Short of a car’s powerplant, the most critical component in a vehicle is the transmission. That means, should some malfunction occur, the driver is likely to end up on the side of the road like a beached whale at sunset.
While not every weird noise or smell immediately spells disaster, they could be symptoms of transmission failure. Learn what transmission trouble looks (and feels) like, what may be wrong, and what you can do.
What Is An Automatic Transmission?
Unlike manual transmissions that change individual gears by means of a hand-activated lever on either the steering column or on a center console, automatic systems change gears by means of electro-mechanical switches, solenoids and speed sensors. These are typically supported by a torque converter, plus a hydraulic pump, and are all lubricated by an ATF (Automatic Transmission Fluid) liquid.
Once an engine reaches a pre-determined RPM, the transmission complex automatically selects an optimal gear ratio for engine efficiency. Then, while the car’s engine continues to produce proper power and torque, the system establishes and maintains the car’s desired speed.
Put more simply: the transmission is what transmits power from the engine to the wheels. It also keeps that power manageable, so the tires don’t burn off your car. Without one in good working order, you’re not going anywhere.
The transmission complex consists of several core elements, but some of the most important include:
- Torque converter – This donut-shaped device uses fluid to transmit engine-generated power to the transmission system. The torque converter is what allows your car to come to a complete stop without the engine stalling.
- Transmission pump – Driven by the spinning motion of the torque converter when the engine is running, this pump pressurizes and moves fluid throughout the automatic transmission.
- Planetary gearset – These live at the heart of your transmission and consist of a central drive gear (the Sun Gear) orbited by a few “planet” gears, all of which is surrounded by a ring gear. Thanks to the planetary gearset’s design, the gear ratios in an automatic transmission can increase and decrease automatically.
- (Gear ratio represents the relationship of rotational speed between two interlocking gears – in this case, the input and output shafts – which determines how much torque is applied to the wheels.)
- Clutches and Bands - All involved gears are activated by a number of hydraulic clutches activated by steel bands that physically move necessary clutches/gears in and out of position. These activations result in various gear ratio deliveries that produce differences in resultant power and torque, that is then delivered to the car’s differential (rear-end) and on to its driving wheels.
Symptoms of Transmission Failure
Typically, there are a number of symptoms that announce the onset of an automatic transmission failure.
Irregular or Slipping Gears
The most common symptom relating to a transmission problem involves an inability or difficulty to change gears. This can sometimes be felt as a hesitation or slipping/dragging sensation during shifting.
Gear change issues could be caused by low ATF levels, or even a weak transmission pump. Bear in mind that clutch and gear change activation is largely driven by hydraulics, so if the fluid level is low or not pumping properly, the entire system is likely to behave irregularly.
If levels are low, this usually means there is a leak somewhere – perhaps a crack or puncture in the transmission pan, a gasket failure, or a crack in the fluid line or axle seal. Problems within the torque converter itself could affect fluid levels too.
Additionally, many modern vehicles rely on computers for just about everything – including telling the transmission which gear to go into. A damaged ECU could cause shifting issues. Alternately, an engine problem could be causing the computer to prevent shifting into certain gears.
Unusual Sounds
If you hear excessive whining, grinding, high-pitched sounds, and/or sudden metal-on-metal noises, it’s likely related to some kind of transmission trouble.
Individual gearsets carry the load when moving from one shifted ratio to another. If one or more gears in the planetary gearset are worn, odd sounds can be created even when the transmission is in neutral. Similarly, stressed metal bands move gears from one position to another and clutches assist in moving from an in-gear position to neutral. If one of these fails, you might hear unusual sounds.
A faulty transmission pump will also often announce itself. You may hear a whining noise than gets louder as you accelerate.
Odd Smells During Operation
Generally speaking, weird car odors are never a good sign but burning smells are particularly worrisome. If the smell is a result of transmission trouble, it will likely be caused by old or leaking transmission fluid. These smells are sometimes accompanied by excessive heat emitting from the transmission hump within a car’s interior.
Obvious Fluid Leaks
This is a really simple announcement when it comes to transmission problems. If you find slightly red fluid on the floor of your garage or on your driveway, and it seems to be coming from your vehicle’s middle section, chances are you’ve got a leak somewhere along the transmission complex.
Anti-freeze, as well as some windshield wiper fluids, are also reddish in color. To ensure it is transmission fluid, check the consistency and smell. It should feel oily, similar to engine oil, and have a slightly sweet smell.
Keep in mind though, that older transmission fluid will sometimes have a thicker consistency, darker reddish-brown hue, and if it has broken down, a burnt smell.
Check Engine Light
A pretty good sign that something is up, your check engine light will usually throw up an alert if transmission trouble is brewing. Some vehicles have a dedicated transmission warning light that illuminates if the component is overheating. These can look like anything from a gear with an exclamation point, to a thermometer with waves.
Transmission Troubleshooting
Now that you have a fair idea of the types of general symptoms involved in a transmission malfunction, let’s go through some remedial actions.
Check ATF levels.
Since low levels are a common cause of many of the symptoms outlined above, checking the automatic transmission fluid is a good first step when attempting a diagnosis.
To check your ATF levels, you will need to locate the transmission dipstick, which lives in the engine compartment under the hood. To ensure it isn’t confused for the engine-oil dipstick, the transmission dipstick sometimes has a different color, or even a special symbol. If you have trouble finding it, check your owner’s manual for guidance.
Once you locate the correct dipstick, you’ll need to start the vehicle. Transmission fluid expands in the heat, so if you check it while it’s cold, you may incorrectly assume the level is low. Allow the engine to idle – and be sure to park on a level surface.
Take the dipstick out and wipe it down with a clean rag or paper towel. Then, reinsert it slowly and pull it back out. Check the fluid level against the fill marks notched into the dipstick.
If it’s too low, there’s a good chance you have a leak. If you’d rather be sure before heading to a service center, you can always top off the fluid and then check it daily to see if/when the level drops again.
Check ATF Condition
While you’re in there checking fluid levels, give that ATF a once-over. Does the color seem to be a healthy reddish-pink with an odorless or slightly sweet smell? Or is it dark and sludgy, smelling burnt and acrid?
If it’s the latter, a transmission fluid flush and change may solve the problem, but it’s best to get the vehicle checked out by a qualified mechanic to be safe. Where there’s smoke, there’s usually fire; and where there’s burnt transmission fluid, there’s likely overheating.
Pull the computer code.
If you suspect transmission problems based on an illuminated dashboard light, and would like to gather a little more information before visiting a mechanic, you can connect an OBD-II reader and pull the code yourself.
Code readers run the gamut on price, but decent models can be had for less than $50. If you’re a DIYer, it’s a worthwhile tool to keep on hand. You may not be able to complete the repair yourself, but it certainly saves diagnostic time (and money) when you take it in for service.
Take it to a service center.
Whether you’re disinterested in any kind of self-diagnosis, or transmission repair is a little beyond your skillset, taking your vehicle to a reputable mechanic or service center is always a good move. Low ATF levels or failing transmission components can create excessive friction and heat, causing major problems. A professional will not only provide you with a diagnosis, but also a viable course of action.