Juddian:
I can’t get me head round what speed the wheels still turning (the pair opposite the locked wheel) would be doing, would it be road speed (same as the other pair still driving normally) or would they be turning faster than actual speed.Forgive me if its a daft question.
Not a daft question at all. In fact, on a single driving axle arrangement, ie 6x2/4x2 or whatever, the wheel which is free to turn will in fact rotate at twice the normal speed. Why? I don’t know, but it does. I have asked qualified motor/mechanical engineers about the phenomenon, and no one has been able accurately to tell me.
However, in the case described by newmercman, the vehicle was a 6x4, and I think, but I may be proved wrong, that the third diff (interaxle) would permit differentiation between the front and rear axles, (which is why it is there) and the vehicle would proceed normally, except of course that one set of wheels on one or other axle is not turning.
If it makes it any easier to understand, you can fit a double drive bogie with two completely different final drive ratios, and as long as you never engage the interaxle lock, the vehicle will drive normally, at a speed determined by the lower of the two diff ratios.
Engage the interaxle lock, however, particularly when moving and you will instantly have a very expensive pile of scrap.
Tonight’s gold star goes to JUDDIAN! !!