* Driveshaft issues: A slightly bent driveshaft, worn U-joints (universal joints), or a problem with the center support bearing could cause a vibration in that specific speed range. These are tricky because they might not show up on a visual inspection or standard vibration analysis. The vibration is often felt more in the floorboard than the steering wheel.
* Tire balance or condition: Even with low mileage, tires can become unbalanced over time or develop subtle imperfections. Have a *thorough* tire rotation and balancing done, including checking for any unusual wear patterns that might indicate a suspension problem. Consider new tires if the current ones are showing significant wear or age.
* Wheel bearing: A slightly worn wheel bearing can create a vibration that’s speed-dependent. It often presents as a hum or growl but can manifest as a shake, especially at certain speeds.
* Brake rotor warp: While less common with relatively low mileage, warped brake rotors can cause a vibration, particularly at lower speeds. However, this usually presents as a pulsing in the brake pedal, so this is less likely.
* Suspension components: Worn control arm bushings, ball joints, or tie rod ends can contribute to vibrations, though typically a more general vibration rather than limited to 35-45 mph.
* Transmission mount(s): A worn transmission mount can allow excessive movement of the transmission, leading to vibrations.
What to do next:
1. Second opinion: Get a second opinion from a different mechanic, specifically mentioning the speed range of the vibration. Explain that the first mechanic found nothing. Emphasize the 35-45 mph range – it's key information.
2. Road test with a mechanic: If possible, take the car for a test drive with the mechanic. This allows them to experience the vibration firsthand and possibly notice subtle clues.
3. Focus on the driveshaft: Since many of the other possibilities have been ruled out, focus the second opinion specifically on the driveshaft, U-joints, and center support bearing. These are relatively common culprits for speed-specific vibrations.
4. Tire balancing and rotation (again): Even if it was done recently, this is crucial. Sometimes a slight imbalance only shows up under certain conditions.
The fact that the problem is speed-specific makes it more challenging. It's not a general vibration indicating a major issue, which makes diagnosis tricky. Persistence and a second opinion focused on the possibilities mentioned above are key to resolving this.
