How to Troubleshoot a U-Joint

Universal joints compensate for the offset between the transmission and the rear differential, as well as the variable height of the differential as the suspension allows the rear axle to move up and down. The U-joint consists of a yoke on each end of the drive shaft that connects to the yokes on the transmission and the rear differential via the U-joint bearing. Bearing wear because of lack of lubrication or hard use can introduce play into the U-joint and ultimately lead to failure. Bad U-joints display symptoms that can be confused with other drivetrain problems, but can easily be isolated as the problem with a few tests.

Things You'll Need

• Wheel chocks
• Jack
• 2 jack stands
• Wrench set

Instructions

1. Start the engine. Press firmly on the brake pedal and put the transmission in “Drive.” Listen for a clicking or clunking sound as the transmission engages. Shift to “Reverse” and listen again. The noise may indicate a bad U-joint bearing. To test in manual transmission vehicles, set the emergency brake and let the clutch out enough to turn the drive shaft slightly without stalling the engine.

2. Turn the engine off. Chock the front wheels. Raise the rear of the vehicle using a jack at the approved jacking points. Support the vehicle on jack stands.

3. Inspect all of the U-joints for signs of lubrication containment failure. Bad U-joints will have a greasy or caked appearance from road grime trapped by the bearing grease. This indicates the seals are gone on the bearings and that they will fail soon. Replace the bearings.

4. Inspect the bearing caps on each side of the yoke and make certain they are tight. Tighten any loose bearing caps with a wrench before proceeding.

5. Grab the drive shaft near each U-joint and alternately push and pull on the shaft. There should be no relative motion between the shaft yoke and its mate. Any relative motion or noise while performing this step indicates worn bearings that need replacing.

6. Inspect the boot on constant velocity type U-joints for tears or signs of escaping grease. Replace according to manufacturer’s procedures.

Tips & Warnings

• Many vehicles have multiple drive shaft sections, supported by a center bearing, to complete the drivetrain. Inspect the center bearing for play and replace it as necessary.

• Consult the vehicle manufacturer’s service procedures for model specific information on replacing and lubricating the U-joint bearings.