Aye Up Bumble,
With regard to your query re how does a part time 4x4 system work, a relative of mine was involved in the design of the systems employed on the Volvo XC, early Freelander, Renault RX4 etc and explained it to me like this - The engine drives the front wheels as per a normal FWD vehicle.
A further (forward) drive shaft runs towards the rear of the vehicle to a coupling approximately in the centre of the vehicle. Within the coupling is a material that is fluid when the forward drive shaft is rotating at a low speed, i.e. when the front wheels have grip. After the coupling the (rearward) shaft continues to the rear differential unit.
If a front wheel loses grip and spins the forward drive shaft faster than usual, the centre coupling fluid heats up, becomes almost sold and turns the rearward drive shaft and via the rear differential drives the rear wheels. I suspect that the Panda 4x4's use a similar system.
This probably explains why some of the Panda 4x4 vids on You Tube show a Panda with wheels spinning at the first attempts to negotiate an obstacle which they subsequently accomplish with ease. Once the fluid has warmed up the system probably kicks in almost instantaneously. Conversley when the fluid cools down the system reverts to back FWD. The Cross also has electronic diff locks fitted which I believe operate via the ABS system, locking out a spinning wheel but across the axles. Bear? in mind though that until the centre coupling has aleady been activated, drive will not be delivered to the rear wheels and so it is likely that the diff locks (and therefore traction) will only be supplied by the front wheels.
I tend to leave the diff locks off until I have experienced a bit of wheel spin and know that the rear wheels are driving as well as the front. After that the little marvel climbs or negotiates most surfaces with relative ease. So far the only limitations I have found with it are ground clearance and tyres but this has been in more extreme circumstances way beyond normal snow & ice conditions or even light forestry use.
As for the comment by fsmr re the Toureg - I previously owned a Freelander2 with all the bells and whistles (megabux) and it struggled where the Fiat prevailed!
Really informative - well done. I think the XC70 D5 is an amazing car. The part time four wheel drive has been incredible in the snow and, under normal use my automatic/geartronic gets me over 40mpg on average. One problem that has beset me a couple of times was when driving through very deep loose snow. The car lost power and a message "Urgent service required" was displayed on the dash. The car stayed in first gear and the engine, although not misfiring, wouldnt rev. I thought that it had defaulted to some sort of emergency 'get you home' mode and I drove it, very slowly to my local garage. My mechanic friend laughed, turned off the traction control and the car was immediately restored to full power. Apparently, this is common on such 4WD cars and is caused when ice/snow builds up on the ABS sensors on the front wheels. After a short drive, I turned the TC back on and all was well. Anyway, thanks for your explanation.
Steve
