A rag joint refers to certain flexible joints (flexure bearings) found on automobiles. They are typically found on steering shafts that connect the steering wheel to the steering gear input shaft, usually at the steering gear end. They provide a small amount of flex for a steering shaft within a few degrees of the same plane as the steering gear input shaft. It also provides some damping of vibration coming from the steering system, providing some isolation for the steering wheel.
This type of joint was also used on drive shafts of 1960s race cars, later being replaced by the constant-velocity joint or driveshafts with pairs of universal joint. Rear-wheel drive cars have commonly used a lengthwise propeller shaft with a rubber doughnut joint at the gearbox end (limited movement) and a universal joint at the rear axle (greater movement). This gives articulation where needed, but also stops some of the vibration being transmitted into the body.
The joint consists of a piece of doughnut shaped rubber with reinforcing cords vulcanized in it, similar to a tire. This disc is bolted or riveted to flanges mounted on the ends of the shafts to connect the steering wheel shaft to the steering gear. The ragged cords can be seen on the edge of this piece of rubber, hence the term "rag joint". The bolt holes themselves are often reinforced by steel tubes moulded into the doughnut.
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