There are several possible causes of vibration in a car. Vibrations can arise from the wheels, brakes, suspension, drive shaft or engine. A vibration that occurs at a certain speed is typically associated with the wheels, the driveline or the suspension. While not often dangerous, noticeable vibration is not normal and you should identify and rectify the problem to avoid damaging the car.
Most often vibration at a certain speed is caused by a wheel which is out of balance. These vibrations typically occur at speeds in excess of 45 mph. Wheel balancing problems can be easily diagnosed and fixed by a professional. Damage to the rims or a build up of mud or dirt on a portion of the rim can cause an imbalance. A simple visual inspection can identify such a problem.
The driveline, which includes the drive shafts, axles, joints and differentials, should be considered as the next possible cause of vibration at a certain speed if wheel imbalance has been ruled out. Driveline vibrations can occur when the natural frequencies of shafts or axels are excited during driving. This phenomenon is called resonance. “Tuning” weights are attached to components when the car is manufactured to dampen these vibrations but are sometimes missing which can result in vibrations occurring at certain speeds.
CV joint damage
If the vibration seems worse when accelerating through a corner the culprit may be the continuous velocity or CV joint according to Paul Weissler of Popular Mechanics. The CV joint is located near the wheels and can be identified by its rubber boot. Check the boot for damage or leaking grease and if any is visible consult a professional for further advice.
Worn wheel bearings
Worn wheel bearings can also result in vibrations. To check for wheel bearing damage jack up the car, and grasping the wheel first at its sides and then at its top and bottom, rock the wheel in and out says Weissler. If there is any play then it is likely that the bearing is worn and needs to be replaced.
Worn suspension components
Worn components in your car's suspension can also result in vibrations at certain speeds. Worn bushes and couplings result in play between componets causing vibration. Worn shock absorbers can lead to noise and vibrations and are dangerous as they reduce braking and handling performance.
Other types and causes of vibrations
Vibrations when braking may be a results of warped brake disks. Vibrations that occur during acceleration is typically associated with a driveline problem while one that is related to rpm is normally an engine problem.