CV joints and U-joints allow the wheels driving the car to move up and down with the suspension. CV joints, which allow for greater movement, are generally used on front-wheel-drive cars and cars with independent rear suspensions.
U-joints are generally used on rear-wheel-drive vehicles and larger four-wheeldrive trucks. Both allow the joint to bend while the drive tubes rotate.
The first step in inspecting the drive joints is to drive the car and listen and feel for problems. Look and listen for the following when driving the car:
1. VIBRATION WHILE DRIVING.
A failing joint may cause vibration at specific speeds. Some U-joints will be smooth at low and high speeds, but start to vibrate around 40 to 55 mph (65 to 80 kph). The vibration may also increase with speed. If you are experiencing a vibration, stop the car and shift into neutral or park and rev the motor to make sure the vibration is not engine related.
2. A CLUNKING SOUND WHEN GOING INTO OR CHANGING GEARS.
If you feel a clunk when the car starts from a stop or when the transmission changes gears, the joints are loosening and wearing, causing the torque of the transmission to slap the loose joint.
3. A POPPING NOISE.
A constant click or pop coming from one of the joints means part of the joint has worn and is catching on each revolution.
4. A GRINDING OR METAL-ON-METAL SOUND.
A joint where the grease has failed will begin to disintegrate and produce a metal-on-metal sound.
There should be no play in a U-joint. You can inspect the joints by trying to turn the driveshaft by hand to see if it moves.
1. RAISE THE VEHICLE
If necessary, raise the vehicle and secure with jack stands in order to access the driveshaft.
2. WIGGLE THE DRIVESHAFT.
With the vehicle in park, try to rotate the shaft. The U-joints should have no play and the tubes should all rotate together. You may see some movement in all the components. Wiggle the driveshaft up and down and side to side to look for movement. Test both ends of the shaft.
3. TEST THE END PLAY.
You can check the end U-joint by gently applying leverage between the joint and the differential with a screwdriver. It should remain firm and not move at all.
INSPECTING CV JOINTS
CV joints are sealed in a protective rubber cover, or boot, and if the boot becomes torn or breaks, the grease inside will leak out. A torn CV boot can be replaced, but it requires some knowledge to do so.
1. RAISE THE VEHICLE.
If you can, raise the vehicle and secure with safety stands so the drive wheel being tested is off the ground. This will allow you to turn the wheels fully to inspect the boots.
2. INSPECT THE BOOT.
Put on protective gloves and run your finger around the boot, feeling between the grooves for grease. Globs of grease indicate that the boot may be torn and is forcing grease out of the tear.
3. ROTATE THE DRIVE AXLE.
With the wheel turned out, put the car in neutral and slowly spin the drive axle to view the entire boot in the open position. The side that is compressed can hide a tear. As you rotate the shaft, listen for grinding or popping noises.
4. WIGGLE THE SHAFT.
As with the U-joint, wiggle the output shaft and look for joint movement. It should be tight.
GREASING A U-JOINT
As part of your normal maintenance, it is good to keep the U-joints greased if they are equipped with a grease fitting. Some heavy duty U-joints are not equipped with grease fitting because they can crack and fail at the fitting. The U-joint is designed to extrude the used grease at the ends, purging the used grease from the joint.
1. LOCATE THE GREASE FITTING.
Raise and safely secure the vehicle if necessary. The grease fitting is a small, ball-shaped nipple with a
valve in the end to keep the grease in. Use a paper towel or clean rag to wipe dirt and grime from the fitting. Also, clean all dirt off the grease gun so no contaminants get pushed into the fitting.
2. ATTACH THE GUN TO THE FITTING.
You should feel the end of the grease gun snap over the fitting.
3. GREASE THE U-JOINT.
Begin pumping fresh grease into the U-joint until you see grease coming out of all four seals. Because this U-joint isn’t in a car, the grease came out of the two cups that aren’t secured. It should come out of all four seals simultaneously.
Once you see fresh grease coming out, remove the grease gun and wipe away the purged grease and the grease around the fittings.