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U Joints and CV Joints


There are two important parts on RWD and FWD vehicles that serve a similar purpose. CV Joints and U Joints. For Front Wheel Drive (FWD) Vehicles, the CV Joints are used in independent drive axle assemblies to allow for the shaft to have some movement and keep the torque being transferred to the drive wheels smoothly. The inboard CV Joint is a sliding tripod joint that allows for up and down movement of the wheels as they travel over bumps in the road and also some allowance for the change in drive axle length with extreme suspension movement.  The plunging action of the CV joint accommodates the change in distance between the transaxle and the wheel hub.  The outboard CV joint is normally a fixed joint at the wheel hub that transfers power to the wheel while allowing the wheel to be turned for cornering.  The CV Joints are covered by a boot which is a flexible synthetic rubber balloon seal.  This seal keeps road dirt out of the bearings and helps to prevent loss of lubricant while high rotating speeds and centrifugal forces are trying to fling the grease out of the joint.  Each axle boot provides a dust, water, and grease seal that is important to the longevity of the CV Joint. 

Front drive axle problems are usually noticed as abnormal noises like a clicking when turning sharply, vibration, or excessive play in joints. Drive axles are under stress from high engine torques being transferred at various angles through the driveline.  This can cause the CV Joint bearings and races to fail after prolonged use.  If the rubber boot around a CV Joint is ruptured, road dirt and water will enter and wash the grease out of the joint.  Contamination and lubricant loss will quickly cause joint wear and failure.

On Rear Wheel Drive (RWD) Vehicles the driveshaft connects the transmission to the rear differential.  Universal joints or U Joints, are used to allow the shaft to move as the differential moves up and down.  A worn universal joint, the most common drive shaft problem, can cause a vibration or squeaking, grinding, clunking or clicking sounds. The grease inside the joint can dry out.  The roller bearings can then wear grooves in the joint cross.  When the bearings try to roll over these grooves, a loud metal-on-metal grinding or chirping sound can result.  Quite often, a worn U Joint will be heard when the vehicle is in reverse gear.  When the vehicle is backed up, the roller bearings are forced over the wear indentations against the normal rotation and the rollers will catch on the sharper edges in the worn joint and cause the sound to be even louder.   Also U joints can produce a groaning noise/vibration heard or  felt in the seat usually when on the highway. Sometimes the U-Joints can be visually inspected for damage, but many times, the drive shaft itself may have to be removed to inspect the joints fully. 

A Technician will need to test drive your vehicle and then put it on a lift to fully inspect these parts.  U joints and Boots on CV Joints need to be fully visually inspected as well as manually moved and rotated to check for excessive play and wear. 

Give Jammin’ J Auto a call today to schedule an appointment if you are hearing any noises from under your vehicle or feeling any vibrations when driving.

 

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