BMW 640i Gears slipping when accelerating Inspection at your home or office.

Common reasons for this to happen:

• Low Transmission Fluid: If you’re of driving age, you’ve heard this one time and again, but it bears repeating. The number one cause of all transmission problems, from slipping to abnormal sounds, is low transmission fluid. If the fluid is low, a number of problems can crop up that will make the transmission slip, including overheating.

• Fluid Is Burnt: Just as you need the right level of transmission fluid, you also need that fluid to be in good condition. Like engine oil, transmission fluid needs to be changed periodically, or it becomes burnt and the level of contaminants in the fluid can rise to dangerous levels.

• Transmission Fluid Leaks: This one relates directly to low fluid, but it’s the cause of the transmission fluid being low. Transmission leaks can range from miniscule to catastrophic, but they all affect the level of fluid in your transmission.

• Gear Wear: If you have a high-mileage vehicle with the original transmission, the gears may just be worn out. This applies even if you’ve taken care of the transmission with regular services. There are simply only so many miles the average transmission can operate. If your gears are worn, they won’t mesh together properly, creating slippage.

• Broken Transmission Bands: Transmission bands connect the various gears in your transmission to one another. Over time (and particularly if you don’t maintain the transmission or drive with low fluid), they wear. Once they become too worn, or they break, your transmission will slip.

• Failing Torque Converter: The torque converter is what transforms energy from the engine into something your transmission can use. They work with transmission fluid, so low fluid levels could cause damage here as well. Once the torque converter is damaged, your transmission will slip.