This construction was the first to appear in a larger series. With this type of drive-train, the otherwise non-driven axle is not brought in when necessary, but is permanently engaged. The most elegant realisation of an all-wheel drive, is probably only possible with a straight mounted engine and front-wheel drive. Apart from the gearbox alterations with the gearbox casing almost unchanged, the drive train 'only' needs to be complemented by a centre differential, a drive shaft and a driven rear axle. The latter two components are basically parts also found in the serial production. With front-wheel drive, the amount of effort required by the manufacturer for the conversion is lower than with a standard drive train (rear-wheel drive).

The (lower) gearbox output shaft is substantially altered. It becomes a hollow shaft and delivers it's torque to the rear to the casing of the central differential. Only a second shaft, inside the hollow shaft, delivers the power-flow from the (left) bevel wheel of the centre differential to the front axle. The torque from the rear (right) bevel wheel is transferred to the rear axle. This simple method of transferring to the front is only used with manual gearboxes and only in older drive-trains of this type. with automatic transmissions and newer Quattro-drive-trains there is - as with all-wheel-drive in standard drive-trains, once again, a shaft that goes past the gearbox to the front.

Here the first gear is selected. The torque is provided, as in a front-wheel drive, from wheel 1 to wheel 2, however, through the hollow shaft to the rear. There, the torque is transferred to the two bevel-wheels, 4 and 5, which only turn if the front axle has a different rotation speed than the rear axle does. Thus it carries on through the drive shaft to the rear and through the hollow shaft to the front.

It must be noted, that although four wheels are being driven here, no limited slip exists. That means, that if one wheel has no traction, despite having all-wheel drive, the car won't be able to go on.

Kamm's circle of forces, shows that a wheel can only build up either maximum advancement force (1) or maximum lateral force (2). Here you can see a wheel that transfers more propulsive force and only has a little left over for the lateral guidance.

Here is a wheel that is completely occupied with holding the car in a curve. It can only transfer little propulsive force. The advantage of permanent all-wheel drive, also on surfaces with a good amount of grip, is that the propulsive force is transferred by two axles, that means that more lateral guidance is provided by each axle than if the total torque must be put on the road by only one axle.

Here a vehicle is shown, where the front wheels are reaching the limits of the lateral guidance much more than the rear wheels are. Should this be the case, through the slight shifting of part of the torque to the rear axle, the lateral guidance is increased. 05/15