matter the conditions, hit the locker buttons and send equal torque to all four.

 

So, this is a bit of an unusual case where we can recommend something as it’s something that needs to work specifically for both on- and off-road. You only get that with a locker you can select as on or off. Can you off-road with a LSD, welded diff, spooled diff, auto-locking diff, or even an open dif? Yes, you can. However, the disadvantages of those differentials weigh heavily out of their favor when compared to the advantages of a selectable locker. Selectable lockers can be quieter, more reliable, and won’t stop working when a wheel is up in the air when they are engaged.

 

For those reasons, we’ll always recommend the selectable locker when there is a budget for it in a build. Automatic lockers would come next and then LSDs. We’d only come close to recommending spooled differentials in a full racing application. We’d stay away from welded if you can as they can be destructive, they could fail spectacularly if done wrong, and honestly a mini-spool isn’t that much more expensive than hiring a welder.

 

Fortunately, we have products from Eaton, ARB, Alloy USA and our online catalog is always expanding to include more in our physical and online stores. We even offer covers, replacement parts, bearings and more for your installation needs!