* Driveshaft imbalance: A driveshaft that's bent, worn, or out of balance can cause vibrations at specific speeds. This is a common cause of speed-specific shimmies. It's often felt more strongly in the rear of the vehicle.
* Wheel bearing issue (even if seemingly tight): While you mentioned the front end is tight, a wheel bearing could be slightly damaged internally, leading to uneven rotation and vibration only apparent at certain speeds. A thorough inspection beyond just a "tightness" check is needed.
* Tire balancing (despite even wear): Even with even wear, tires might not be perfectly balanced. A slight imbalance can amplify at higher speeds, causing a shimmy. Consider having them re-balanced, including a road force balance if available. This is crucial, even if they appear fine.
* Steering linkage: A worn tie rod end, ball joint, or other steering component could be causing play that manifests as a shimmy at a specific speed. Even small amounts of play can cause this. Look for any play in the steering linkage during a thorough inspection.
* Differential issues: Problems within the differential (bearings, gears) could cause vibrations that transmit to the chassis.
* Bent rim: A slightly bent wheel rim, even if not visually obvious, can cause vibrations. Inspect the wheels carefully for any imperfections.
Troubleshooting Steps:
1. Road force balance the tires: This is the most likely culprit if everything else is fine.
2. Carefully inspect the driveshaft: Look for bends, damage, or play in the u-joints.
3. Thoroughly inspect all steering components: Look for any play in the tie rod ends, ball joints, etc. This often requires jacking up the vehicle and checking manually.
4. Check wheel bearings again: Look for play or roughness in the wheel bearings, not just tightness.
5. Have a professional inspect the differential: This requires specialized tools and knowledge.
Ignoring the shimmy can lead to further damage, so getting it properly diagnosed is important. Starting with a road force balance is a good first step, as it's relatively inexpensive and often resolves this issue. If that doesn't fix it, a professional mechanic specializing in older Jeeps would be your best bet.
