* Worn U-joints: This is the most obvious. U-joints are wear items and eventually fail. The constant flexing and stress eventually fatigue the metal, leading to cracking or breakage. Regular inspection and replacement at recommended intervals (or sooner if you notice issues) is key.
* Incorrect Installation: If a U-joint was improperly installed (incorrectly seated, damaged during installation, etc.), it won't last long. This is especially true if the caps weren't properly lubricated.
* Loose or Damaged Driveshaft: A bent, damaged, or misaligned driveshaft puts extra stress on the U-joints, causing premature failure. Inspect the driveshaft for bends, rust, or other damage. Check for play or looseness in the driveshaft components.
* Worn or Damaged Slip Yoke: If your Jeep has a slip yoke style driveshaft, a worn or damaged slip yoke can lead to excessive stress on the U-joints. A damaged boot will allow grease to leak out, further exacerbating the problem.
* Wheel Bearings: Bad wheel bearings can cause binding in the axles, putting extra strain on the U-joints. Listen for grinding or humming noises when driving, especially when turning.
* Misalignment: Any misalignment in the drivetrain, such as a pinion angle issue (the angle between the driveshaft and the differential), will place uneven stress on the U-joints leading to premature failure.
* Improper Lubrication: Lack of lubrication within the U-joints is a major cause of premature failure.
* Excessive Vibration: Excessive vibration from other sources in the drivetrain can fatigue U-joints.
To diagnose the problem:
1. Visual Inspection: Carefully examine the U-joints, driveshaft, and surrounding components for any signs of damage, wear, or misalignment. Look for cracks, excessive play, rust, or damage to the boots.
2. Check for Play: Grab the driveshaft at the U-joints and try to move it. Excessive play indicates a worn U-joint or other problem.
3. Inspect the Slip Yoke (if applicable): Check for excessive wear, damage, or leaks.
4. Check Wheel Bearings: Listen for noise and check for play in the wheels.
5. Professional Inspection: If you're not comfortable performing these checks yourself, take it to a mechanic specializing in Jeeps.
Replacing a U-joint isn't incredibly difficult, but if you're not mechanically inclined, it's best to have a professional handle it. Ignoring the problem will likely lead to more serious and costly repairs. Addressing the *cause* of the U-joint failures is crucial to prevent this from happening repeatedly.
