A Locking differential is an amazing piece of engineering if used correctly. This single drive-train component can mean the difference between a good off-road 4×4 vehicle and an excellent one. If you’ve ever driven off-road with a 4×4 that has a locking rear differential you will be able to relate to how easy it makes a vehicle overcome most obstacles. But what is a locking differential used for and when does one engage the locker? What is the difference between a rear locker and an LSD (Limited Slip Diff) To find the answer to these questions and more read on…
Differential lockers are used to overcome a limitation of an open differential in off-road conditions by locking the center, front or rear differential to distribute power and torque evenly to both sides of the diff. By locking a front or rear differential it allows the axle to turn both wheels simultaneously at the same speed irrespective of traction differences.
If you would like to know more about how a locking differential works and when it is appropriate to use, continue reading…
How does electronic locking differential work?
A locking differential or “lockers” as they are commonly referred to in off-road circles, essentially locks an open differential, may it be the center, front or rear diffs, and forces both axles to operate as one unit and turn at the exact same speed irrelevant of the traction or lack thereof. Unlike an open differential that allows both wheels to turn at different speeds especially when cornering, the diff locker forces the axles to rotate at the same speed and is only designed to be engaged once traction is limited or almost lost.
A locking differential is like a magic button that gives a vehicle a major advantage over an open diff especially under challenging driving conditions like rock crawling or deep loose ruts. Thick muddy conditions are also a perfect opportunity to engage rear or center diff lockers. Read: How to use 4WD properly – THE COMPLETE GUIDE
It is very important to note that locking differentials are only designed to be engaged under very extreme conditions. DO NOT ever engage a locker on the open road especially on bitumen (Tarmac) and if used incorrectly can cause major damage to expensive drive-train components.
Torque is always transferred to the wheels with the least resistance.
Not all 4×4 vehicles are equipped with a rear diff locker which means you will have to adjust your driving style to compensate for the lack thereof. A vehicle without a rear locking differential could possibly still overcome a difficult obstacle, it just means you will need to use more momentum to get your axles over the obstacle. Once any of the wheels become airborne, or you find yourself in a cross-axle situation, which often happens off-road, the torque will always be transferred to the wheel with the least resistance, resulting in a temporary immobile 4×4. If not enough momentum is used, you could find yourself stranded with your wheels spinning in the air.
Read more on: Can you drive in 4H on Dry Pavement – Highways
Open diff vehicles like the older Land Rover Defenders, Suzuki Jimny, and many other basic 4WD’s without any TC (Traction Control) and electronic systems will need more momentum and struggle a bit in cross-axle off-roading conditions. Read: How to use 4WD properly – THE COMPLETE GUIDE
Off-road Example:
If one wheel is in mud/sand/snow and the other is on the tarmac with good traction, the torque will always be transferred to the wheel with the least resistance i.e the wheel with the least traction. TC systems have been incorporated to overcome this “weakness”
So when would you engage a center differential locker? To find out, read further…
When To Use Center Diff Lock
A center diff locker (4H mode) makes for easier, safer, and more controlled driving in sand, mud, gravel, snow. Do you get the idea? Yes, whenever you venture off the tarmac it is time to engage that center diff locker. That is when you know, your adventure has officially begun. Most conventional 4×4 vehicles have 2H, 4H, and 4Lo gearbox options. This means you will almost always be in 2H when driving on the tarmac. 2H mode allows better fuel consumption and more even tire wear. When making turns the outer wheel of the turn always turns faster than the wheel on the inside. Think, track and field athletes running around an oval track with the runners starting off in the same line. Runners on the outside lane have to run faster to cover more ground to keep up with the runners on the inside lanes. To compensate for the corner, runners are placed in a staggered position to make the race fair.
Slippery Surfaces
Lock the center diff when the surface you are driving on gets slippery, like gravel roads or when there is ice or snow on the tarmac. Those driving conditions would be a perfect time to engage 4H, splitting the power between the front and rear driveshafts. This gives you improved handling and traction.
