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Differential Lockers: All You Need to Know!

Differential Lockers: All You Need to Know!


What the heck are Differential Lockers? Do I need em? Are you considering an after market diff lock kit (differential lockers)? Maybe you are looking at Toyota FJ80 and wondering whether to wait for the edition with the diff locks. Do you already have diff locks and want to know what they actually do!

I’ve used my stock diff locks for a couple years and I’ll tell you what I know! First, lets talk about a practical example.

A True Story:difflock

One fine day yours truly was feeling the call and headed out with a couple of buddies outside of Bishop, CA. We checked out the Cerro Gordo Mining Ghost Town and heard of a great trek up the mountain perfectly suited for rigs, “such as mine”. It was pretty easy going, though a steep climb, and it started to get interesting when we looked out the passenger window and noted the clouds and birds were below us. Now, my friend is married, so I know he’s a very brave man. He looked out the window and said quite calmly, “I don’t like this”. The rig was climbing steep, already in four low, kicking gravel into the thin-air abyss. I’m quite convinced those pebbles made diamonds when they finally struck the ground hours later. Just then, the rear tires found some soft ground, and dug in while sliding TOWARD the cliff. Buzzards circled. Waiting. If you’ve never actually had your stomach in your throat, you may not know it makes it impossible to speak. We were all quite certain one tire was hanging over the side, but all afraid to look. None of us speaking. One foot on the brake, I gave the 80 a little gas. That was a mistake. It dug in further, sliding toward the cliff. Now we were quite certain one tire was spinning freely dropping aspiring diamonds from its treads. I was petrified in my seat remained calm, not looking at my friends, saving them from embarrassment if they had messed themselves. With two feet on the brake peddle trying very hard to shove it through the floorboard, I slowly reached up and engaged the diff locks. “Ah heck” I thought (very calmly and not panicked at all), “I may as well lock-em all up, front, center, rear”.


254I turned the nob and heard what sounded like a 200-person choir. Two light “clicks” as the lockers engaged. Now, the diff lock lights don’t come on in an FJ80 unless they are engaged. Sometimes that takes a little movement. In this case, both lights came on, confirming we were locked all the way around.


Mustering my courage, I took ONE foot off the brake and eased on the throttle with the other. It was as if someone had replaced the dusty trail of gravel and stone with a stretch of the Laguna Seca Raceway. The 80 simple drove forward. No slipping. No wheel spin. We only drove 10 feet before we all wanted to stop and get out. Closer inspection showed our front tires were on solid rock, and our rear tires were in gravel. Loves me some diff locks. Now, as I recall this little tale, it reminds me of an overland principle I did not follow, “When in doubt, get out”. This is a principle my Wife is much better at following.

So, you probably guessed, I am a fan of diff locks. When it gets “real” there is no substitute, and it becomes clear if you understand how standard four wheel drive works. I’m not going to discuss 2WD (two wheel drive), because, who cares. Let’s review the basics.

  1. Standard Four Wheel Drive: With standard four wheel drive, the front axle is simply connected to the drive-train (engaged) to provide power to the front wheels. Now, all four wheels are driven. Three differentials still allow all four wheels to spin independently. However, when traction becomes an issue, the engine power will go to the wheel with the least amount of traction (wheel spin). From this point on, none of these options are available with standard four wheel drive! 
  2.  Four Wheel Drive Low (FJ80 Specific): In a Land Cruiser FJ80, when four wheel drive low is selected the center differential is locked. This means equal power will be driven to the front and rear axle NO MATTER WHAT. If BOTH wheels on EITHER the front OR rear axle have traction, the vehicle will move forward. However, if only one wheel on the front AND one wheel on the back have traction, you get wheel spin. You would see a tire on the front and a tire on the back spinning (happens more often than you might think).
  3. Front or Rear Differential Locked: Now it gets real. If you lock the front differential, and the center differential, not only does equal power go to the front and rear axle, but BOTH front wheels MUST turn at the same rate as the rear axle. Now, if both rear wheels have traction and one front wheel has traction, the vehicle will move forward. However, if both front wheels lose traction, and one rear wheel loses traction, wheel spin. You can see the chances of wheel spin diminishing.
  4. Front and Rear Locked: Now, with the center, front and rear differential locked, all four wheels MUST spin at the same time. Now, if only one wheel has traction, the truck will move forward. However, if all four wheels lose traction, wheel spin. At this point, its jack and winch time.

Fully locked differential:


If all four wheels lose traction at the same time, or you are so pinned that the full power of your engine will not rotate the tires, it’s jack and winch time (subject for another article).

Another True Story:

With a different crew, I approached a rock wall that obscured the entire front view. My friends thought I was kidding when I approached the wall without much thought, “We are NOT going up that”. I reached over, locked her up, and proceeded to climb the wall without pausing. No problem.

Caution: There is no faster way to bust up your transmission and drive train than fully locking your rig and trying to go up switchbacks on a concrete road. When fully locked, drive straight and slow. Also, if you are really stuck and your wheels will not turn, its time for a new tactic. Do not keep punching the gas!

If you want to have reliable transportation in any trail condition, seriously consider differential lockers!

Here’s a little video demonstrating a few points above.