Why Does My Automatic Transmission Act Funny?

CARS.COM — Why does your automatic transmission act funny? The most common causes include leaking seals, mechanical damage, worn-out transmission fluid or inadequate transmission fluid level, but we must examine what “acting funny” means when referring to one’s transmission before recommending a course of action. Do any of the following symptoms seem familiar to you?

Slipping

When an automatic transmission seems to slip in and out of gear, or the engine revs up but the vehicle goes much slower than the engine seems to be running, it’s known as slipping. Sometimes the gears reengage harshly.

Related: More Drivetrain and Transmission Advice

Shuddering

This is where the whole vehicle shudders and shakes while driving, as if it’s having a convulsion. It feels like you’re driving over rumble strips even if you’re on a smooth highway.

Neutral Drop-Out

A condition that feels similar to slipping, Neutral drop-out is where the transmission drops into Neutral when the vehicle comes to a stop or while driving, typically at slower speeds. Sometimes when driving, the transmission drops out of gear resulting in the engine racing up, and then either sliding — or banging — back into gear, or you step on the gas and the engine revs but the vehicle goes nowhere as if it’s in Neutral.

Heavy Transmission Vibration

This heavy vibration is felt throughout the vehicle under acceleration, especially when the transmission is under load, such as driving up a hill or pulling a trailer. Though many things can make a car vibrate, this type of transmission vibration will subside when coasting or idling.

What’s Causing This?

The potential causes behind these behaviors are many. The most common include leaking internal or external transmission seals; mechanical damage to the transmission and/or the transfer case’s vital internal hard parts such as gears, drums, etc.; old, worn-out transmission fluid; improper fluid; electrical software and hardware glitches; worn drivetrain components; bad transmission and engine mounts.

What Can You Do?

Most of the problems listed above require a mechanic, certainly, but you can start by inspecting the color, consistency and smell of the vehicle’s transmission fluid. Low transmission fluid level can cause the slipping described above.

Even if the vehicle is not experiencing any of the problems above, if the transmission fluid is brown or lightly dark, then it’s probably time for transmission service, essentially a transmission oil change. Like the engine, the transmission has a filter and oil (called fluid because it does more than lubricate) that needs to be changed at regular intervals outlined in your owner’s manual. If there’s no reference in your manual, then check with your mechanic.

If one or more of the symptoms described earlier are present and the fluid smells burned and feels rough or gritty between your fingers, then have a professional look at it, because more than simple service is required.

For the conditions above, we recommend transmission repair specialists who have access to diagnostic repair info that could lead directly to the cause of the problem, rather than muddling around in hit-and-miss fashion. They can run pressure tests, dye-leak tests and an electronic diagnostic scan of the drivetrain control module.

Diagnostic costs vary with the eventual verdict, but you can determine the likely cost of transmission fluid maintenance for your specific vehicle in your area using our fair-price estimator. After inputting your make, model and year, select the maintenance category and then the service called automatic transmission fluid/filter change.

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