What is a CV Joint?
A CV joint, or Constant-Velocity joint, is a component in many vehicles, especially those with front-wheel or all-wheel drive. It connects the transmission to the wheels, allowing power to transfer while the wheels move up and down with the suspension and side to side with steering. This helps maintain a steady speed, reducing vibrations compared to older universal joints.
Common Uses
CV joints are commonly found in front-wheel drive vehicles, where they ensure power reaches the wheels despite changes in angle from steering and suspension. They are also used in some rear-wheel drive cars with independent suspension, particularly at the half-shaft ends and increasingly on tailshafts.
Signs of Failure
If a CV joint fails, you might hear clicking or popping noises, especially when turning, which could indicate a worn outer joint. Grease leakage from a damaged boot is another sign, as is lateral shaking or vibration during acceleration, often linked to inner joint issues. Clunking when shifting gears can also occur with a worn inner CV joint.
Definition and Historical Context
A CV joint is defined as a mechanical coupling that allows two shafts to rotate freely without significant friction or backlash, compensating for the angle between them to maintain a constant velocity. This is a significant improvement over universal joints, which can cause speed fluctuations and vibrations, especially at larger angles. The concept of CV joints has historical roots, with early examples like the 1926 Tracta joint, used in vehicles such as the 1931 DKW F1 and 1932 Adler Trumpf, highlighting their long-standing importance in automotive engineering.
The function of a CV joint is to ensure that the rotational speed remains consistent, even as the driveshaft angle changes due to steering or suspension movement. This is achieved through designs that allow for flexibility, such as ball-and-groove mechanisms, which are common in modern applications.
Common Applications and Types
CV joints are predominantly used in front-wheel drive vehicles, where they transfer engine power to the wheels despite varying driveshaft angles caused by steering and suspension operations. They are also increasingly utilized in modern rear-wheel drive cars with independent rear suspension, particularly at the half-shaft ends and on tailshafts. This adaptability makes them versatile for various vehicle types, including passenger cars and light vehicles.
There are several types of CV joints, each suited to specific applications:
- Rzeppa Joints: Commonly found in front-wheel drive cars, allowing articulation angles of 45°–48°, with some designs reaching up to 54°.
- Tripod Joints: Used at the inboard end of car driveshafts, typically in rear-wheel drive or the inboard side of front-wheel drive vehicles, with up to 50 mm of plunge travel and 26 degrees of angular articulation.
- Double Cardan Joints: Often used in steering columns and rugged four-wheel drive vehicles for high articulation angles or impulsive torque loads.
These types cater to different needs, such as the plunging capability of tripod joints for suspension travel or the high articulation of Rzeppa joints for steering movements.
Symptoms of Failure and Common Issues
CV joints can fail over time, and recognizing the symptoms is crucial for timely maintenance. The following table summarizes the common symptoms, their descriptions, and related CV joint types:
| Symptom | Description | Related CV Joint Type |
|---|
| Grease leakage | Grease coming out of a small crack or tear in the CV joint boot, often seen as dark grease on the rim and around the joint. | Both |
| Clicking or popping noise when turning | Noise that gets louder when accelerating in turns, indicating wear. | Outer |
| Lateral shaking or vibration during acceleration | Side-to-side shaking during acceleration, suggesting inner joint failure. | Inner |
| Clunking when shifting | Occurs when shifting from Drive to Reverse or during acceleration/deceleration, due to a worn inner joint. | Inner |
Grease leakage is an early sign of boot failure, which can lead to moisture and dirt entering the joint, causing accelerated wear due to lack of lubrication and corrosion. Outer CV joint boots often fail first due to their exposure to more movement, while inner CV joint failures are rarer but can cause significant vibrations. In severe cases, a disintegrating CV joint can create hazardous driving conditions.
Maintenance and Longevity
CV joints themselves do not require regular maintenance if their protective boots remain intact. The boot, typically made of rubber or plastic and secured with clamps, seals the joint and retains special grease, protecting it from environmental damage. Regular inspections during maintenance visits are recommended, where mechanics check for cracks, tears, or loose clamps on the boot. Early detection of boot damage can prevent premature joint failure, with some vehicles maintaining original CV joints for over 300,000 miles.
Additional Considerations
CV joints are typically found in pairs on each drive shaft, with an inner and outer joint on each side, which can wear out simultaneously, often leading to replacement in pairs. The cost of replacement can vary, typically ranging from $100 to $400 per joint for parts and labor, depending on the vehicle make and model.
