Drive Shaft Universal Joint

What a U-joint does

A universal joint connects a driveshaft to the transmission, transfer case or axle while allowing the shaft to change angle as the suspension moves. A forged cross has four bearing caps that pivot, which lets torque pass through at an angle. They are wear items, and a worn joint can cause vibration, clunks on takeoff or a squeak.

Identifying the right joint

U-joints are sized by series and by measurements. The most important are cap diameter, overall width and the way the caps are retained.

• Series, such as Spicer 1310 or 1330, reflect size and torque capacity. A larger series carries more load.
• Cup size is the diameter of the bearing cap, like 1.062 inch in a listing.
• Outside-to-outside width is the distance across the caps, and it must match.
• Retention: outside snap rings sit outside the yoke, while inside snap rings and other designs fit different yokes.
• Greaseable or sealed: some have a grease fitting for maintenance.

Crossover joints

A crossover or conversion U-joint has two cup sizes so that a shaft from one series can connect to a yoke of another, as seen with a 1310 to 1350 listing. These are useful when mixing parts, but double-check both sizes before ordering. A driveshaft may need different joints at each end.

Strength and use

Larger tires, lockers, lift kits and extra torque increase stress on driveline parts. Many off-road builders choose a heavier series and a greaseable design, then maintain it often. Check the vehicle's specifications and compare joint series before upgrading. Remember that a stronger joint does not change the strength of the shaft or yoke.

Installation notes

• Mark the shaft position so balance is preserved when you reinstall.
• Press joints in with a vise or press tool, avoiding hammer blows on the caps.
• Seat snap rings fully and make sure the joint moves freely.
• Grease greaseable joints until fresh grease appears at the seals, and recheck intervals.
• Torque the driveshaft bolts to specification.

A bent or out-of-balance driveshaft can cause vibration even with new joints, so a driveline shop can help with diagnosis. Confirm fitment for your vehicle and axle before choosing.

Inspection, driveline angles and mistakes

To check a joint, shut off the engine, put the vehicle in park or in gear with the brake on, and try to twist and lift the driveshaft by hand. Any movement in the cap, a rusty brown stain at a seal or a stiff, notchy pivot means the joint is wearing out. Replace both joints on a shaft if one has failed from age, as the other is likely close behind.

• Do not hammer on the caps, which damages needle bearings.
• Do not reuse snap rings that are bent or loose in their grooves.
• Do not ignore a vibration, as a failing joint can break and let the shaft drop.
• Check slip yoke splines and grease them if the shaft has a fitting.

Lifted vehicles often have steeper joint angles. Joints work best when the angles at both ends of a shaft are close to equal and small. Large angles speed wear and may cause vibration, so some owners add a carrier bearing spacer, shims or a double-cardan shaft. Keep in mind that this category contains the joints only, so confirm yokes, flanges and shaft ends separately.