The simple emergency brake for a tractor working on a slope has a brake arm hinged (4) under the chassis. The brake arm has a hooked end (1) which is driven into the ground by a servo brake cylinder (2). The servo force can be derived from pneumatic or hydraulic supplies and the brake is operated by an emergency control in the cab. One or more brake hooks are fitted and are positioned in such a way that their deployment does not inhibit the steering of the vehicle. A controlled braking effect can be obtained by regulating the degree of deployment of the hooks by controlling the servo brake pressure.
