Drivetrain Issues:
* Driveshaft Problems: A worn or damaged U-joint in the driveshaft is a very common cause of shuddering, especially under load during acceleration and turning. The uneven forces on the driveshaft during a turn exacerbate the problem if a U-joint is failing.
* Differential Problems: Problems within the rear differential, such as worn gears, a failing differential bearing, or low differential fluid, can cause shuddering, particularly during acceleration and turning. The added stress of turning highlights any existing issues.
* Transmission Problems: While less likely to be the sole cause of shuddering *only* during turns and acceleration, a failing transmission (low fluid, worn clutches, etc.) could contribute. This is more likely to manifest as a general shuddering, not just in turns.
* Wheel Bearings: Worn wheel bearings can cause a vibration that becomes more noticeable under load (acceleration) and when turning, as the bearing is stressed.
Suspension and Steering Issues:
* Uneven Tire Wear: Significant uneven tire wear can cause vibrations that are amplified during acceleration and cornering. Check your tire tread depth and pattern carefully.
* Worn Suspension Components: Worn ball joints, control arm bushings, or tie rod ends can lead to vibrations and shuddering, particularly during cornering. The added stress of acceleration makes it worse.
* Brakes: While less likely, warped brake rotors can sometimes cause a shuddering sensation when braking *and* accelerating, especially in a turn.
Other Potential Causes:
* Low Tire Pressure: Uneven tire pressure can cause vibrations and uneven handling.
* Loose Parts: A loose component somewhere in the drivetrain or suspension can cause a shudder.
Troubleshooting Steps:
1. Check Tire Pressure and Tread: Make sure all tires are inflated to the correct pressure (check the sticker on your driver's side doorjamb) and have even tread wear.
2. Inspect Driveshaft and U-joints: Look for any signs of damage or excessive play in the driveshaft U-joints. This often requires lifting the vehicle.
3. Check Differential Fluid: Check the rear differential fluid level and condition. Low or dirty fluid is a common problem.
4. Have a Mechanic Inspect Suspension Components: A professional mechanic can inspect your suspension components for wear and tear.
5. Brake Inspection: Have a mechanic inspect your brake rotors for warping.
Recommendation:
It's difficult to diagnose this problem remotely. The best course of action is to take your Ford Expedition to a qualified mechanic for a thorough inspection. They can pinpoint the exact cause and provide the necessary repairs. Describing the shuddering (when it occurs most intensely, at what speed, etc.) will help the mechanic diagnose the problem more accurately.
