Causes of a Slipping Transmission

by Jason Medina

A common vehicle mechanical problem is a slipping, or improperly engaging, automatic transmission. A slipping transmission occurs when a transmission's gear sets fail to engage or synchronize properly. This significantly reduces the ability to drive the vehicle and can lead to premature automatic transmission failure if not corrected promptly.

Low Automatic Transmission Fluid Level

One of the most common causes of a slipping transmission is a low automatic transmission fluid level. Automatic transmission fluid is responsible for providing the hydraulic, or fluid, force necessary to power the inner workings of an automatic transmission. A low transmission fluid level reduces the hydraulic pressure necessary to properly shift and operate the automatic transmission gear sets, which can routinely cause the transmission gears to slip out of place or shift erratically.

Dirty Transmission Filter

A dirty and/or clogged automatic transmission filter can impede the normal flow of automatic transmission fluid throughout an automatic transmission and cause the transmission to slip. Adequate, unobstructed transmission fluid flow is necessary for the optimal operation and function of an automatic transmission, including the function of the transmission bands and gears, two transmission components that routinely cause transmission slippage.

Worn Transmission Bands

An automatic transmission uses a series of small, rubberized transmission bands to synchronize transmission gear operation. These rubber bands are designed to wrap around each individual transmission gear and synchronize the movements between each gear set. The automatic transmission fluid provides the fluid force to shift the gears; the transmission bands anchor each gear set together and allow the shifting gears to work in unison. Worn or damaged transmission bands can allow slack to develop around the transmission gears, a condition that can cause the transmission gears to slip out of place.

Faulty Torque Converter Action

An automatic transmission uses a special pump called a torque converter to pump and pressurize automatic transmission fluid throughout the entire automatic transmission system. A torque converter is necessary to sufficiently pressurize transmission fluid to provide the pushing action required to shift the transmission gears and to maintain transmission operation. A faulty or defective torque converter seriously impedes automatic transmission fluid pressurization and can cause a transmission to slip by allowing transmission gears to slip out of place or operate erratically.

Maladjusted Transmission Bands

For an automatic transmission to shift properly and function within normal limits, its transmission bands must be adjusted to factory-specific guidelines. Transmission bands that are too tight can cause premature transmission gear wear and lead to band breakage; transmission bands that are too loose can cause transmission gear slippage and a freewheeling situation where a transmission gear fails to engage properly. Loose transmission bands reduce the operational power of an automatic transmission and, in addition to causing a slipping transmission, can cause a vehicle's engine to work harder to make up for the faulty transmission function.

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