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ECHANIC CONNECTION By Gary Goms, commercial accounts editor
Universal Joints Transmit Torque To An Axle n Europe and America, the com- many applications, a correct part at, let’s say, a 15-degree angle, the mon “universal” joint is often number can be obtained only by drive shaft will rotate smoothly unreferred to as a Cardan joint, in comparing the cap diameters and der most conditions of speed and honor of Gerolamo Cardano, cross lengths with charts supplied load. Last, the trunnions of each uwho invented the concept of using in your parts catalog. joint must be aligned along the a double-hinged joint to transsame plane on two-piece drive mit rotating torque in 1545. shafts. Inadvertently mis-alignDuring the the early 1800s, ing or installing one drive shaft Cardan joints became common out of phase or clock angle in many industrial with the other will usually reapplications and, when the sult in a vibration complaint automobile became popular under varying conditions of during the early 20th century, speed and load. Cardan joints were used for transmitting torque from the Installation Tips transmission to the rear axle. To prevent damaging the drive Today, Cardan or “universal” shaft, a universal joint press joints are a common replacetool should be used for replacment part in most rear-wheeling u-joints. The retaining clip drive automotive applications. Replacing u-joints with a universal joint press will grooves should be cleaned and help prevent damage to the new universal joint and lubricated before installation. In most applications, a single to the drive shaft. Note the orientation of the u-joint To prevent broken needle Cardan u-joint is attached to each end of a drive shaft. Dou- and drive shaft grease zerks. bearings, a viscous wheel ble Cardan joints are most bearing grease should be used commonly found on the front drive U-Joint Alignment to hold the needle bearings in shafts of four-wheel drive vehicles It’s important to understand that, place during assembly. The matbecause they can smoothly transas power is transmitted through a ing surfaces of the caps and the mit high torque loads at sharp single universal joint, the drive drive shaft loops should be lubriangles. shaft tends to accelerate and decelcated to ease installation. If so erate as it turns. Installing a second equipped, the grease zerks on U-Joint Terminology u-joint along the same plane as the each universal joint should point A typical u-joint uses a cross-shaft first u-joint will cancel this effect. toward the drive shaft and aligned or “cross” to connect one driven For that reason, many noise, vibraalong the same plane. After the shaft to another. The bearing portion and harshness (NVH) comuniversal joint is pressed in place, tion of modern universal joints is plaints on rear-wheel drive the drive shaft loops should be called a “trunnion” or “cap” convehicles are caused by incorrectly lightly tapped with a hammer to taining lubricated needle bearings. installed universal joints. To illusalign the caps with the cross. The A double Cardan joint also incortrate, the operating angles of each u-bolts fastening the u-joint to the porates a spring-loaded centering u-joint must be equal at each end drive axle flange should be inpin and ball assembly to keep both of the drive shaft. If the first joint spected for worn threads and rejoints rotating on a common center. operates at a 20-degree angle and placed if needed. Last, both joints Some u-joints, most commonly rethe second joint at a zero-degree should be lubricated with with a ferred to as “conversion” joints, are angle, the effect would the same as high-quality, water-resistant wheel built with unequal-length crosses using a single u-joint. On the other bearing grease after the drive shaft and unequal-diameters caps. In hand, if both joints are operating is installed. CM
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June 2013 | Counterman