What Causes Abnormal Noise in the Transmission When Exceeding 40 mph?
2 Answers
Transmission abnormal noise when exceeding 40 mph is caused by bearing wear, low part precision, poor lubrication, etc. Specific reasons are as follows: Bearing wear: When bearings wear out, their clearance increases, leading to reduced fitting precision. Damaged bearings cannot operate normally, resulting in abnormal noise and even damage to transmission components, which may escalate the fault. Low part precision: Another reason is abnormal noise caused by low-precision parts selected during the wear or replacement of transmission components, such as excessive clearance between worn or newly replaced gears and the original gears. Poor lubrication: Insufficient or overly viscous lubricant leads to poor lubrication and abnormal noise. The corresponding lubricant should be replaced; otherwise, it will accelerate transmission wear and shorten its service life.
My previous car had abnormal noises from the transmission when the speed exceeded 40 km/h, which is quite common and usually caused by gear wear. Prolonged driving on uneven roads can make the gears rattle, especially noticeable during acceleration. Insufficient lubrication is another factor—low or dirty oil can increase friction noise. Additionally, damaged bearings can amplify the sound, making it as harsh as metal grinding. I recommend checking the oil level first. If it's abnormal, timely oil replacement can help. It's best not to ignore it—have a professional mechanic diagnose it with a stethoscope to avoid major repairs later. Otherwise, it might affect the clutch, making driving unsafe and costly, with repairs costing hundreds or even thousands. An oil change is inexpensive, just a few dozen dollars, but regular maintenance is essential—inspect every 20,000 km. Ignoring the noise could lead to complete transmission failure, and replacing the entire assembly would cost tens of thousands, which is a huge loss.
