* Driveshaft(s): A worn U-joint in either the front or rear driveshaft is a very common cause of speed-dependent vibrations. U-joints wear over time and cause vibrations at certain speeds. The change in vibration intensity at different speeds is characteristic of this problem. A driveshaft imbalance or a bent driveshaft is also possible.
* Wheel Bearings: While you replaced the tires, worn wheel bearings can cause vibrations, especially at higher speeds. Check all four wheel bearings for play or noise.
* Transfer Case: Problems within the transfer case, such as worn components or low fluid, could contribute to vibrations, particularly in a 4WD vehicle.
* Differential(s): Worn gears or bearings in either the front or rear differential can cause vibrations. A pinion bearing issue in the differential is also a possibility. This is less likely if the vibration changes with speed rather than being constant.
* Balance Issues (despite new tires): While less likely *after* new tire replacement, it's worth considering if the wheels themselves are balanced correctly, or if there is a problem with the wheel weights falling off.
Troubleshooting Steps:
1. Visual Inspection: Carefully inspect the driveshafts, U-joints, and the entire drivetrain for any obvious damage, loose components, or signs of wear. Look for leaks from the transfer case or differentials.
2. Test Drive with Observations: Have someone ride with you to note the vibration's location (front or rear). Does the vibration change noticeably when you shift into 4WD (if applicable)?
3. Professional Inspection: The most reliable way to diagnose this is to have a qualified mechanic inspect your Blazer. They have the tools and experience to identify the source of the vibration more precisely and accurately. They can also check the balance of the wheels and rotating components to rule this out as a possibility.
It's important to address the vibration issue promptly. Ignoring it could lead to more significant damage and potentially dangerous driving conditions. Don't continue driving at high speeds with a persistent vibration.
