Here’s Why Your Transmission is Slipping

It’s become one of the biggest transmission recalls ever, but software is just one of many things that could cause a transmission to slip. Valves, fluids, gears, clutches, and gears are all susceptible to issues that could cause the mechanism to falter. The transmission is one of the most complex components of an automobile, and if it's not operating correctly, you'll certainly feel it. 

Despite the complexities, maintaining your transmission is a simple and effective way to prevent these issues from happening and keep your vehicle running smoothly for longer. A properly maintained transmission is a happy transmission, as the saying goes. Learn how and why your fluid affects the rest of the transmission, as The Drive’s manic informational team explains the reasons your transmission is slipping.

As part of a vehicle’s drivetrain, a transmission is a device that takes power from the engine and delivers it to the wheels to move the vehicle. It helps match the speed of the engine to the speed of the car through the various gears, and lets the car travel in both forward and reverse depending on the gear selected. The most common types of transmissions in average consumer vehicles are manual transmissions, traditional automatic transmissions, and continuously variable transmissions (CVT). 

A manual transmission is one that requires a clutch pedal and gears actuated by the driver using a gear shifter, while an automatic transmission does not require a clutch pedal and runs through its gear sets on its own. A CVT is a different type of automatic transmission that uses belts or chains paired with pulleys to create smooth acceleration without stepping through discrete gears. 

When we talk about a slipping transmission though, we're usually talking about an automatic transmission. In simple terms, the main components of an automatic transmission are the torque converter, the valve body, and the planetary gear sets. The torque converter is the device that transfers and multiplies energy from the engine, the valve body controls gear and fluid timing, and the gears determine the drive ratios. Different gear ratios make for different acceleration, speed, and driving characteristics.

A slipping transmission is a symptom of a bigger problem. Let’s figure out what’s going on and, hopefully, assuage your fears.

Like an engine without motor oil, a transmission without transmission oil will fail. The transmission also might act up if the fluid levels are too low or too high. In the case of slipping, the transmission fluid is likely low or has been contaminated. Without enough fluid, the transmission's internal hydraulic components can't generate enough pressure to fully engage the clutches and bands inside. This can cause slip which quickly wears out the transmission. Similarly, old and dirty transmission fluid, or a clogged transmission filter, can cause problems. A transmission fluid and filter change, or in extreme cases, a flush, can often solve a lot of problems.

Transmission bands and clutch packs are internal mechanisms that are used to engage or brake the gears. Wear over time can eat at these components and make them less effective. If they lose their friction material, they may grip ineffectively, and your transmission might slip.

A transmission solenoid controls fluid distribution. If it’s faltering, transmission components won't get the proper fluid pressure they need to engage. This can cause slip as failing solenoids can cause clutches and bands to not engage properly.

A torque converter is the primary connector between the engine and the transmission. If it fails or is not operating correctly, the transmission can exhibit signs of slipping.

Think about how gears work. Sets of teeth grip each other and push each other along. If those teeth are worn down due to low or contaminated transmission fluid, age, and general wear, they won’t mesh properly or transfer power. This could also lead to slippage. It's rare for gears in an automatic to wear before the bands and clutch packs, but if they do, you're in for an expensive rebuild or replacement.

Computers might be smart, but without artificial intelligence, they’re still limited to what humans program into them. If there’s an error in programming or in signals from the vehicle's various sensors, it could lead to or cause transmission slipping or stalling. Ford’s PowerShift transmission is a perfect example of this issue.

You might expect that the first step in fixing a slipping transmission is changing or flushing the fluid, but that’s not always the case. A fluid and filter refresh can help in some cases, but not always—read on.

If the transmission is slipping, it likely means it already has worn internal components. In some cases, friction material from parts like the clutch packs might be worn off and floating around in your used fluid. Although that’s bad, the friction material floating around might still be adding just enough friction to keep the transmission going. If that fluid is replaced, the result might be even worse slipping. 

Additionally, adding new fluid where soiled fluid resided might move particles and contaminants around and further damage the transmission. 

At this point, you could try using a product such as Lucas Transmission Fix Stops Slip, but that rarely works. If your fluid is bad, that’s typically an indication of a larger issue that requires a professional diagnosis. Transmissions can be repaired and rebuilt, but because they are so complicated, fixes are typically left to the professionals. Unfortunately, transmission repairs can cost thousands of dollars. 

The best way to prevent bad fluid is to perform changes and/or flushes roughly every 40,000 miles, or at intervals specified by the manufacturer, while the transmission fluid is still in good condition. While some automakers claim their cars use "lifetime" transmission fluid, this is rarely the case in reality. Transmission shops will often advise that these vehicles can benefit from a fluid change at regular intervals just the same.

Yes, your fluid might be the issue, whether it’s contaminated, too high, or too low. However, a full flush is typically done with a professional machine at a shop that changes out every last drop of fluid, so it’s not an easy home garage job.

Depending on your vehicle, how you maintain your transmission will vary. Some systems are completely closed from the factory and require professional service. Likewise, a full transmission flush requires a specific machine only found at service centers. However, if you’re just looking to service the transmission fluid and change it out, and your manufacturer hasn't locked you out, that’s a job for your home garage. Learn more from The Drive’s guide to transmission fluid.