* U-joints (Universal Joints): These are crucial for transmitting power from the transmission to the axles. Worn or damaged U-joints are a very common cause of vibrations that worsen under acceleration. The vibration often stops when the power is reduced.
* Drive shafts (Axle shafts): Similar to U-joints, worn bearings or internal damage within the axle shafts themselves can cause vibrations under load.
* Wheel bearings: Worn wheel bearings in the front can also create a vibration that increases with speed and load (acceleration).
* Balance Issues (Tires/Wheels): While less likely to only happen under acceleration, imbalanced tires or wheels could contribute. If the shake is *only* under acceleration, it's probably not the main problem, but it's worth checking.
* CV Joints (Constant Velocity Joints): These are found on the inner and outer ends of the front axles in many 4WD vehicles. Worn CV joints are another frequent cause of vibrations, especially under acceleration and turning.
* Transmission Problems (Less Likely): While less probable given the specific symptom, a transmission problem could *indirectly* cause this. A problem inside the transmission could transmit vibrations to the drivetrain under load. This is less likely because the shaking stops as soon as you let off the gas.
Troubleshooting Steps:
1. Check Tires and Wheels: Ensure tires are properly inflated and balanced. Look for any obvious damage to the wheels or tires.
2. Visual Inspection: Carefully inspect the driveshafts, U-joints, and CV joints for any visible damage like cracks, leaks (grease), or excessive play (movement).
3. Listen for Noises: Listen carefully for unusual noises (clicking, grinding, humming) coming from the front end, especially under acceleration.
4. Professional Inspection: Given the age of the vehicle and the potential for multiple components to be involved, taking it to a mechanic for a professional diagnosis is strongly recommended. They have the tools and expertise to properly diagnose the problem and ensure safe repair.
Ignoring the problem could lead to further damage and potentially dangerous driving conditions. Get it checked out promptly.
