Automatic Lockers are a simple and effective way of gaining extra traction needed when driving off road. The internals whilst varying slightly between models, work on the principle of 2 bi directional dog clutches which lock both axles together when torque is applied and unlock when one wheel is required to spin faster than the other, such as when the vehicle is cornering, however they will never allow one wheel to spin slower than the differential center.
Below is a video from Yukon Gear showing the operation of their Grizzly Locker.
There are essentially two different types of Automatic locker on the market, the drop in style locker which fits inside your factory open center, or the full carrier locker which replaces the center entirely. Let’s have a look at these in a bit more detail.
Drop In Locker
Simple, cheap and effective traction. Drop in Lockers have been around for ages. As you can see by the above picture, they simply drop inside your existing open centre. In some models the locker components replace the existing side gears and others they retain the existing side gears, however the principle of operation is the same.
Advantages of the drop in locker include:
- Ease of fitment. Most can be fitted by the home mechanic.
- Price. They are significantly cheaper than a full carrier locker as there is a lot less material.
Disadvantages of the drop in locker include:
- Strength. Whilst the internal components of some newer designs of the drop in locker are very strong, the differential is only going to be as strong as the stock open carrier itself, which can vary greatly over some model vehicles. Lucky for the Toyota guys the stock open center is actually quite strong, so it doesn’t pose as much of an issue in a Toyota as it does in some other vehicles. However for this reason, a drop in style locker is not recommended for large tyres and big horsepower motors.
- Harsh re-engagement. Again newer designs are better than some of the older ones here, but drop in lockers do tend to be a little harsher than their full carrier counterparts when re-engaging. It is not uncommon to hear a loud click when the locker re-engages after cornering.
Full Carrier Locker
A full carrier locker completely replaces the factory center. As you can see in the picture above, the ring gear bolts directly to the locker itself.
- Strength. The locker carrier cases have been designed from the ground up to handle the loads needed for a locked differential. Most of the decent ones on the market are made from 8620 tool steel.
- Smoother operation.
- Price. Being a full carrier replacement, the units are quite large and heavy making them more expensive than a drop in locker.
From The Trenches
I’ve heard many a debate around the campfire and online about Automatic Lockers and Selectable Lockers, so I don’t intend to get into a pissing match over what is best. Do your own research, drive some different configurations and make up your own mind as to what suits you best according to your budget and needs.
However, I often hear people carrying on about how an automatic locker drastically changes the vehicles driving characteristics on road and that they are dangerous.
Here’s what they will do ; when the rear end it locked you will notice some understeer, which can then turn to oversteer once the locker disengages. Now unless you are driving like a complete idiot, you won’t really notice this much at all, definately not enough to lose control of the vehicle. You do need to make some slight modification to your driving style and you do notice they are there unlike a selectable locker which is only engaged when you need it.