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U-joints - what makes them fail?
Universal joints (U-joints) are exposed to tremendous forces. They
help transfer power and torque from the motor to the wheels. Part
of the job of a universal joint is to allow flex in the driveline
to compensate for various driveline angle changes due to increased/decreased
cargo weight, bumps and other suspension flex. Below are common
reasons why universal joints fail:
1. Lack of regular lubrication
U-joints require regular lubrication, about every oil change. Regular
lubrication helps flush out degraded grease and contaminants like
water and dust. Lack of regular lubrication is the number one reason
u-joints fail. Many vehicles
come with non-greasable universal joints that can't be greased regularly.
If you are replacing your vehicle's universal joints, be they are
greasable
2. Contaminants - water, dust,
dirt
Trucks and SUVs are more likely to be used in conditions where they
often come into prolonged contact with contaminants such as water,
dust and dirt. Universal joints' seals do a good job keeping contaminants
out for the most part, however, continued exposure and rough conditions
may allow some contaminants to enter. Water is particularly susceptible
since universal joint seals are not designed to be waterproof under
heavy exposure like crossing streams. When water enters the u-joint
it degrades the grease's lubricating capacity and increases wear.
If you cross streams frequently it's a good idea to grease u-joints
after each crossing.
4. Heavy loads
Towing heavy loads puts increased stress and strain on universal
joints which increases wear
5. Driveline irregularities
Below is a list of driveline problems which can greatly reduce the
lifespan of universal joints.
Unbalanced driveshaft - Driveshafts spin at high speeds and are
balanced at the factory. If a driveshaft becomes slightly bent or
a weight falls off (due to rust or off-road encounter with a deep
rut or branches) the driveshaft will begin to vibrate and prematurely
wear the u-joint. Often, these vibrations are subtle and difficult
to feel in the cabin.
Bent rim or unbalanced tire - sends vibrations through the driveline
to the driveshaft. Mud on the backside of a rim where it is not
visible can cause a tire to be unbalanced enough to cause damage
after time.
Incorrect driveshaft angle - Aftermarket
lift kits installed on trucks or SUVs change the driveline angle
and put increased stressed on universal joints. In addition, a slight
lift of a couple inches can also create driveline vibration.
Loose driveshaft mounting flange
Any other unusual driveline vibration.
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