Mechanics

Vibration

Car Moving: This section includes symptoms that present themselves when the car is in motion

Checking the Tire Wear Pattern - A tire with a scalloped pattern on the tire will cause a vibration sound at speeds over about 45 MPH. This tire condition is caused by a combination of worn struts or shocks and or tire imbalance. If a tire is not being controlled evenly the tire will vibrate causing the tread to contact the ground inconsistently. This inconsistent contact with the road causes the tires tread to wear unevenly. (Cupping, tire example on the right). To check for this condition, take your hand and pass it over the tire tread, it should be smooth. If high and low points exist the tire is cupped and needs to be rotated or replaced depending on the severity of the cupping condition.

Tire Wear Patterns
Tire Wear Patterns

Checking Axle Bearing Failure - An axle bearing is designed to support the weight of the vehicle while allowing the wheels to rotate. These bearings are manufactured with high grade steel that resists wear under extreme conditions. When an axle bearing fails it allows metal to contact metal under pressure with a linear motion creating a vibration noise. Once an axle bearing fails it cannot be repair, replacement is required. Remove axle bearing and replace with new and recheck. Some vehicles are equipped with a bearing hub assembly. The bearing below is the style of bearing is replaced by un-bolting the bearing hub assembly and replacing it with new.

Axle Bearing Hub
Axle Bearing Hub

Other bearing designs include separated bearings that include inner and outer bearings with bearing races, a four piece set. Separated bearings require an inboard seal attached to the bearing hub. This seal rides on the spindle to hold grease inside of the bearing hub, keeping lubrication inside of the bearings.

Axle Bearing/Race Set with Seals
Axle Bearing/Race Set with Seals

Drive Shaft U Joints - A driveshaft universal joint is designed to act as a rotating junction that can be flexible while still transferring energy from the engine to the rear differential. A universal joint or U joint is constructed of 4 bearing caps that house multiple needle bearings. The universal joint is lubricated by adding grease through a zirk fitting on the joint. Some u joints are manufactured with a proper amount of grease and do not need service and therefore do not have a service fitting. If a universal joint fails it can make a vibration noise that contours the motion of the car. To check for this condition inspect the universal joint and look for a light rust powder around the bearing cups. This rust colored powder is caused by metal disintegrating and is a sign of universal joint failure. When a universal joint has failed it must be replaced and cannot be repaired.

Universal or
Universal or "U" Joint

Automatic Transmission Fluid - An automatic transmission functions by automatically changing the gear ratios while determining the speed and load of the engine. A torque converter utilizes transmission fluid as a coupling agent allowing the engine to run while the car is stopped without stalling the engine, then re-engaging to make the car move again once the RPM of the engine has increased. If the transmission is low on fluid due to a leak or service it can cause the transmission to vibrate. If the transmission is vibrating the first thing to do is inspect the transmission fluid level and condition of the fluid. If the fluid level is ok try servicing the transmission. If the condition continues the transmission could need replacement or rebuilding.

Transmission Fluid Level Indicator
Locate and Remove the Transmission Fluid Level Indicator

Testing Check Front Drive Axle CV Joints - When CV joints start to wear they will bind up on acceleration and in tight turns. This causes a vibration in the front suspension that transfers to the vehicle. Remove drive axles and inspect flexibility of each CV joint. If a bind or hard spot is observed the CV Joint/Axle needs to be replaced.

Front Wheel Drive Axle
Front Wheel Drive Axle

Checking Power Steering - A power steering system is designed to utilize power from the engine to assist in the force needed to steer the vehicle. When the engine is running, a serpentine belt is used to transfer engine power to a hydraulic fluid pump. This pump pressurizes fluid and then transfers this fluid using power steering hoses that are connected to a power steering box or rack and pinion depending on how the car is designed. When the power steering system has run low on fluid it can create a vibration. This noise is more apparent when steering the car. When the power steering is malfunctioning the vehicle will be very difficult to steer. It is advised not to move a vehicle with the power steering system not operating properly. Any steering component malfunction can cause the vehicle to be uncontrollable. When a malfunction occurs check the system fluid level and add as needed. When this condition occurs the power steering system has a leak and needs to be inspected and repaired. If the system fluid level is in the normal range and the problem persists the steering rack or pump might need replacing.

Power Steering Cap
Power Steering Cap

Check for Front Brake Rotor Run Out - Front brake rotors can warp when in heavy use. This is caused by extreme heat created by friction and pressure applied to the front brake pads and rotors. A heavy braking condition can be caused by driving down a long grade or extreme driving conditions such as racing. When a brake rotor becomes warped it will cause the steering wheel to vibrate when the brakes are applied. To inspect for this problem rotate the brake rotor by hand. The brake rotor should move freely, but with some resistance and turn for 360 degrees without hard spots. If the brake rotors are warped it is recommended to replace them. It is possible, but not recommended to re-machine to the rotor (the rotor will be straight but it will have less mass to dissipate heat therefore re-warping is eminent).

Front Brake Rotor, Brake Pad and Brake Caliper
Front Brake Rotor, Brake Pad and Brake Caliper

If further assistance is needed, our certified car repair technicians are ready to answer your car questions. Also, gain manufacturer specific instructions and information by clicking - Auto Repair Manual

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AUTHOR


Written by
Co-Founder and CEO of 2CarPros.com
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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Article first published (Updated 2013-08-16)