I. Abnormal noise from the transmission
Abnormal noises from the transmission refer to unusual sounds emitted during transmission operation.
Causes 1) Gear noise: Excessive wear and thinning of gears, excessive clearance, and impact during operation; poor gear meshing, such as not replacing gears in pairs during repair; mismatch between new and old gears, resulting in incorrect gear meshing; metal fatigue spalling on the gear surface or damage/breakage of individual teeth; loose spline fit between gear and shaft, or excessive axial clearance of gears; bent shaft or loose bearing causing changes in gear meshing clearance. 2) Bearing noise: Severe bearing wear; loose fit between the inner (outer) bearing race and the journal (bore); broken bearing balls or burn marks. 3) Other causes of noise: such as insufficient oil in the transmission, excessively thin or thick lubricating oil, or deteriorated quality; foreign objects falling into the transmission; loose fastening bolts; noise from the odometer flexible shaft or odometer gear, etc. Troubleshooting: ① A metallic dry friction sound from the transmission indicates insufficient oil or poor oil quality. ① Add oil and check the oil quality, replacing it if necessary. ② If a noticeable noise occurs when shifting into a certain gear while driving, it indicates wear on the gear teeth of that gear; if the noise is periodic, it indicates damage to individual teeth. ③ If the noise occurs in neutral and disappears after depressing the clutch pedal, it is generally due to the front or rear bearings of the first shaft or the constantly meshing gears; if the noise occurs in any gear, it is often due to the rear bearing of the second shaft. ④ A sudden impact sound during transmission operation is often due to broken gear teeth; the transmission cover should be removed immediately for inspection to prevent damage to components. ⑤ If the gears only make noise when shifting into a certain gear while driving, assuming the above conditions are intact, check if the meshing gears are improperly matched; if necessary, a new pair of gears should be reassembled. Additionally, it could be due to worn or damaged synchronizer gears, which should be repaired or replaced as needed. ⑥ If the gears collide during shifting, it could be due to the clutch not disengaging, incorrect clutch pedal travel, a damaged synchronizer, excessive idle speed, improper gear lever adjustment, or a tight guide bushing. In this situation, first check if the clutch can disengage, then adjust the idle speed or gear lever position respectively, and check the tightness of the fit between the guide bushing and the release bearing.
II. Transmission oil leak
If gear lubricating oil appears around the transmission and the oil level in the transmission gearbox decreases, it can be determined that there is a lubricating oil leak. Causes and troubleshooting methods: ① Improper lubricating oil selection, excessive foaming, or too much lubricating oil requires replacement or adjustment of the lubricating oil. ② Loose side cover, damaged gasket, or damaged oil seal; these should be replaced. ③ Loose drain plug and bolts securing the transmission housing and cover; tighten to the specified torque. ④ Leakage caused by a cracked transmission housing or worn oil seal in the extension housing must be replaced. ⑤ Loose or damaged odometer gear limiter must be tightened or replaced; leaking shift lever oil seal requires replacement.
When the one-way clutch fails, the torque converter loses its torque amplification function, resulting in the following malfunctions: the vehicle is weak when accelerating and starting, and the vehicle will not move without pressing the accelerator pedal, but once the vehicle is moving, gear shifting is normal and the engine power is normal. If a stall test is performed, it will be found that the stall speed is 400-800 rpm lower than the normal value.
Common lock-up clutch malfunctions include non-locking and constant lock-up. Non-locking manifests as high fuel consumption and engine running at high speeds but insufficient vehicle speed. Specific inspections should include checking the electrical circuitry, valve body, and the lock-up clutch itself. Constant lock-up manifests as normal engine idling, but the engine stalls when the gear selector is in power gear (R, D, 2, L). Checking the lock-up clutch requires disengaging the torque converter, which can only be performed by a professional automatic transmission repair shop.
3. Other Inspection Items 1. Inspect the exterior of the torque converter; visually inspect the exterior of the torque converter for damage and cracks, and check for wear and damage to the outer diameter of the oil pump drive hub. If any abnormalities are found, the torque converter should be replaced. 2. Cleaning the torque converter: When the automatic transmission has experienced overheating or the ATF oil is contaminated, the torque converter should be cleaned. Cleaning can be done using a dedicated flushing machine or manually. The method is to add clean ATF oil, vigorously shake and vibrate the torque converter, then drain the oil. Repeat this operation until the drained oil is clean. 3. Checking for internal interference in the torque converter: Internal interference in the torque converter mainly involves interference between the guide wheel and turbine, and between the guide wheel and pump wheel. If there is interference, the torque converter will make noise during operation. The interference check between the guide wheel and turbine is shown in Figure 1-110. Place the torque converter with the flywheel connection side down on the test bench, then install the oil pump assembly, ensuring the torque converter's oil pump drive hub is properly engaged with the oil pump's active part. Insert the transmission input shaft (turbine shaft) into the turbine hub, keeping the oil pump and torque converter stationary. Then, repeatedly rotate the turbine shaft clockwise and counterclockwise. If the rotation is not smooth or there is noise, replace the torque converter. The interference check between the guide wheel and the pump impeller is shown in Figure 1-111. Place the oil pump on the test bench and install the torque converter on it. Rotate the torque converter until the torque converter's oil pump drive hub is properly engaged with the oil pump's active part. Then, fix the oil pump and rotate the torque converter counterclockwise. If the rotation is not smooth or there is noise, replace the torque converter.
