A common problem in "Jimnyworld" is to travel to an off-road event only to find that you cannot select 4WD. Either the hubs are stuck or the vacuum has "escaped". For more details on the hubs see my "How to guide"
You usually only find this out when you get stuck in the simplest of mud puddles whilst an appreciative crowd looks on and crys out "Put it in 4WD, mate!"
Normally this signals the end of your day out before it has even begun, but not if you invest in one of these tools.....
...an E10 Torx socket (see www.halfords.com for an example price). You should carry one of these AT ALL TIMES anyway as you will need it to cover you for any drive shaft issues.
Put the car in 4WD. Remove the 6 bolts around the hub using the above tool. The picture below shows an UNLOCKED hub
Reach inside the inner ring with a finger. Wiggle the inner ring from side-to-side and gently pull it forward with you finger.
It will suddenly spring forward into the LOCKED position (see picture below.
Now simply gently replace the hub (making sure you engage the splines without pushing to hard on it) and bolt it up. If necessary repeat for the other side.
Reversal is simply the opposite procedure. Put the car in 2WD. Remove the hub. If it is still locked then gently push the inner ring down, it will resist against the spring but then click down into the unlocked position.
I did this last Sunday and in less that 5 minutes saved a days off-roading.