A CV Axle is the drive axle on a PORSCHE 928 that contains two
constant velocity joints. CV axle shafts are mainly used in front wheel drive and all
wheel drive cars. However, rear wheel drive cars with independent rear suspensions
typically use CV rear axle halfshafts. Some all wheel drive vehicles use CV axle shafts
for all four axles. Two different types of CV joint are used on CV axles in modern cars.
At the "inboard" end, where the shaft only moves up and down with the movement of the
suspension, a "Triax" (also known as "Tripod") joint is used. This has a three-pointed
yoke attached to the shaft, which has barrel-shaped rollers on the ends. These fit into a
cup with three matching grooves, attached to the differential. Since there is only
significant movement in one axis, this simple arrangement works well.
At the outboard end of the driveshaft, a slightly different unit is used. The end of the
PORSCHE 928 CV Axle is splined which fits into the outer joint and is typically held
in place by a circlip. The shaft fits in the center of a large, steel, star-shaped gear that
nests inside a circular cage. The cage is spherical but with ends open, and it typically has
six openings around the perimeter. This cage and gear fit into a grooved cup that has a
splined and threaded shaft attached to it. Six large steel balls sit inside the cup grooves
and fit into the cage openings, nestled in the grooves of the star gear. The outer shaft on
the cup then runs through the wheel bearing and is secured by the axle nut
The Constant Velocity Joints in a CV axle allow a rotating axle shaft to
transmit power through a variable angle, at constant rotational speed, without an
appreciable increase in friction or play. The CV joint in the CV axle is extremely
flexible, and can accommodate the large changes of angle when the front wheels are
turned by the steering system.
The only maintenance required on PORSCHE 928
CV axle shafts are periodic inspection of the rubber boots that contain the grease to
lubricate the CV joint. Check these boots for damage, cracks will allow the grease to
leak from the boot and dirt to enter the boot causing damage to the CV axle shaft. It is
best practice to replace the complete CV axle shaft if the boot or CV joint fails
A clicking noise when turning sharply at low speed is a symptom of
a failing CV joint in the CV axle shaft. Cracked and grease leaking from CV boots.
Ignoring these symptoms can lead to total CV joint failure rendering the
Half Shaft, Constant Velocity Axle
On front wheel drive vehicle the CV axle is located between the wheel hub
and transaxle or transmission. On vehicles with rear independent suspension the CV axle
is located wheel hub and rear differential.
Depending on the year and options your PORSCHE 928 has, the
above information may not apply. Consult with a professional automotive
technician or manufacturer for specifics on your PORSCHE 928