Contents: Noise localization ↧ Definition of noise in motion ↧ Noises in the gearbox ↧ Bearing noise ↧ Other noises ↧
Noise localization
Before attempting to repair the clutch or transaxle assembly, determine the cause of any noise.
Signs of a faulty clutch or manual transmission:
- Increased effort required to shift gears.
- The metallic clanking of gears when shifting.
- Gear lock.
If any of the above symptoms occur, a thorough analysis of the fault is necessary. Before disassembling the clutch or gearbox, the following checks must be carried out.
Definition of noise in motion
Many noises that at first glance appear to come from the gearbox actually have other sources, such as:
- Tires.
- Road surface.
- Wheel bearings.
- Engine.
- Exhaust system.
These noises may vary depending on:
- Dimensions of the car.
- Type of car.
- The amount of soundproofing material used in the car.
Noises in the gearbox
The gearbox, like any mechanical device, is not absolutely quiet and produces a certain noise during normal operation.
To identify suspicious gearbox noises, it is necessary:
1. Choose a level section of road to reduce tire noise and body vibrations.
2. Drive a distance long enough to warm up the oil.
3. Note the speed and gear at which the noise occurred.
4. Check for noise with the vehicle stopped and the engine running.
5. Determine in which driving modes the noise occurs:
- In acceleration mode.
- In constant speed driving mode (the throttle valve is slightly open, the car is moving on a flat road without a slope).
- In coasting mode (Gearbox at speed, throttle valve partially or fully closed).
- In all the modes described above.
Bearing noise
Noise from differential side bearings
The noise coming from the differential side bearings and the wheel hub bearings are very similar. Since the side bearings are preloaded, the noise coming from them should not be significantly reduced if the transmission and differential are running on a raised vehicle (the wheels do not touch the road).
Wheel hub bearing noise
The wheel bearing produces a specific grinding noise, which is also heard when the car is coasting with the gear in neutral. Since the wheel bearing is assembled without preload, the noise emanating from it should be reduced if the car is lifted (the wheels do not touch the road).
Other noises
Formation of dents on the rolling surfaces of bearings (brinelling)
The brinellated bearing is the source of a knocking sound that occurs once every two wheel revolutions, which is explained by the difference in the speed of the wheel and the bearing elements. When the car is moving, the bearing knock is perceived as a low-frequency noise.
Bearing knocking occurs due to the formation of dents in the bearing race from balls under the effect of excessive load. Bearing brinelling can also occur if, when pressing in one ring, pressure is simultaneously applied to the second bearing ring.
Vibrations in the area of the bearing installation may be mistaken for bearing knocking. A sign of brinelling is the presence of dents on the rolling surfaces of the bearing.
Bearing wear
Bearing wear can occur when abrasive particles, such as scale, sand or emery with oil, enter them. As a result, the rolling surfaces wear out. Bearing wear, which at the same time operates without impacts and does not have cracks or corrosion pits, is a consequence of oil contamination.
Blocking
Large particles of foreign material caught between the balls and the bearing ring often cause the bearing to lock and one of the rings to spin, causing noise. Excessive preload on a tapered roller bearing can also cause the bearing to lock.
Pitting corrosion
The formation of cavities on the rolling surfaces is a consequence of normal wear and tear and the ingress of foreign particles.
Painting
This bearing defect is characterized by material peeling or pitting on the surface of the balls or rings as a result of overloading or improper assembly, which may result in improper adjustment, misalignment, or increased friction in the bearing.
After completing the above checks, proceed to the "Diagnostic Cards" subsection in this section.