The Quest for All-The-Time All-Wheel-Drive

Sir,

In the article “Rover Recap” in your January issue you made the following statement about Rover’s first turbine car: “The T3 is interesting because it successfully used 4-w-d with a differential at each end and a free-wheel between them before Ferguson emphasised the possibilities of all-wheel-drive.” With all respect, that statement was inaccurate in two respects: first, the 4-w-d arrangement in the T3 was not successful, and secondly, the experiment did not precede Ferguson’s emphasis on the possibilities of all-wheel-drive.

The T3 4-w-d -system, using a free-wheel between the front and rear differentials, was unsuccessful and abandoned in the T4 in favour of f-w-d for the reason for which Ferguson threw over that and other similar systems in their quest for genuine all-wheel-drive at all times and in all conditions, without penalties. The free-wheel device between front and rear diffs, not only failed to cope with “circumferential” tyre-scrub caused by overloading on the rear wheels or deflation or heavy wear of the rear tyres, but had the serious drawback of giving the vehicle sometimes four-wheel-drive and “coupled” braking and sometimes not, depending on the amount of steering-lock applied. Consequently, the driver, particularly of course, when cornering, could never be certain whether the drive was getting through to all wheels or only two. This was, clearly, disconcerting and dangerous, and put out of court yet another attempted solution of the problem of achieving a method of driving all wheels on or off the road and at any speed without cornering or circumferential tyre-scrub, wind-up and excessive fuel consumption.

The search for such a system had been going on for a long time before Rover and, indeed, before Freddie Dixon and Tony Rolt, a good deal earlier than Rover, joined in it. It dates back, in fact, to 1907 when Otto Zachow, of Cliftonville, Wisconsin – asking “whoever is it who ever heard of a mule walking only on two legs ?” – designed and built the first 4-w-d car after having solved the problem of steering the driven front wheels by the invention of a device consisting of a double-Y universal joint and a ball and socket.

This was the forerunner of a long line of all-wheel-drive vehicles, represented today by the Jeep, the Land-Rover, the Gipsy and a good many more, which are effective for off-the-highway use and on snowbound or muddy roads but are subject to all the penalties mentioned above when driven on hard surfaces because the drive system is “solid.” They have, therefore, to be taken out of all-wheel-drive when driven on the road at any speed.

To overcome this drawback many experiments were made. They included a conventional centre differential, which is still used in some vehicles, but has the decisive disadvantage that, if one wheel loses traction, so do all the rest. Free-wheels, as in the T3 and a number of American racing cars in the ‘thirties, were tried and abandoned for the reasons already given. At an early stage Ferguson played with four-wheel steering (“the Crab”) but this was too complicated and fundamentally wrong at anything but very low speeds. Ferguson also tried front-wheel swing axle steering but this had inherent faults and involved unacceptable encroachment of the front wheel arches into the body-space if a reasonable turning-circle was to be obtained. Even central steering, with the passengers grouped round the driver, was envisaged to mitigate this last disadvantage but was dropped as unacceptable from a sales point of view.

The late Mr. Harry Ferguson, determined to have all-the-time all-wheel-drive and equalised braking all-round for safety reasons, was not, however, to be beaten. He wanted between the front and rear differentials “a diff, which will diff when it ought to and won’t diff, when it shouldn’t.” Tony Rob, Claude Hill and their team eventually gave him what he wanted. It was the break-through. The quest was over.

N. F. Newsome, Director,

Harry Ferguson Research, Ltd.

Coventry.