Failed or Binding Constant Velocity (CV) Joints
Constant velocity joints allow the shaft connected to the joint to rotate at a constant speed (velocity) all of the time.
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There are two commonly used types of Constant Velocity (CV) Joints:
- Tri-pod joint. A tri-pod joint allows for lateral movement (caused by suspension height changes) of the joint while the joint is rotating. This type of joint is typically found on the inside joint of axle shafts and half-shafts; however, it may be also found on the inside joint or both.
This joint contains a tri-lobal spider bearing assemble similar to a U-joint
cross bearing, but with only four bearing caps that slide laterally in the
CV-Joint housing as well as allows for angle changes.
- Double offset (Rzeppa) joint. A
double offset joint does not allow for lateral movement of the joint while
the joint is rotating. This type of joint is typically found on the outside
joint of axle shafts and half-shafts; however, it may be also found on the
inside joint as well as front or rear propshafts.
Constant Velocity (CV) Joints are used on:
- Front wheel drive vehicles - Axle shafts or half shafts.
- Four-wheel drive vehicles - Front Axle shafts or half shafts.
- Independent Rear Suspension - Rear Axle shafts or half shafts.
- Front and rear axle shafts or half shafts. A CV
half shaft is shown below in the photograph of the front suspension.
- Rear propshaft. A double offset (Rzeppa) CV joint
is shown in the photograph below of a rear propshaft connection to the rear
axle of a 2010 Jeep Wrangler Rubicon. This type of joint can handle larger
operating angles (10 degrees) as compared to U-joints (5 degrees).
Diagnosing CV-Joint Related Vibrations
On front-wheel drive or four-wheel drive vehicles, the axle shafts or half shafts rotate at the same speed as the tires. When there is a failure of a tri-pod CV joint, it can cause a third order tire speed related vibration that is more noticeable while turning. Some CV joint shafts use a double offset joint (Rzeppa Joint) rather than a tri-pod joint. The double offset joint typically has six ball bearings, therefore it will have a sixth order vibration when it has a problem.
- Inspect the shaft and the boots for damage, replace or repair as necessary.
- Remove the shaft and rotate the CV-joint through its full range of motion while feeling for any rough spots or looseness. CV joints have load-bearing sliding surfaces which eventually wear out and cause vibrations.
Vehicle Trim Height and CV-Joint Binding
Axle shaft or half-shaft CV-Joint vibrations can also be caused by the suspension system moving up or down excessively while under moderate to heavy acceleration. This causes the CV joint to bind at its maximum angle limits resulting in a vibration. This will cause a third order tire speed related vibration for tri-pod joints, and sixth order tire speed related for Rzeppa joints. This is usually a result of:
- Worn or failed springs.
- Worn or failed shock absorbers.
- Worn or failed struts.
CV-Joint vibrations can also be caused by incorrect vehicle trim height resulting in improper CV-Joint angles and binding. Vehicles with this type of vibration are:
- Vehicles that are heavily loaded.
- Vehicles that are towing a trailer.
- Vehicles which have modified suspension systems. If the vehicle has been raised with a lift kit or lowered, the vibration may not be totally correctable.
To determine if the vehicle trim-height is incorrect, perform the following steps:
- Make sure the vehicle is on a level surface, such as a alignment rack.
- Remove the alignment rack floating pins.
- Set the tire pressures to the pressure shown on the certification label.
- Check the fuel level. Add additional weight if necessary to simulate a full tank.
- Make sure the rear compartment is empty except for the spare tire.
- Close the doors and hood.
- Inspect, measure and repair the front and rear trim height as necessary.
In the example shown above (2003 Chevrolet 2500 HD 4WD) the Z height should be 4.5 inches.
This page was last modified
Tuesday, November 19, 2013 10:02:23 PM
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