The Discovery has ARB Air Lockers on the front and rear axles, which was a major selling point for purchasing it. Over the last two years of ownership, they have had mixed results overall.
Here a few reasons I am not fully sold on Air Lockers:
Too many moving parts in the system.
In order for Air Lockers to work, it requires not only the lockers but also an air source, hoses and air solenoids to get the whole system to work.
In our case, when the Discovery was purchased, it only had the locking differential, but one of the other hardware was included. We were able to put together all the parts to get this working, but it was expensive.
ARB Air Locker with Perished O-rings
Maintenance is a pain.
There are two O-rings that seal around the shaft of the of the axel to control the flow of air into the locking mechanisms. These have to be replaced periodically, and it’s a massive pain because it requires removing the whole differential from the housing. In the two times, we have had to do this, it’s taken 3 to 5 hours to complete the job. You end up laying on your side trying to get the diff into place, which I think is at least 80 pounds, all while trying not to bump the fragile copper line that supplies the air to the locking mechanism. It is quite a challenge.
You have to stop to activate them.
This is one is on the driving side when you’re on the trail and you need to lock the diffs, it requires coming to a full stop. This requires careful consideration of each obstacle, as when the system is locked, it’s very hard to turn, so you really have to pick and choose when you turn them on. If you’re trying to bump over an obstacle and things start spinning, you have to come to a full stop, engage the lockers and start over.
In our experience it seems like for most off-road driving, auto lockers provide simpler experience, as they lock when traction is lost, and then unlock as it’s regained, with no user interaction on stopping required. While the finite control is lost with Auto Lockers, it seems like it’s vastly made up for in ease of use and lower maintenance requirements.
All that having been said, the ARB Air Lockers, when they are working, work very well, and have certainly made the difference in getting over quite a few obstacles that would have required winching otherwise.