Unlocking the Truth Behind Automatic Lockers

Here is the deal. Whenever there seems to be growth in a segment of the aftermarket world whether it is the street world, off road world, even the race world, not long after a product reaches the end users the rumors start. Some of these rumors are based on truth, some are based on end user error, some of them are based in hypothetic knowledge vs. direct knowledge, most rumors are based in the never ending side talk focused on “us vs. them” with no practical knowledge to begin with.  The debate about Automatic Lockers is nothing new, since almost the inception of the Locker, the conversation for and against the Locker has been had around many a campfire, barstool or garage talk. This article is going to move some of that conversation out of the myths and into the facts and personal experience.

Anatomy of a Detroit Locker

Anatomy of a Detroit Locker

FACT: An Automatic Locking differential is a differential where the coupler gears of the left and right axle shafts are locked together in unison as power is applied to the axle through the pinion gear. The “Locking” Mechanism is normally a center section of the differential, most commonly called driver gears or a driver assembly that are placed under spring tension. The Pressure from springs forces these driver gears into the side coupler gears making the whole axle turn together at the same speed.

Pros of an Automatic Locker- Because a locked axle turns together in unison and there is no slip between the left or right tire, the tires are actually receiving 100% of the power being sent to the axle. Other traction devices such as Posi-Traction or Limited-Slip Designs at most can transfer only 65%-70% of the power given to them to the ground. If you have ever had the chance to experience the difference, it is absurd. A locking diff vs. a Limited slip diff is more than noticeable, it can make a driver laugh hysterically while stating terms of invincibility as they idle over previously challenging obstacles. 

Most commonly in some gear driven limited slips, the differential has to allow one tire to slip, causing a ratcheting effect in the differential which transfers power to the other side. This slippage equates to loss of power and to loss of momentum as the differential transfers power. With Posi-Traction differentials which instead of gears inside have clutches, this differentials has no “ratcheting effect”, instead power is transferred between each wheel through the use of a clutch pack. The inherent problem with clutches is that “slippage” between axles equates again, to a loss in power. This is why in this aspect a locker has zero mechanic slip and therefore transfers 100% of the power it is given.

These mechanical traits are only highlighted further with a locker when you start driving a vehicle with one. When driving a vehicle with a locker you start to notice certain things that are no longer happening when off road, like the fact you do not hear tires slip, you also will notice that you will not feel one tire break free and then transfer power to the other. With each tire turning together at the same RPM’s or Revolution Per Minute. There is noticeably less abuse on the whole drive train with a locker.

Cons of an Automatic Locker- Because the unit is “automatic” the driver cannot dictate how and the when the unit LOCKS or UNLOCKS. While there have been some wild accusations and urban legends of people flying off rainy roads, sliding through ice, and “lockers making vehicles wildly undrivable in poor conditions.” I would like to take time and ask….then why would anyone want them if they make a vehicle so uncontrollable to drive?  This is when the “no personal experience” keyboard warriors seem to come out in droves… I have driven an automatic locker in every terrain imaginable, fresh rain, down pours, sleet, snow, mud, sand, rock. About the biggest down fall of an automatic locker is they can chirp tires on pavement when making tight turns, they can make clunking or clicking noises making tight turns in parking lots and they can make a vehicle want to oversteer (Drift)  if you apply too much power in a low traction situation. The most common side effect of a locker is at times the differential will unlock and lock around a corner which can feel like a jostle in the cab.  Most common con thrown out on the forums aside from DEATH with an automatic locker is that with lots of street use an Automatic Locker will also cause your rear tires to wear “more” than without a locker (from the chirping, scrubbing of the slower moving tire through a turn.) There has been no research to my knowledge to prove just how much “more” tire wear that is. I am trying to document this through my daily driven RAM 2500, and so far…my tires are not melting away as suggested by the keyboard keepers of the off road realm. But more on this later.

Why would you want an Auto-locker?

Cold hard facts? First, an Auto-Locker is dirt cheap next to comparable selectable lockers like ARB, OX, Eaton E-Locker, etc. Just in hard parts for a Dana 80 rear end. An Automatic Locker can be had for about 700 dollars (lunch box lockers can be had for sub-$400’s) Where for the same unit from ARB, OX etc. with the needed compressor, Cables, levers, can quickly add up to 1500 dollars+. Thats firgure is just parts, we havent even talked about install. 2nd reason, the Auto-Locker design has been around since WWII,  95% of the Locker’s available today are damn near bomb proof. While almost every off road forum will tell you that its Toyota E-Lockers or ARB air lockers till the messiah returns, the fact is…You will never need an electrical relay or an air solenoid in the middle of the desert with an auto locker. With no need for any supporting modifications (air system, electrical wiring) an auto-locker always works. I own 2 rigs with lockers, one being my Jeep YJ with ARB’s front and rear and the other is my Trail Pig, a 99 Dodge Cummins 4x4 with a Lock Right in the rear. Only one has led me to modify an off road trip because a locker was not functioning properly. Hint: It was not the Lock Right. Double Hint: I love my ARB’s and would not change them for anything in my jeep. Wisdom to be learned? All things have a purpose when we understand INTENT. Back to the Automatic locker, the next point is maintenance.  Automatic Locker’s are like crockpot’s, set them and forget them. Air and Electronic selectable lockers have wires that can chafe, airlines that can crack, O-rings that can go bad in the units. Do not read that automatic Locker’s are infallible, but I have talked to a lot of Detroit and Yukon Grizzly owners and short of trying to be King of the Hammers, or throw 600 hp onto a rock face, automatic lockers have a very low fail rate in the wild. Normally what kills a locker is something else breaking and taking out the side gears in the locker.

