The semi-elliptical back springs have central anchorages which can swivel about the axle case.
The First World War brought about large scale growth, providing axles for military vehicles and by 1930 most lorries and buses made in the UK had a Kirkstall back axle casing.
The rear wheels were driven through a Hotchkiss drive system modified with control arms linking the rear axle casing to pivot points on the frame located directly above the true pivot of the leaf springs.
Drive was taken to the rear wheels through a three-speed gearbox, light but very similar to the earlier car, and jointed drive shaft . The brake drum at the back of the gearbox surrounds the universal joint, the rear axle casing extends forward to almost the universal joint.