It is most common to find driveshaft u-joints on rear wheel drive automobiles. You may also find them driving the front wheels on 4 Wheel drive models with I beam suspension like on some older Ford trucks.
In some cases this flexible joint will have a grease fitting and will require regular service. In other cases they are sealed from the factory and will require no lubrication at all. Drive-shaft u-joints have been around for a long time.
Common driveshaft u-joint problems
One of the most common signs of a damaged or bad universal joint is when a clunk is heard when the transmission is shifted into gear or moved from reverse to drive. This clunk can be caused by other problems but may be a sign of excessive clearance in the u-joints.
When a driveshaft flexible joint is on its way out it can also cause vibrations at higher speeds. This may feel like a wheel balance problem. A way to tell the two problems apart is in most cases a worn u-joint will cause vibration during acceleration or deceleration. A tire balance problem will create a steady vibration regardless of throttle position.
The road test would be just the first step in confirming a problem with the driveshaft u-joints. It is easiest to inspect the parts with the vehicle up on a lift. When you inspect the universal joint if you see grease leaking out of the end caps this is a sure sign that there is a problem.
With the vehicle raised in the air and the transmission placed in neutral you can usually grab the driveshaft and rotate it to spin the rear wheels. Moving the driveshaft a half turns up and back in either direction is a good way to inspect for looseness. It should have no noticeable play when moving up and back as described.
Removing and inspecting the driveshaft
Before you remove the driveshaft it is a good idea to mark it in relationship to the differential yoke. In some cases a shaft can be specifically balanced. If you remove and reinstall it and a vibration that was not there before surfaces it might be out of phase.
When the driveshaft is removed it is easier to check the condition of the universal joints on both ends of the propeller shaft. You should be able to rock the u-joints in all directions and it should provide smooth steady movement. Any stiffness or bumping that is felt is a sure sign of a defective u-joint.
Although it is not a common problem I have seen repeat universal joint failures and stubborn vibration complaints from drivers that have had undercoating installed on the vehicle. A sloppy undercoat job can get on the driveshaft itself and cause out of balance problems that can have negative effects on the universal joints life.
If you find u-joints with any problems just go ahead and replace it. In most cases they are not expensive. Different manufacturers have different types of joints and therefore different service procedures are needed.
Example: General Motors original universal joints with plastic inserts can be difficult to replace. The Ford universal joints with removable spring clips are much easier. I recommend that you check your online auto service manual for your specific procedure.
Kings Transmission Seattle offers a full line of U-joint repair and replacement. We also will diagnose driveline problems for free.