A universal joint allows a drive shaft on a vehicle to operate at constantly changing angles as the vehicle travels down the road. Rear-wheel drive and four-wheel drive of all kinds have been using universal joints for decades. The universal joint contains small bearings that are subject to wear and failure, so knowing how to diagnose a universal joint problem can prevent getting stranded on the side of the road and facing an expensive tow bill.
Diagnosis: Inside the Vehicle
Get into the driver's seat of the vehicle. Start the vehicle.2
Push the brake pedal down and hold it to prevent the vehicle from moving.3
Move your transmission gear selector into the Drive position and listen for a "clunk" sound. Move the gear selector directly to the Reverse position and listen for a clunk. Moving the gear selector between Drive and Reverse twists the universal joint in opposite directions, so if there is any looseness it may produce an audible clunk sound. Repeat this test as needed. This test will only work with an automatic transmission, not with a manual transmission.4
Drive the vehicle around the block and listen for unusual noises such as squeaking or clunking. Also pay attention to vibrations while moving down the road or shuddering when accelerating from a stop. Any of these things can indicate a universal joint problem, and you should proceed to an under-vehicle inspection.
Diagnosis: Underneath the Vehicle
Set the parking brake on your vehicle and place wheel chocks on one of the rear tires, one in front and one behind, to prevent the vehicle from moving while you're performing the inspection.6
Place the jack underneath the front of the vehicle. Locate a safe point on the vehicle to place the jack and raise it up far enough so you can fit underneath the vehicle and have plenty of room to access the drive shaft. Once the vehicle is high enough, place jack stands underneath the frame rails in the front, and lower the weight of the vehicle onto the jack stands so that the jack is not supporting the vehicle any longer. If you have an SUV or truck and can fit under the vehicle without jacking it up, skip this step.7
Crawl under the vehicle from the side, right around the midpoint of the vehicle. Bring your trouble light or flashlight with you, and use a creeper or ground cloth to keep clean.8
Locate the drive shaft. It is a long, straight metal tube that extends down the center of the vehicle from the rear of the transmission to the rear differential. On both ends of the drive shaft will be the universal joints. They look like a four-pointed cross, with two fingers from the drive shaft holding on to two points of the cross, and fingers from the rear differential or the transmission holding the other two points.9
Position yourself close to the universal joint on the front of the drive shaft, closest to the transmission. Grab the drive shaft with your hand and twist it back and forth. Using your light, watch the universal joint closely. It should be tight, and you should not see any movement or looseness. Repeat this procedure at the universal joint on the rear of the drive shaft. If you detect any movement or looseness at either universal joint, you should have them repaired or replaced.