A rag joint refers to certain flexible

joints A joint or articulation (or articular surface) is the connection made between bones, ossicles, or other hard structures in the body which link an animal's skeletal system into a functional whole.Saladin, Ken. Anatomy & Physiology. 7th ed. McGraw- ...

( flexure bearings) found on

automobile A car, or an automobile, is a motor vehicle with wheels. Most definitions of cars state that they run primarily on roads, Car seat, seat one to eight people, have four wheels, and mainly transport private transport#Personal transport, peopl ...

s and other machines. They are typically found on steering column shafts that connect the

steering wheel A steering wheel (also called a driving wheel, a hand wheel, or simply wheel) is a type of steering control in vehicles. Steering wheels are used in most modern land vehicles, including all mass-production automobiles, buses, light and hea ...

to the

steering Steering is the control of the direction of motion or the components that enable its control. Steering is achieved through various arrangements, among them ailerons for airplanes, rudders for boats, cylic tilting of rotors for helicopters, ...

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 Vibration () is a mechanical phenomenon whereby oscillations occur about an equilibrium point. Vibration may be deterministic if the oscillations can be characterised precisely (e.g. the periodic motion of a pendulum), or random if the os ...

coming from the steering system, providing some isolation for the steering wheel. This type of joint has also been used on

drive shaft A drive shaft, driveshaft, driving shaft, tailshaft (Australian English), propeller shaft (prop shaft), or Cardan shaft (after Girolamo Cardano) is a component for transmitting mechanical power (physics), power, torque, and rotation, usually ...

s. Farm tractors and lawn and garden equipment have often used them in this application, and even some higher-power applications, such as some 1960s race cars, featured them. In automobile and truck prop shaft designs, they have now mostly been replaced by

constant-velocity joint A constant-velocity joint (also called a CV joint and homokinetic joint) is a mechanical coupling which allows the shafts to rotate freely (without an appreciable increase in friction or Backlash (engineering), backlash) and compensates for the a ...

s or driveshafts with pairs of

universal joint A universal joint (also called a universal coupling or U-joint) is a joint or coupling connecting rigid shafts whose axes are inclined to each other. It is commonly used in shafts that transmit rotary motion. It consists of a pair of hinges ...

s or '' giubos''. 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), or vice versa. This gives articulation where needed, but also stops some of the vibration being transmitted into the body. The joint consists of one or more

doughnut A doughnut or donut () is a type of pastry made from leavened fried dough. It is popular in many countries and is prepared in various forms as a sweet snack that can be homemade or purchased in bakeries, supermarkets, food stalls, and fran ...

-shaped layers of flat

rubber Rubber, also called India rubber, latex, Amazonian rubber, ''caucho'', or ''caoutchouc'', as initially produced, consists of polymers of the organic compound isoprene, with minor impurities of other organic compounds. Types of polyisoprene ...

sheet with reinforcing cords vulcanized in them, similar to a

tire A tire (North American English) or tyre (Commonwealth English) is a ring-shaped component that surrounds a Rim (wheel), wheel's rim to transfer a vehicle's load from the axle through the wheel to the ground and to provide Traction (engineeri ...

. In fact, they are cut from used tires. This disc is bolted or

rivet A rivet is a permanent mechanical fastener. Before being installed, a rivet consists of a smooth cylinder (geometry), cylindrical shaft with a head on one end. The end opposite the head is called the ''tail''. On installation, the deformed e ...

ed 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. The origins of this form of universal joint are from early vehicles that used a disk of thick

leather Leather is a strong, flexible and durable material obtained from the tanning (leather), tanning, or chemical treatment, of animal skins and hides to prevent decay. The most common leathers come from cattle, sheep, goats, equine animals, buffal ...

as a similar flexible joint. These were used into the 1920s. As rubber technology improved (particularly for its resistance to spilled mineral oils), it was possible to replace leather by longer-lasting materials. "Rag joints" were used on some American cars, including GM full size sedans, into the mid 90s. An older vehicle with loose steering or "play in the steering wheel" is often found to have a worn rag joint. One can reach inside the cab and wiggle the steering wheel while watching the rag joint move without the input shaft moving. This condition may cause the vehicle to fail the

vehicle inspection Vehicle inspection is a Standard Inspection Procedure, procedure mandated by national or subnational governments in many countries, in which a vehicle is inspected to ensure that it conforms to regulations governing Car safety, safety, Automobi ...

, indicating that the worn part needs replacement.

References

{{DEFAULTSORT:Rag Joint Rotating shaft couplings Automotive transmission technologies