What are the causes of idle noise in Honda 5AT transmission?

[JoyLee]

The cause of idle noise in Honda 5AT transmission may be bearing damage. Reasons for transmission idle noise: Excessive deviation in the perpendicularity between the front face of the transmission housing and the concentric line of the first and second shafts, or excessive coaxiality deviation between the first/second shafts and the crankshaft. Damage to the front ball bearing of the first shaft. Damage to the rear ball bearing of the first shaft. Damage to the front bearing of the second shaft. Mismatched constant mesh gear pair. Constant mesh gears worn into a stepped shape or with damaged teeth. Changes in gear meshing conditions due to replacement of shafts or bearings. Diagnostic methods for transmission noise: With the engine idling and the transmission in neutral, if noise occurs and intensifies when the handbrake is engaged but disappears when the clutch pedal is depressed, and the noise is not noticeable during vehicle operation, it indicates wear and looseness in the rear ball bearing of the first shaft or its housing. If the transmission produces uneven noise that becomes louder when the handbrake is engaged and remains audible during driving, it often indicates poor meshing of the constant mesh gears. Excessive deviation in the parallelism of the transmission's three shafts or between the first/second shafts and the crankshaft can cause such noise, which intensifies when driving in non-direct gears. If the transmission exhibits obvious noise during engine idle that increases with RPM and turns into gear impact sounds, gently push/pull the gearshift lever. If noticeable vibration is felt, slightly loosen the transmission cover bolts and adjust its position. If noise disappears or reduces at certain positions, it indicates original misalignment of the transmission cover. If noise persists, inspect whether the shift fork fastening screws are loose or the fork is deformed, and further check for gear damage. When noise increases uniformly with engine RPM, it's often caused by changed gear meshing conditions after intermediate shaft bearing replacement.