In the case of the adjustable upper link in a three-point suspension device for a tractor, comprising a locking device in the form of a line fitted with a shut-off device and connecting together the two end-faces of the hydraulic cylinder, the invention simplifies the operation of the device in that it may be adjusted effortlessly from the tractor-seat. This is achieved in that the shut-off device is in the form of a ball-valve having an axis secured to a forked actuating lever, and in that springs are provided to urge the said actuating lever towards the shut-off position. A scale provides the tractor-driver with an accurate indication of the setting of the link. The design of a tube accommodating one end of the piston-rod as a compressed-air chamber ensures automatic displacement of the piston in the hydraulic cylinder.