So let’s sum this up again, Reason why an Auto locker would be appealing? Lower Cost of ownership than other Traction Devices (Electronic, Air, even some Limited Slip Diffs.) NO need for supporting mods (air tanks, compressors, electronic wiring.) Low Maintenance (No special oil additives, no clutch fibers to replace.)


Myth #1- Locker’s make your vehicle un-drivable on the street.

False*-  I use an asterisks because in the world of the interwebs, half truths become whole lies and the Forums (the meeting hubs of the largely uninformed) are divine instruction. I also want to walk through some of the exaggerations mentioned on the internet. This myth is one of the previously mentioned half truths perpetuated by many individuals with no direct knowledge or experience with a locker at all.

An automatic locker will not make your vehicle un-drivable for “daily driving” duties. I have one in my truck, I drive 400 miles a week in Orange County and LA. I park on narrow streets, I make U-Turns by the hour. I haven’t wanted to throw it all in the trash yet. Not once has the Locker tried to kill me (this has been disappointing.) People say an Automatic Locker behind a manual transmission will make your vehicle “change lanes” between shifts. WRONG, People say you will be followed constantly by, clanks and bangs and your vehicle jumping and jostling at every turn. Not ALWAYS true. Once you drive with a locker you learn how to drive WITH  a locker. Like any modification to a vehicle, you learn how to drive a vehicle differently. You have to adjust your driving when your vehicle is lifted from stock, why is it so much different when you upgrade something like your differential? Once you have a few days in your vehicle You learn how to add and remove power to get the differential to unlock. The only time the diff makes noise for me is when I am making U-turns or sharp turns in parking lots.  Another example is when making right and left turns from stoplights normally the only sound I hear is a tire chirp over a paint strip. Never have I felt the locker make my rig unsafe. 90% of the time I have no idea the locker is there. For those warming up the war drums, I have driven my own vehicle a ¾ ton Dodge Cummins and a Jeep XJ with Lock-Rights in the rear axles, both sticks, and both over at least 1000 miles. My experiences were the same. Yes a Locker in a heavier vehicle feels smoother because of the weight of that vehicle leveraging against the differential, but I never experienced the exaggerated symptoms I have heard about on the interwebs.

Myth #2- An automatic Locker causes increased tire wear

Half-Truth-  The logic behind this comes from the fact that since both rear tires are locked together one wheel has to “scrub, or chirp” to catch up to the faster moving tire. The logic is correct. This goes back to the “learning how to drive with a locker.” If I power through a turn, the differential locks up and I get the chirp. If I allow myself to cost through a corner, the differential unlocks and I do not chirp a tire, then no additional tire wear happens. However, once you have a locker installed…it seems some side effects of “hoonage” happens, which means….for a short while, most people like chirping tires around turns or the fact that your peg leg vehicle is now a drift ready metal missile. So sorta like the MPG message… your miles may vary just as much as how many drifts you would like to do….


Myth #3- An Automatic Locker in Snow Equals Automatic Death.

FALSE*- Almost always the first post after a, “Should I get a locker?” post is the race to be the first person to state that in the snow, “Your truck is going to immediately slide out of control.” So let’s take this one slowly. If you are the type of driver that would have killed yourself by now in life without traction control on every vehicle you have ever owned. I don’t have an answer for you. Stick to micro coffee brews and farmers markets. But I am going to assume that people CAN LEARN and can get progressively better at something. A vehicle with a locker in it on ice does require more focus to drive than one without, but interestingly enough, both vehicles are hard to drive, and if you are not focused on your driving in either vehicle, most likely your chances of a favorable ending to your adventure are not good. Driving a vehicle without any traction control or traction devices in the differential makes a vehicle constantly pull to whatever tire loses traction, where a vehicle with a locker will oversteer more in similar situations, normally pulling towards the direction of gravity. Oversteer is when the rear end of the vehicle wants to “physically pass” the front of the vehicle. Think drifting. Many people seem to forget that if you feel the rear end start to “step out “ or start to put the vehicle into a slide…. YOU CAN LET OFF THE GAS. Which will normally make the vehicle get back into line and solve that whole situation of an icy death. (again, certain off camber situations can get more interesting as again a locked vehicle will want to slide toward the direction of gravity.) But, NO, a locker will not make your vehicle un-drivable or unsafe in the snow.

 Even in my Wrangler which I have used for years as my go to snow machine, I have always left my ARB locked in my rear axle in some of the deepest snow situations I have ever been in and my vehicle has never acted out in a manner that made me unsafe. Even now with the Ram, I had the opportunity to drive on a very icy HWY 18 in Big Bear. The biggest thing I can recommend is driving at safe speeds and driving corners with the respect they deserve. I had 2 times in a 2 hour drive where the truck stepped out on me, both times all it took was rolling off the gas and rolling back on smoother.  For years ACROSS America, lockers have been used in snow plow rigs….if the MYTH of icy death was true….how the heck did Detroit sell so many for so long?

So in closing, I want to make one point 100% clear, YES, a Locker will make your vehicle feel different in certain situations. An Automatic Locker will be more noticeable during daily life than a selectable unit such as ARB, OX, Eaton, etc. With an automatic locker you will not want to take corners as fast in the rain, or ice, but you shouldn’t be Ricky racer in those situations anyways. Do I think that automatic lockers are for everyone? NO, if you are a super picky person, if you want your truck to drive like a Lexus, then an Automatic Locker is probably not for you. But if you are okay with wearing your jeans 2 days in a row and are 100% for instating the death penalty for Man buns, an automatic locker might be the right choice for you.

That’s my .02 cents