What Is a Universal Joint?
Universal joints are X-shaped parts typically made of steel with a bearing cap at each end. These joints enable the rigid driveshaft of the car to be connected to the transmission and move freely.
They are part of the system that enables the rotating crankshaft in a vehicle's engine to transfer that rotating motion to the rear wheels in a rear-wheel-drive vehicle. They enable the driveshaft to move up and down and at an angle to the engine when the car encounters uneven road surfaces because they offer a flexible connection at the driveshaft's ends.
There are universal joints at both ends of driveshafts, for instance, in pickup trucks. These u-joints are usually connected to yokes that permit a driveshaft's fore-and-aft movement as well as the up-and-down movement for which the universal joints compensate. A vehicle could not have a suspension system that provided any significant wheel travel without universal joints or a system similar to it; otherwise, the driveline would bind at every bump and pothole.
Front-wheel-drive vehicles have constant velocity joints, or CV joints. They perform a similar function to universal joints.
What Does a Universal Joint Do?
Vehicles do not travel on surfaces as flat as a billiard table; therefore, driveshafts need to be able to rotate and move up and down with the suspension to keep power flowing to the drive wheels. The driveshaft can continue to turn while this movement is made possible by the universal joints.
The height mismatch between the rear axle that drives the rear wheels and the transmission is compensated for by the use of U-joints. A direct driveshaft from the engine to the axle would bind or bend when the vehicle encountered bumps because the rear axle and wheels of a vehicle move independently of the rest of the vehicle. The driveshaft continues to rotate freely because the u-joints compensate for that motion. The u-joints' flexible "universal" action automatically corrects misalignment as the driveshaft rotates.
What Maintenance Is Necessary?
It is evident that whenever the car is in motion, its universal joints receive significant use. The intensity of the workout increases with the vehicle's speed and the rear axle's up-and-down movement. This implies that U-joints need to be maintained.
The bearings of each U-joint are greased at the factory during assembly. Certain lubricants are "lubed for life," meaning that extra lubricant cannot be added to maintain them. Grease fittings on other universal joints enable the addition of grease as necessary.
In either type, the lubrication can diminish over time, and the "dry" bearing results in wear-causing metal-to-metal contact. You can lubricate universal joints with a grease fitting, but U-joints without that ability will simply wear out and need replacement. Happily, their service life is quite lengthy.
What Are Symptoms of U-Joint Failure?
In the worst-case scenario, the driveshaft could detach from the car, seriously damage it, and possibly result in an accident. For this reason, it is advisable to pay attention to any indications that your vehicle's universal joints are malfunctioning. Worn u-joints have the potential to cause expensive transmission problems and leave you stranded on the side of the road even before they completely fail.
Here are some early warning signs of U-joint failure:
· Squeaking noise when moving from a standstill
· Clunk sound when shifting
· Vehicle vibration when underway
· Fluid leaks from the back of the transmission
· Banging sound accompanied by complete loss of power
What Should You Do?
If you think your vehicle's u-joints are nearing the end of their useful life, have them replaced as soon as possible. The repair is not very costly and is far less expensive than the repairs required if you ignore them and suffer transmission problems or a driveshaft separation.
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