Driveshaft Vibrations
There are generally four types of driveshaft vibrations.
- Transverse Vibrations – are typically the result of an unbalanced driveshaft. A transverse vibration will occur once per every revolution of the driveshaft. This could be because of damage to the shaft, missing balance weights or foreign material stuck to the driveshaft.
- Torsional vibrations – occur twice per revolution of the driveshaft. They could be due to excessive u-joint angles or a shaft not in phase with its design specifications. A yoke outside of its design phasing by just one spline can cause torsional vibration issues.
- Critical speed vibrations – occur when a driveshaft operates at an RPM too high in relation to its length, diameter and mass.
- Component failure – of the driveshaft or the motor and transmission mounts can cause vibration. A failing u-joint is a prime example.
Driveline Failures
There are many different causes behind the failure of various driveline components. A few of these can be the cause of failure for multiple components of a driveshaft. The following are key terminology to common driveline failures.
Shock Load is a sudden force applied against a driveline component. It is also the most common cause of failure. Extremely cold temperatures can facilitate a failure due to shock load. Several often seen causes are:
- Driving into an immovable object under power
- Tires that suddenly grab after spinning on a slick surface
- A sudden attempt at pulling an immovable load, such as a trailer with frozen brakes
- Popping the clutch at higher than normal RPM
Excessive Torque Load, also known as torsional fatigue, is a prolonged force applied against a driveline component at greater than recommended specs. Excessive torque is usually the result of pulling a heavier load than rated for the vehicle.
Improper Application is where the driveline components installed are not in-line with the vehicle specs or its purpose.
Surface Fatigue or contact fatigue, is a general term for several different damage types that can manifest on the load bearing surface of driveline components, including:
- Brinelling
- Spalling
- Galling
Critical speed is the point at which a driveshaft operates at an RPM too high in relation to its length, diameter and mass.
Twisted Tubing
Causes:
- Shock load
- Excessive torque load
- Improper application
End Galling
End galling, or galling, is a type of surface fatigue that is characterized by marring on the flat surface at the end of the u-joint cross.
Causes:
- Greater than recommended u-joint operating angles
- Improper assembly
- A sprung or damaged yoke
- Lack of lubrication
Spalling
Spalling, another type of surface fatigue, occurs when the bearings inside of the u-joint bearing cap do not move freely. This in turn causes the bearings to grind against the cross, wearing grooves across the surface.
Causes:
- Water or dirt contamination
- Improper lubrication type
- Lubrication failure
- Excessive load over a prolonged duration
- Operation above maximum mileage specifications
Brinelling
Brinelling is the result of the bearings inside of the bearing cap stamping into the outsides of the u-joint cross.
Causes:
- Continuous excessive torque loads
- Seized slip yoke splines that do not allow the shaft to adjust in length
- Greater than recommended u-joint operating angles
- Improper application
- A sprung or damaged yoke
- Improper or lack of lubrication
Burned U-Joint Cross
The same occurrences that cause brinelling and spalling can also cause a higher degree of damage that actually burns out the u-joint cross.
Causes:
- Lack of lubrication
- Improper maintenance
- Wrong lubrication type
- Improper application
Fractured Yoke
Causes:
- Excessive torque loads
- Shock load
- Improper Application
- U-joint failure
- Improper installation
Bent/Sprung Yoke
With a sprung yoke, where the bend is within the ears of the yoke, the bend can be imperceptible at a glance and may only be noticed when replacing a u-joint. When installing the new u-joint, the crosses will not be centered through the holes of the yoke on both sides.
Causes:
- Excessive torque loads
- Improper application
- Improper u-joint removal
- Improper operating angles
- Thrown driveshaft
- Improper installation
- Improper maintenance
Broken Tang Half Round
Causes:
- Improper bearing retainer bolt torque
- Improper installation
- Re-use of the bearing strap
Broken Tube Weld
Causes:
- Shock load
- Improper welding procedure
- Attachment of the balance weights too close to the weld
- Excessive vibration
Fractured Spline
Causes:
- Shock load
- Excessive torque
- Improper application
For Additional Assistance Refer To Spicer Driveshaft Components Failure Analysis Guide