rache

So in a nut shell, you are saying that there is no wind-up on a slippery surface like the one in the opening post video? I have had a VC on a bench, cut them open etc (see pic) and the reason why you can't turn them by hand (when working) is because the seals are so tight to cope with the high pressure that can occur within them I believe that the seals offer somewhere like 40Nm resistance (please don't quote me on that figure but I do have an SAE paper with the figure). You can undo the grub screw so that no pressure can build up or cut on in half, but either way, you will find that it is the seal that prevents it being turned. Some people 'test' a VC with a bar an watch how easily if falls/rotates but this is only a test of the seal which will loosen over prolonged use.

The rear differential is geared so that the rear half of the propeller shaft turns 8% faster than the front half to ensure that no drive goes to the rear wheels in normal road driving when the only the front wheels drive and the rear ones get dragged and rotate the rear propshaft/VC just slightly faster. The VC is not activated by this small speed difference, for if it was, it would try to slow the rear wheels, which wud be a braking effect on the car. Technical References: Landrover Workshop Manual (Description and Operation) 47.6, states: “The rear wheels are 0.8% under driven, so in most conditions the vehicle is effectively front wheel drive, with the rear wheels turning the rear propeller shaft slightly faster than the IRD drives the front propeller shaft. Since the speed differential is low, the increase in viscosity of the silicon jelly is marginal and there is little resistance to relative rotation of the slotted discs." However, the rolling diameter of worn tyres on the rear compared to new one on the front could adjust the 0.8%, hence the advice to fit new tyres to the rear in preference to the front. Wrong tyre pressures and conflicting rolling diameters can create a braking effect in the VC and have an impact on fuel consumption. One on front and one on rear would seem to be theoretically the best solution for VC issues but there may be a conflict with braking balance across axles although I imagine that ABS would counter such a problem? This is a shame, because since the front tyres do more braking than the rears, it would normally be a preference to have the best tyres where they are needed more.

Thanx for the replies, but from the quote in my opening post, you will see that the driver is saying that the wheel spin is caused by a perfect working VC. Perhaps if we take this one at a time, can you get wind up on the slippery surface as seen in the video in any vehicle? It is my belief that the wheel spin see (accompanied by exhaust and engine revs) is caused by the driver using the throttle and not the build up of wind-up? I accept that to make the rear wheels spin the front ones must be spinning although they are out of camera view and this shows the VC transferring drive to the rear wheels, but the question is; Is that wheel spin caused by transmission wind-up as claimed in the quote in my opening post? Its just that when I repeated the test, the wheels didn't spin as seen here and so wondered why the same car is not doing it immediately after the first video was taken? Also, if transmission wind-up is a constant thing caused by turning in a tight circle, why is the wheel spin only intermittent? I really think the first video is a hoax - am I right?

Hi, I was wondering just what is going on in the video below? The driver is saying this that the wheel spin that can be seen is caused by transmission wind up and not his use of the throttle as I believe. I accept that the Sportrak with a mechanical 4wd and no centre differential can suffer wind up if used on the road in 4wd, but didn't think it was possible on a slippery surface like in the video. But I don't think that Viscous coupling systems could have wind up in any circumstances. The driver has said this: "The tight turning circle I did was to try and show there is some wind-up occurring between the axles on the Sportrak (as would be expected because of no central differential), however even though there is a viscous differential on the Freelander there appears to be some seen on them, more so on the benchmark vehicle. I suspect there is less resistance between the tyre and the ground than the resistance in the viscous differential. The release of wind up can be seen as a momentary increase in speed of the left-hand rear wheel because it is taking the tightest radius." Is he trying to pull the wool over someone's eye? Here the video he is explaining: