Here is my take about when and how to engage differential locks.

by the way, a differential lock and a locking diffeential are not the same thing

Locking your diff - more...

On dry pavement - Never! You’ll lose all ability to steer. Bad!

On pavement with snow and ice engage your locker(s) whenever you think there is a need to keep the tires from spinning as long as you are driving straight. Disengage the front way before you would get into a turn, or severe understeer would occur.

Lockers can be engaged while the vehicle is moving - at any speed. But like in difficult off-road stuff you should be moving rather slowly on snow and ice. Especially when the surface is uneven, loss of traction is likely. In snow an inch of downtravel of one tire could result in a spinning tire. So, as a good driver you should engage the locker(s) proactively before wheelspin occurs.
Remember, lockers were designed to prevent wheelspin. All the new electronic stuff is reactive. Wheelspin has to happen first and then the system tries to rescue what’s lost. Manual lockers are 100 times better.

Proper use of lockers off-road provides enough material for a small book - in fact I am working on one. As a good driver you should engage the locker(s) proactively before wheelspin occurs. Especially when the surface is uneven (and isn't that part of the off-road definition?) loss of traction is likely. Depending on your spring set up (long and soft or short and hard) downtravel of only one tire could result in two spinning tires - the diagonally opposed tire of the one that encounters downtravel will also move out of the fenderwell and could lose traction as well.

Even the best driver sometimes goofs. Forgets to lock the diff(s). No worries! As long as the spinning tire(s) are not much faster than the slower tire(s) or your rpm are around 1000 with a manual and below 1500 with an automatic you can still safely lock the diff(s).

The diff locks should not be engaged once you leave pavement just to have them on, in case someting could happen during the next hour or so. Lockers need to be used briefly and strategically when needed. A moment here and there should be enough. I sometimes use them only for a second or so - just enough to maintain or regain traction. I switch them off so quickly because I want to maintain maximum steering capability at all times.

Special attention needs to be put on whether to use the front or the rear locker - or both. The inside scoop will be in my book.

If you want to learn all the ins and outs of using lockers (including the incredible tricks you can perform with your front locker), use of low range, proper tire pressure etc. etc. you may want to sign up for one of my 4x4 seminars - otherwise you'll have to wait for my book on lockers.

The Mercedes axle diff lock is a dog cluch setup with 5 big strong teeth (see below). As long as the difference in speed between both axles sides is not too much, the teeth of the locker will find their way safely into the groves.
At 1000 rpm in first gear low range each tire rotates at 25rpm - so, even if one tire starts rotating faster, it will only be10 or 20 rpm more. Not much. The diff lock mechanism can take that.
However, if you panic when losing traction and step on the gas more (it is most people’s gut reaction) and then engage the diff lock(s) you might do some internal damage.


When and why to lock your differential locker - more..

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