Driveline wind up

The Ferret was a popular and efficient vehicle in Army service. Its only weakness is generally considered to be the potential for wind-up, due to the fact that it is a permanent four-wheel drive. The Ferret has a single H-differential and thus a virtually a solid connection between its front and back wheels on each side. Wind-up will happen on hard surfaces and sealed roads. Hitting the wheels on the dirt or gravel roadside occasionally only relieves wind-up between nearside front and rear, unless you can get all four wheels off the road.

When a car corners, all four wheels rotate at different speeds since each follows a different imaginary circle. The two wheels on the inside of the turn rotate slower than the pair on the outside, for they follow a smaller radius circle. The front wheels must rotate faster than the rear ones, for they follow a larger radius circle. For best traction both front and rear wheels ideally should propel the vehicle. Therefore a differential or transaxle (a combined transmission and differential) is required, to allow differing rotational speeds. Without a differential either the inner wheel rotates too fast or the outer wheel drags, which results in difficult and unpredictable handling, damage to tyres and strain on, or possible failure of, the entire drivetrain.

Try and catch potholes, manhole covers and catseyes to give the wheels bumpiness, allowing them to unwind.  Constant ‘circular’ driving – even if it is not tight circles (e.g. constant left-hand/right-hand turns) will result in wind up. Vary the route all the time. Take the opportunity to go over uneven ground, bumps, potholes, manhole covers and sleeping policemen.

I’ve spray-painted hour clock hands on my wheel hubs easily to keep a useful check on transmission wind-up. This practice was never official, but sometimes you’ll see photos of a Ferret in service with a line painted across the diameter of the wheel hub. If the wheels on each side  gets really bad and the lines are not parallel, I’ll jack up the wheels on each side to relieve wind-up tension (ensure the other side is chocked!).

Whilst in service wind-up was not generally a problem. Checks for slackness were carried out every 500 miles and the local REME workshop could quickly repair any loose wheels. With fewer parts now available, it is more of a challenge for civilian owners. The dowels and bolts that work loose with wind-up can be seen in part (4) of this picture of the epicyclic reduction gears. This page explains how the transmission of the Ferret is constructed, and how wind-up occurs. You’ll also find an illustrated protocol showing the repair of a wheel station.