It's not good when you feel your car shake or hear it whine as it struggles to go into the next gear. If this is happening regularly, there are a couple of possible reasons why it is slipping gears when your car attempts to automatically shift. You should address the following problems before the transmission fails completely.
1. Transmission Fluid Is Low and/or Burnt
One possible reason why your car's automatic transmission keeps slipping could be an issue with the transmission fluid. The fluid's level may be low, burnt, or even both. To keep the gears and clutch within the transmission moving smoothly, they need to be properly lubricated at all times. If the fluid level is low, they will not be coated with enough lubricant, and the clutch and gears may stall momentarily, which causes the transmission to miss.
Another issue that could be affecting the fluid is that the extreme heat within the transmission has burned the lubricant. This can happen when the transmission is running too hot or when the level is too low. Depending on your car's make and model, you may be able to add or change your transmission fluid according to the owner's manual. Just know that if you put too much or too little fluid in, it could adversely affect the pressure within the part. If you are uncertain as to how to avoid this or if your car has a closed system, you should have a professional do the job for you.
2. Teeth on the Transmission Gears Are Worn Down
Another possible reason why the gears are slipping during shifting is that their teeth are worn down. This wearing down of the teeth can be caused by either natural wear or a misalignment of the gears. When the teeth are worn in sections, the gears will not be able to fully grab onto each other. When these areas try to come together during a shift change, it may take a moment for them to fully engage, causing the pause you are experiencing. In this case, the gears would need to be replaced.
No matter the reason, if your transmission keeps slipping while your car is trying to shift gears, you need to have it looked at as soon as possible to avoid having it fail completely while you are driving. Take your car to a shop that offers auto transmission services to have them diagnose the cause of your slipping transmission so that they can take the appropriate action to fix it.