Diagnosis of Chassis Abnormal Noises in Several Cars
Source: Bearing Network | Time: 2013-02-12
When diagnosing abnormal noises from the chassis of a vehicle, it's important to follow a systematic approach. Start by driving the car on a flat surface for a while to allow the rear axle to reach normal operating temperature. Then, drive until the unusual noise occurs and note the speed at which it happens. After parking, shift the transmission into neutral and gradually accelerate until the engine speed matches the speed when the noise was heard. Check if the noise persists and repeat this process several times to determine whether the sound is related to the engine or other components.
Tire noise and rear axle noise can vary depending on road conditions. Typically, tire noise remains constant, while rear axle noise may only be noticeable at higher speeds—usually above 48 km/h. When driving or coasting, the tire noise stays consistent, but the rear axle noise changes, making it easier to distinguish between the two.
The noise from a faulty hub bearing differs from that of a rear axle. While the front wheel bearing noise remains constant during travel, applying light braking can reduce the load on the bearing, thereby reducing the noise. This helps identify the source of the problem.
At speeds above 48 km/h, rear wheel bearing noise is rarely heard unless there is severe damage. However, when coasting or in neutral, a cracked rear wheel bearing might produce a "long-halogen" or "shasha" type of sound. The differential gears and bearings often emit a sharp, squeaky sound that varies with the vehicle's speed.
The cone-shaped automatic gear front bearing produces more noise during coasting, while the rear bearing becomes louder when the car is in motion. The noise from the differential bearing is usually a steady, sharp sound, but its rhythm is smoother compared to the reducer cone gear bearing.
During straight-line driving, the rear axle gear noise is typically not present because the differential half shaft gear and planet gear have minimal relative motion. However, if the noise is heard at various speeds, it may indicate issues such as improper tightening of the automatic gear nut or worn-out gears due to poor smoothness.
At low speeds, knocking sounds from the rear axle may occur when accelerating or decelerating. These noises are often distinct and irritating. Common causes include:
1. Improper clearance between the differential half shaft gear journal and the differential case.
2. Inappropriate fit between the differential cross shaft journal and the differential case.
3. Incorrect backlash between the half shaft spline gear and the differential half shaft gear keyway.
4. Improper meshing clearance between the differential half shaft gear and the planetary gear.
5. Inappropriate gap in the differential cone gear and forced gear meshing.
6. Worn thrust washers.
If the abnormal noise from the rear axle is caused by gear meshing gaps or improperly adjusted differential bearing preloading, disassembling the differential gear is necessary. Checking the meshing clearance of the reducer gear, the preload of the reducer cone gear bearing, and the contact marks of the reducer gear is essential for proper diagnosis and repair.
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