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Manual transmission noise often stems from issues with oil, gears, or the clutch—not always the gearbox itself. This article outlines 5 inspection points to help you diagnose root causes early, reducing unnecessary disassembly, time, and cost.

■ Gearbox Noise Is a Red Flag—Don’t Ignore It
In manual transmission systems, abnormal noises—such as whining, knocking, or grinding—signal internal issues. Ignoring these can lead to drivetrain or clutch damage.
By following a structured inspection process, you can identify the source without rushing to open the gearbox.

■ Gear Oil Condition & Level
Insufficient or degraded oil leads to poor lubrication and abnormal noise, especially during low RPM or shifts.
✅ What to Do:
・ Check oil level and top up as needed.
・ Replace old oil per OEM specs.
・ Use the correct viscosity grade.

■ Gears and Output Shafts
Worn or chipped gears can cause noise in specific gears or under heavy load.
✅ What to Do:
・ Listen during shifts—identify if it’s gear-specific.
・ If persistent, disassemble to inspect gear teeth and alignment.

■ Clutch System and Release Bearing
If noise appears while pressing or releasing the clutch, a worn release bearing or clutch disc is likely.
✅ What to Do:
・ Hold the clutch down—listen for whining or rumbling.
・ If present, inspect and replace the release bearing or clutch disc.

■ Gearbox and Engine Mounts
Loose or damaged mounts cause knocking or misalignment noises during shifts or acceleration.
✅ What to Do:
・ Check all rubber mounts for cracking or looseness.
・ Replace torn or weak parts to stabilize the system.

■ Worn Synchromesh
Grinding sounds during gear engagement—especially in 1st or reverse—point to worn synchromesh mechanisms.
✅ What to Do:
・ Test whether grinding occurs at every shift.
・ Open gearbox if consistent issues are found.

■ Reduce Noise with High-Precision Gear Components
Using high-quality parts reduces long-term noise and extends the system's life.

✅ Recommended: Siam Asahi Manufacturing (Thailand) Co., Ltd.
A trusted supplier of drivetrain components engineered for durability:
・ Precision CNC + forging ensures minimal tolerances.
・ Materials: Cast steel and aluminum alloys built for load-bearing.
・ Customization: Tailored parts for specific transmission systems.
・ ISO-certified: All products tested for strength and performance.

■ For more details, please download the PDF or contact us directly.

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