Difference between diff lock and 4×4 – When To Use Rear Diff Lock
Then rear differential lockers are engaged when you want to overcome an off-road obstacle slowly without any damage. With a rear differential locker engaged, you have improved control of the vehicle and less momentum is required since both rear wheels are locked as if it were one axle turning at the same speed irrespective if there is traction on either of them or not.
| Sand driving |
| With the rear locker engaged in deep soft sand, your vehicle should get out of a potentially immobile situation before you dig yourself in. Do not wait until you are completely bogged down to the axles before you engage the rear locker. If you feel the vehicle is struggling, stop the vehicle and immediately engage the lockers and watch it crawl out. |
| Driving uphill on a steep uneven surface. |
| Also, when driving uphill on an uneven surface you will definitely want to engage your rear differential locker rather than attempt the track with an open diff. Driving uphill on an uneven track with open diffs requires quite a bit of momentum if you hope to succeed and the risk of damaging your vehicle is increased substantially. You also risk damaging the off-road track and making the conditions worse for the vehicle coming through after you. |
| Driving downhill on uneven terrain |
| Here you only want to engage the rear differential locker because engaging front lockers limits your vehicle’s turning ability drastically. The rear locker is perfect in conjunction with engine compression braking. You will have near-perfect control of the vehicle. Rear locker engaged driving downhill also decreases your chances of slipping as traction is increased across the rear axles. |
| Crossing riverbeds with soft sand and slippery rocks |
| In this situation, you also want to avoid getting bogged down before you call on your locker to rescue you. Getting stuck in deep water, you risk all sorts of expensive electrical damage. So you really want to get in and out of deep water as quickly as possible. |
Manual vs Automatic Locking Differential
A manual differential lock means the differential is open by default. Once you manually engage the 4H mode then you close the center differential and power is split evenly across the 2 driveshafts. The same can be said about the front and rear differentials. Usually, they are open differentials and you need to manually close the rear or front diffs by flipping a switch and engaging an electronic differentials locker to close it. This closes the rear or front axles and makes them operate as one unit and not independently as before. Automatic locking diff is also known as an LSD or Limited Slip Diff.
Locking Differential vs Limited Slip Diff
An LSD can never compete or make a vehicle as capable as one with a rear diff locker. The LSD works by allowing a small amount of wheel spin and then automatically engages the LSD (Limited Slip Diff) Read: AWD vs 4WD – which is better
LSD (Limited Slip Diff)
LSD works by limiting the independence between right and left axles. The most common Limited Slip Diff technology is clutch-pack-based or pre-load spring-based. It consists of a series of friction and steel plates packed between the side gear and the casing.
This technology works by allowing the wheels to function normally on the tarmac and high traction surfaces without having to engage or disengage anything. The wheels are allowed to turn at different speeds like when taking corners but will lock up when driving in a straight line and the clutch pack or metal plates detects it is in a high-torque situation. The torque coming from the driveshaft then forces the diff closed. It sounds good in theory, however, it is not as effective as a differentials locker or even a modern TC system. It is, however, better than just an open differential.
Traction Control
Traction Control (TC) functions similarly to a differential locker accept it activates automatically once the vehicle senses the loss of traction. Most vehicles allow you to switch this function off as it can hinder the forward progression quite a bit, especially in sand. TC works by detecting loss of traction on the wheels via sensors and then automatically applies the brakes only to the wheels that have lost traction thereby sending more power and torque to the wheel with the most traction. It functions similar to a manual mechanical differentials locker but not quite the same as there is still a small amount of traction lost first and wheel spinning necessary before the TC is automatically activated. It also hinders the vehicle’s capability in certain off-road conditions.
Conclusion
Your locking differentials are there to prevent you from getting stuck in the first place by overcoming the off-road limitation of an open differential in challenging driving conditions or cross-axle terrain. This is accomplished by locking the differential to distribute power and torque evenly to both sides of the diff. Use your differential lockers wisely to protect your vehicle, the off-road track as well as the environment.
Happy 4 Wheeling and remember, Safety First!!!