Drive shafts are critical components of a vehicle's drivetrain system, responsible for transferring power from the engine to the wheels. Universal joints (also known as u-joints) are an integral part of the drive shaft, allowing it to flex and move as the vehicle's suspension changes. However, universal joints can break or wear out over time, leading to a number of issues. Here are some of the most common causes of u-joint failure:
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Overloading and Overworking the U-Joint: Overloading and overworking the u-joint can occur in a variety of situations, and one of the most common is running too large of tires for the size of the drive shaft. Bigger tires take more effort to turn, and the drive shaft needs to be upgraded accordingly to handle the increased stress. If the drive shaft is not upgraded when larger tires are added, it can cause u-joints and other parts of the drive shaft to break.
Similarly, if a vehicle is used for heavy-duty or off-road applications without upgrading the drive shaft and u-joint components, it can also lead to premature wear and eventual failure. If the vehicle's engine or transmission is upgraded without upgrading the drive shaft and u-joint components, it can cause excessive stress on the joint and lead to failure.
In general, it's important to ensure that the drive shaft and u-joint components are properly matched to the vehicle's application, whether it's heavy-duty work, off-roading, towing, or running larger tires. Failure to do so can lead to premature wear and eventual failure of the u-joint.
Poor Maintenance: Another common cause of u-joint failure is poor maintenance. Over time, u-joints can become contaminated with dirt, debris, and moisture, which can cause corrosion and wear. Regular maintenance, such as greasing the joints and inspecting them for damage, can help prevent this type of wear and tear.
Angle: Drive shafts and universal joints are designed to operate within a certain range of angles. If the angle of the drive shaft is too steep, it can cause excessive stress on the u-joints, leading to wear and eventual failure.
Over-Flexing and Binding: Another common problem that can cause u-joint failure is over-flexing and binding. This can occur if the drive shaft is running at too steep of an angle under full suspension droop or if there is axle wrap in a leaf-sprung vehicle with a spring-over conversion. When the u-joint is over-flexed, it can bind, causing excessive stress on the joint and leading to wear and eventual failure.
To check for signs of over-flexing, look for marks where the yokes of the drive shaft may have come in contact with each other. These marks may appear as shiny or polished areas on the yokes where they have rubbed together. If you notice these marks, it's important to address the cause of the over-flexing and binding to prevent further damage to the u-joint. This may involve adjusting the suspension or driveline angles or installing anti-wrap devices to prevent axle wrap.
Damaged or Worn Out Yokes: The yokes that attach the drive shaft to the transmission and differential can also be a source of u-joint failure. If the yokes become damaged or worn out, it can cause the u-joint to wear out prematurely. Regular inspection of the yokes and replacement as needed can help prevent u-joint failure.
Brinelling
Brinelling is when needle marks appear on the surface of the U-joint cross, which is usually caused by excessive torque, driveline angle. It can also be caused by a seized slip yoke or by a sprung or bent yoke
If you have changed engines or transmissions, calculate the torque transmitted by the new combination.
Your drive shaft series may be too small.
Universal Joint Brinelling
Universal Joint Brinelling w/ Galling
Universal Joint Brinelling
Industrial Joint Brinelling
Spalling
Spalling looks like the bearing surface of the U-joint has been “scraped” away.
Spalling is usually caused by water or dirt contamination
Universal Joint Spalling
Burned U-joint cross Trunnions
Improper lube procedures, where recommended purging is not accomplished, can cause one or more bearings to be starved for grease.
Always make sure new, fresh grease is evident at all four U-joint seals.
Burned U-Joint Trunnion
Burned U-Joint Trunnions
Burned U-Joint Trunnions
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Burned U-Joint Trunnions
End Galling/Galling
The end of the trunnion (of the U-joint cross) looks like material has been “gouged” out.
Usual cause: Operating angles are too large.
Universal Joint End Galling
Industrial U-Joint Galling & Brinelling
Industrial Joint Galling
U-joint Fractures
U-Joint fractures are usually caused by a shock load, but can also be caused by an improper application.
Calculate the torque transmitted by the engine/trans combination. Check to make sure the drive shaft series is not too small for the application.
Universal Joint High Torque Fracture(s)
Universal Joint High Torque Facture
Universal Joint Fracture
Universal Joint Fracture
Improper assembly procedures
Striking the bearing plate with a hammer can cock it on the bearing and may cause the bearing to be pulled down crooked in the yoke. Cocking the bearing in the bore of the yoke may put undue loads on the cross, its bearings and the seals inside those bearings, which may cause premature failures and make proper lubrication difficult.
Bent or deflected end fitting
Bent yokes will put abnormal loading on the U-joint bearings and lead to premature failure. A yoke can be bent by a shock load or by over torquing the yoke.
Weld Yoke Failure
Weld Yoke Failure
Weld Yoke Failure
Mixing incompatible greases
All greases are a mixture of different additives and thickeners. Mixing greases from different manufacturers can lead to a mixture with a lower service performance than either of the original grease products.
Thorough purging of all four bearing seals on each universal joint can help alleviate the possibility of mixing incompatible greases.
U-joints seldom break off at the bearing surface. It takes a very large shock load to cause this type of failure. It is also very difficult to inspect for this type of failure because they, many times, start as a small crack and progress into a complete failure some time further “down the road”.
Operating angles that are too large
Large U-joint operating angles can be caused by improper drive shaft installations, (Vehicle owners sometimes make changes to the original vehicle that can mess up operating angles) a sagging suspension or even improperly adjusted air bags.
Keeping angles small and within recommendations will help to reduce wear on U-joint components and help to lower the chances of having inertia and secondary couple vibration problems.
Operating angles are NOT cancelled
Proper cancellation reduces the chance of having torsional vibrations.
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