Spicer 3-3-4391X Slip Yoke Assembly is a slip yoke, the sliding-spline half of a driveshaft that lets the shaft’s effective length change slightly as the vehicle’s suspension moves, while still carrying the U-joint at its end.
A universal joint (U-joint) connects two rotating shafts that aren’t perfectly in line, allowing power to transfer around an angle. It consists of a cross-shaped center piece (the “spider” or “cross”) with four trunnions, each fitted into a bearing cap held by a yoke on either shaft end. As the shafts rotate, the cross pivots within the yokes, letting the joint flex through the operating angle while still transmitting torque. U-joints are used in pairs on most driveshafts so the speed fluctuation each single joint introduces cancels out.
Match the U-joint series number (e.g., 1310, 1330, 1350) to your driveshaft — series numbers indicate the cap diameter and overall size, and they are not interchangeable across series. Check cap-to-cap width and cap diameter against your yoke, since two joints of the same series can still differ in these dimensions across vehicle applications. Confirm whether your application needs a greasable joint (has a zerk fitting for periodic lubrication) or a non-greasable, sealed-for-life joint. If replacing on a specific vehicle or PTO shaft, match against the OEM part number or confirm fitment against year/make/model rather than by size alone — the same physical joint size is used across many different applications.
U-joints and yokes are used on vehicle driveshafts (front and rear), farm and agricultural PTO shafts, industrial line shafts, and any drivetrain where the connected shafts operate at a working angle rather than perfectly aligned. Common replacement scenarios include driveline vibration, clunking on acceleration/deceleration, or visible wear/play in the joint.
To confirm fitment, measure cap-to-cap width and cap diameter directly against your existing part, or check the OEM part number stamped on it, or match against your vehicle/equipment year, make, and model rather than by size alone.
