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How
Does it Work /
U Joint
How a "U" Joint Works
Introduction:
A "U" joint is named after the style of coupler used to create the joint. Shafts
involved are fitting with a "U" style of coupler that is connected by an "X" member
(U joint) with bearing on each of the four ends. These bearings allow the "U" joint
to operate under extreme load. Grease is used to lubricate the joint they can either
be installed by a pressurized grease gun or by the manufacturer when the U joint
is assembled. This joint allows the shafts to be connected while axis's pivots
change, for example: when suspension operation occurs. A typical "U" joint has grease
seals on each bearing cap so a boot is not needed like a
CV joint.
A "U" joint is much like the CV joint in that it doesn't require service unless
fitted with a zirk fitting meant to allow grease to be inserted.
Typical U Joint Configuration Illustration
There are other types of flexible couplings such as a Thomas or Oldham joint.
These joints use a rubber fiber flex material and are mainly used for low power
applications. Sometimes, when replacing a "U" joint you may need to replace the
axle assembly depending on the design of the car. Some manufactures allow the joint
to be replaced separately; you will need to check with a part supplier to inform
you on which type your car has. When a "U" joint fails it can cause a rapid clicking
or squeaking
noise that occurs when the car is being driven and is usually more audible at
slower speeds. Also, a "U" joint can cause a fine rust colored powder in and around
the "U" joint caps when the joint has failed. This dust is the result of metal contacting
metal with no lubricant under extreme pressure.
Universal or "U" Joint
Replacing a U Joint:
- Support car in a safe position high enough to remove the driveshaft in question
- Loosen appropriate nuts and bolts to remove the driveshaft
- Remove all retainer clips from the inside or outside bearing caps
- Position the shaft in vise to force the primary shaft downward, this will
cause the lower bearing cup to release
- Loosen the vise and turn the shaft 180 degrees and retighten, force the
upper bearing and shaft downward, this will cause the lower bearing to release,
now remove the joint
- Repeat this operation for subsequent shafts or couplers
For manufacturer replacement or service procedures consult a
car repair manual
Common Problems
- When replacing a U joint make sure the needle bearings do not lay down
inside the bearing cup not
allowing the bearing cap to be completely installed
- If a U joint is stiff or has rough spots during operation the U joint has
gone bad and needs replacing
How Does it Work /
U Joint
Check Manufacturer Specific U Joint
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