Common Gearbox Faults
Modified on: Wed, 11 Jan, 2023 at 5:17 PM
- A badly worn oil seal will allow oil to be thrown along the first motion shaft onto the clutch. When a new seal is installed it is essential to ensure that it is wholly concentric with the shaft.
- Jumping out of gear may be nothing worse than broken or weak indent springs. This problem may also be due to weak synchromesh springs and seriously worn dog clutch teeth or from a worn or bent selector. Incorrectly placed selector balls can also cause jumping out of gear.
- On some models the tail shaft seal can be removed and a replacement installed without removal of the gearbox.
- On some BMC models a nylon cup is fitted. If it becomes worn or displaced sloppy gear changes will result.
- Wear in the gear selector forks or selector gate can result in difficult gear engagement and excessive movement in the shift lever. For the MGB, it is also possible that the setscrews and washers securing the shift lever to the gearbox have been replaced with non-standard items or worked loose.
- Low oil level may cause noise and premature wear.
- If chipped gear teeth are suspected, the oil should be drained into a clean reservoir and inspected for metal swarf. In the event of severe damage to the teeth, the gearbox should be overhauled.
- A disintegrated thrust washer will result in jumping out of gear or complete gear failure.
- If a gear change is accompanied by the grinding of gears or requires great difficulty it is likely due to severe wear in the baulk rings. To prevent premature wear do not rest your hand on the gear lever when driving or fail to blip the throttle when selecting a lower gear.
- In the event that balkiness occurs when engaging all the gears, it is more likely that the problem is a dragging clutch.
- If the gearbox emits noise when the car is stationary, engage the clutch and listen. If the noise persists with the clutch engaged, the problem lies in the engine or clutch.
- If the gearbox emits noise when the car is in motion, note the gear or gears in which it is most noticeable. Most noises will start as a whine or hum and then progress to a harsher note as the problem worsens.
- Bearing wear emits a light hissing noise that becomes a more pronounced knock as it starts to fail.
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