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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:

imagesCA63GK7I

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.

 

Michael

Backwoods country bumpkin. Overland enthusiast and lover of the great outdoors.

Comment(0)

  1. A couple things to add about diff-locks:
    1. You cannot lock the front diff by itself.
    2. You should avoid locking the front diffs as it puts a great strain on the differential. It should only be locked in soft mud and NEVER on rock or hard ground.
    3. If the front diff is locked the front wheels should be straight as possible to avoid breaking the birfield bearing cage. For some reason (at least on the 80 Series) torquing up the front wheels while the wheels are fully turned will snap a the bearing cage quite easily.
    4. Always try the rear diff lock before engaging the front to avoid damage to your front axles. Avoid wheels spin for maximum traction.

    Well thats about it. New Member here.
    Regards
    MUDZLLA
    HDJ80-VX Limited

  2. Great article.

    You may want to place some added emphasis on the applicability of the center diff to Toyota/Land Rover/AWD products, whereas most select-able (I hear you NP203 crowd) 4WD, not AWD, transfer cases do not have a center diff, where engaging 4WD gives direct drive to the front and rear transfer case outputs.

  3. Michael… Nice web site. You are “doing the deed” so to speak. Hats off to you! Regarding information on differential lockers, great start with this small bit of information for your readers. I would however, not title this small article: “All You Need to Know.” So as not to mislead readers, in my humble opinion, I’d rename this piece: “Lockers: A Primer.” There is LOTS more to know about lockers than what is covered here – how they actually work, how/when to use them, automatic vs. selectable, locker “creep” on side hills (very dangerous), how to use lockers in conjunction WITH other traction aiding devices, like electronic traction control and even airing down to a lower psi. They also need to know which traction aiding devices to use first, second, third, etc. until you get unstuck – lockers should not typically be your first choice. While teaching corporate, government, and recreational off-roading through my training company, Off-Road Safety Academy (DiscoverOffroading.com), I’ve found that many folks don’t even know how a differential works, and what an “open” differential means. Until they know how differentials function, they will never have a clear understanding of lockers. To really understand differentials, watch this marvelous 1937 Jam Handy film: https://www.youtube.com/watch?v=67XoCMTcN7M. After watching this short film and listening to the overview of differentials in my courses, I’ve had differential repair mechanics say, “Hey, I never really understood differentials until today.” I’ve also found that many recreational off-roaders use lockers inappropriately (and way too quickly), as a cure-all for poor driving skills (as your short piece on lockers suggests). Again, nice piece… Keep doing the deed and trying to educate. Education good; ignorance bad.

  4. Once again, another very, very good article, and I concur with Robert. I have witnessed more than a couple of guys that really didn’t understand when to use and when not to use lockers.. It makes me cringe, much like fingernails on a chalk-board, when I hear rears chirping away on slick-rock when cornering.. I’ll also add that I just wouldn’t even consider having a vehicle without at least a rear dif locker. I very rarely use the front.. According to the the 80 series/450 owners manual, one should never have the front locker engaged while in reverse. Serious damage may be incurred..

  5. This is a great article! Now, though I have a “Trail Rated” Grand Cherokee – with the Hemi, of course 😀 – I don’t get into many places requiring “heavy duty” 4 wheel, but I am trying to learn it so that I can understand what I’ve got, what I need in the event I ever get into a position of, well, as Michael stated in his article, remaining calm in my seat.

    On my Jeep, I have a little switch that flips on a motor that puts my transfer case into 4-Low. And when it is in 4-Low, it’s a beast! It just wants to crawl all over.

    Just after buying this vehicle, I was trying the 4-Low. I was in a parking lot that had a steep hill up out of it – dirt – which then flattened out. Put in drive and took my foot off brake and with no gas applied to pedal, Jeep crawled right over parking barrier – about 6″ high – and right up the hill like nothing was even there. When slope flattened, I turned wheels at which time it shook and churned. Immediately I turned back to straight and realized it was 4WD mechanism. Called dealer and they said to not turn the wheels when in 4-Low. Would this be indicator that switching to 4-Low on this vehicle triggers a diff lock like system?

    All this stuff is making me pull my hair out … which is no small feat considering what’s left of it!

    1. Hi @Lassen10463 I’m going to put you in touch with another Jeep Owner who is very active in our forums. Perhaps @ShawnR can give you some specific advice on that particular behavior, and what it means for a Jeep. Also consider heading over to our forums and asking if you haven’t already. To me, “Don’t turn” in 4-low seems extreme, though if you were fully locked, could describe the behavior you experienced.

  6. I’m not much of a gear head but I do know that if your on dry pavement or surface and using 4 low, you’re going to get binding when turning. I have QD2 in my Grand Cherokee and only used 4 low once in some deep snow. I have LSD front and rear, no lockers. Anyway, using 4 low on a dry surface with all 4 wheels on the ground, etc, is not optimal. I’ve never attempted to see how far I could turn my wheels when in 4 low but now I’ll have to find some mud and try it. I had always been taught that never to engage 4×4, such as on my Wrangler while on a dry surface, especially concrete as it can wear parts out faster. On a trail, that’s a different story. If you head over to the OB forum you’ll probably get more info from people with a lot more knowledge than I have. Good group over there with lots of knowledge.

      1. Thanks, Shawn! Like you, I rarely have needed “crawler mode” but I do like knowing I’ve got it…just in case! In the meantime, there are thousands upon thousands of miles of dirt/mud/rocky/sandy/powdery roads in CA alone I have yet to explore. What’s that line in one of the Pirates of the Caribbean movies…”You have to get good and lost before you can get to where you’ve never been.”

  7. Just this year it has become necessary to drive my 2006 Rubicon on a mile long hilly, winding, unmaintained road in Maine. Sometimes (like now) that road gets completely iced over. No snow, just ice.
    Questions: 1) I’ve been engaging Front and Rear Lockers the entire length, and getting by so far going very slowly. Am I damaging anything mechanically?
    2) l considering some kind of tire chain or cable. Any suggestions?
    Great forum,
    Thanks!

  8. Just this year it has become necessary to drive my 2006 Rubicon on a mile long hilly, winding, unmaintained road in Maine. Sometimes (like now) that road gets completely iced over. No snow, just ice.
    Questions: 1) I’ve been engaging Front and Rear Lockers the entire length, and getting by so far going very slowly. Am I damaging anything mechanically?
    2) l am considering some kind of tire chain or cable. Any suggestions?
    Great forum,
    Thanks!

  9. Michael, nice article. I would like to add that lockers can be dangerous in off-camber situations, the back will crab out causing the vehicle to come off its line which could lead to a roll over. You will rarely see front lockers with IFS vehicles , too much stress.

    Lockers should be considered a luxury and used sparingly, they tend to tear up trails. I would recommend people take a good I4WDTA 4wd 101 course to learn left-foot braking, two peddle driving . By applying the brake the driver can build up enough RPMs (without moving) to force both wheels to spin when the brake is finally released. This can be done so smoothly by skilled drivers that a bystander would assume they had lockers.

  10. This is a really nice article, but what diff lock would you recommend for a dune buggy using a newer version Jetta or golf engine in a midship rwd configuration?
    Greetings from Canada

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