thanks for shedding more light onto the subject , and do we have only two combination arrangments .ie. rear alone or rear and front diff locks in addition to central one?
@ Laparwah, its a rather long to explain completely in writing, I am copying/pasting below one of my previous replies in another post (the link of which is mentioned in my initial reply). Nomi's youtube link is a very simplified yet detailed explanation, but it doesn't entirely explain what happens in any ordinary 4X4. Anyway here goes my previous explanation;
[highlight][highlight]Diff locks in 4X4s are: Central, to make sure equal torque distribution to front and rear wheels. Additonally in some vehicles there are separate front and rear diff locks to make sure that equal torque is sent to right and left wheels. Theoratically one would have the most traction with all diff locks engaged, however lots of other things come into play (to avoid wheel spinning/ improving traction) including the tyres and suspension (tyre contact/grip to any surface depends on your suspension, be it off-road or onroad vehicle).
Limitations of full diff locks is that it can be used on only slippery surfaces as wheel speed on all 4 tyres is same. Which mean that transmission is under lots of stress when turning etc because wheels are covering different distances in turns (ouside more that inside tyres). You can actually snap your transmission on grippy surface by constantly turning with full diff locks engaged.
Diff locks are meant to help in avoiding the wheel spins, so you can keep moving forwards (or backwards). Theoretically in most 4X4s, when on steep uphill slope with two wheels on ice/very slippery surface, the vehicle would not move forward, but rather the wheels on slippery surface would keep spinning. So in real term these vehicles are not 4 wheel drive. However if you have full locks on than this could be avoided, as tyres on left and right side can only turn at one speed, so no power is wasted on spinning.
Manufacturers use various other things to avoid wheel spin as well, like Limited slip differential, torsen diff locks, traction control systems etc.
Most Proper 4X4s would have central diff lock. Vehicles with part time 4X4 would by default have centrally locked diff anyway (90% of older 4X4s you come across are only part tiem 4X4, i.e they oldly engage front shaft on demand and not all the time. Soft roaders mostly wouldn't have centre diff lock. Very few 4X4s would offer full diff locks even as an option. G-Wagens have offered them standard from beginning (apart for G500 for some model years), Some models of Jeeps and I beleive Hummer H1 also had them.
As far as I know Defenders and even other land rovers/ range rovers would mostly just have central diff locks. Rear diff locks were I think offered in some defender models recently. Range Rovers and discovery's would have some kind of electronic traction / tyre slip control mechanism installed. But they mostly can make up for that from there excellent suspension.
Landcruisers series 60, 70 and 80 had front and rear diff locks only as an option. In Series 100 only rear diff locks were available, but 105 had solid front axle so it had full diff lock option. Not sure about series 200. I think its similar for old and new Prados. [/highlight][/highlight]
Maybe we can discuss it further when ever we meet up in any of the IJC offroad events.