Ultimate Guide to Car Transmissions

Guide to Car Transmissions

Arthur C. Clarke once said, “Any sufficiently advanced technology is indistinguishable from magic.”

It’s easy to think that our car’s engines run on magic. You put gas in, push the pedal, and the car moves. You press the brake, and the car stops. But the reality is that an engine is made up of hundreds of individual parts that contribute to making the car actually work.

One of those crucial parts is the transmission. In this guide, we’re covering everything you need to know about your transmission, including gas mileage and maintenance procedures.

What is a Transmission?

The transmission is another name for your car’s gearbox, and it can be quite complex to understand if you’re not a trained mechanic. Simply put, it works by turning the engine’s power into something that your car can use; it takes this power and transfers it to the wheels. Without a transmission, your car would not go anywhere.

You often hear about the differences between manual and automatic transmissions.

This refers to the method of shifting gears, which is the primary concern of drivers; automatic transmissions shift between gears without needing the driver to do anything, while manual transmissions require the driver to shift gears using a clutch and gear shift. This article will also cover continuously variable transmissions (CVTs), which are increasing in popularity among manufacturers.

The transmission functions the same as it refers to controlling the car’s speed regardless of if it’s automatic or manual. It does this through varying gear ratios.

Gear Ratios

To understand how gear ratios impact the car’s speed, we have to look at them in layman’s terms.

Imagine you have a gear generating the power (input) with ten teeth, which is connected to a gear that is receiving the power (output) with 20 teeth.

To turn the larger gear with 20 teeth, the smaller gear has to rotate twice because it’s half as big as the gear with 20 teeth. While the 10-tooth gear is turning quickly, the 20-tooth gear is turning slowly. Even though the 20-tooth gear is turning slowly, it delivers more power because of its larger size.

The ratio in this gear arrangement is 1:2, which is a low gear ratio.

When the driver engages a lower gear (such as 1st or 2nd), the gear ratio is high, which means the car will go slower because the gear that is on the output shaft is rotating slower than the input shaft.

As the driver shifts into higher gears, the gear ratio gets lower, increasing the gear’s speed on the output shaft and making the wheels rotate faster.


We use the terminology of torque at specific points in this guide. Here is a simple, quick definition to help get you on board.

Torque multiplied by its rotational speed of the axis determines the maximum power output of a car’s engine.

Manual Transmissions

As of 2016, only 18% of Americans knew how to drive a manual car.

Manual transmissions have been around since the early 1900s and have been continuously on the path to improvement since. If you learned how to drive before the ‘80s, chances are you learned on a stick-shift vehicle or know someone that had one. Nowadays, automatic transmissions dominate the American vehicle market, but that doesn’t mean manual transmissions have gone out of style.

The driver of a car with a standard transmission is required to use a gear stick and clutch to change the gear ratio, which then determines the number of times that the wheels rotate, which is also impacted by the amount of pressure you place on the accelerator.

The Clutch

When you get into the driver’s seat of a vehicle with a manual transmission, you’ll notice a pedal to the left of the brake and the accelerator; this pedal actuates the clutch.

By actuating the clutch, you’re disengaging the input shaft from the flywheel, which allows you to change gears; the transmission is being temporarily separated from the engine. Trying to shift gears without using the clutch can cause considerable damage to your transmission.

Here is a short, one-minute informational video that shows you how a clutch works if you’d like additional clarification:

Automatic Transmissions

Automatic transmissions didn’t show up in cars until 1948 by Oldsmobile. Ever since then, automatic transmissions have been pushing manuals out of the market.

A car’s driver with an automatic transmission is only required to shift gears between drive, park, neutral, etc. The transmission changes gear ratios independently through the torque converter; the amount of torque passed through the converter is dependent on how much pressure you apply to the accelerator (or gas pedal).

The Torque Converter

The torque converter is the equivalent of the clutch in an automatic transmission.

A torque converter is a type of fluid coupling. When a vehicle with an automatic transmission is idling, like in a drive-thru, the engine is turning slowly. This means that the amount of torque passing through the torque converter is limited, so it only requires light pressure to be applied to the brake to stop the car from moving.

If you stepped on the gas pedal while the car is idling, then you would have to apply more pressure to the brake to keep the car from moving. This is because the engine is spinning faster and pumping more fluid into the torque converter, causing more power to be transferred to the wheels.

Continuously Variable Transmission (CVT)

Continuously variable transmissions (CVTs) are becoming increasingly common in fuel-efficient vehicles because of the benefits they offer.

Often, the average driver won’t realize they’re driving a car with a CVT instead of an automatic transmission because they both do not require the driver to manually shift gears. A CVT can produce a smoother ride than other transmissions.

Remember how we talked about the importance of gear ratios?

CVTs don’t use gears. Instead, they use a system of belts and pulleys to produce an immensely wide range of gear ratios. The car’s internal computer decides how to adjust the pulleys to create the optimal ratio for the current driving situation.

Gas Mileage and Economy

A study by Edmunds discovered that, as of 2019, more than 80% of cars sold in Europe had manual transmissions, while only 3.9% of cars sold in the United States had manual transmissions.

The reason? Petrol prices in Europe are over double the price of gasoline here in the United States.

In the past, manual transmissions were a popular choice for people who wanted to save extra money on gasoline. This was because vehicles with automatic transmissions weren’t as efficient in transmitting the engine power to the wheels as manual transmissions were. Having a manual transmission meant that you had complete control over the shifting, and there was no middle-man.

Nowadays, technologies have been improving exponentially in automatic transmissions. Along with the introduction of CVTs, manual transmissions are getting a run for their money.

Of course, this only applies to newer cars. If you’re browsing older used cars and comparing them with automatic transmissions from the same time range, chances are they’ll get a better gas mileage than the other choices. If you’re shopping for newer cars, many of the popular fuel-efficient models are equipped with an automatic transmission or CVT.

Performing Maintenance

Even though the transmission is arguably one of the most essential pieces of a car’s engine, many car owners aren’t educated on proper transmission maintenance.

Transmission repairs and replacements can cost anywhere from hundreds to thousands of dollars, so it’s important to follow healthy driving habits and perform maintenance as needed.

Manual Transmission Maintenance

Maintaining proper driving habits is part of maintaining your manual transmission’s health.

It’s imperative that when changing gears, you’re pushing the pedal to the clutch down as far as it can go. Not completely engaging the clutch or bypassing it entirely increases the risk of future shifting problems. If you’re not engaging the clutch properly, you’ll hear grinding noises when you shift gears.

Also, a common myth is that you should downshift when slowing down. Older cars’ brake systems couldn’t handle stopping the high amount of power over a long period, but today’s’ brake systems are more than equipped to handle it. If you’re in the habit of downshifting when slowing down, it isn’t a terrible thing to do, but avoiding it could extend the life of your transmission.

Typically, you can expect to install a new clutch every 100,000 miles, but this amount can be shortened if you aren’t kind to your transmission. If you don’t replace your clutch when necessary, expect to be paying a chunk of money for a full transmission replacement.

Transmission Fluid

CVT, manual, and automatic transmissions all use transmission fluid that needs to be monitored and capped off as required.

As opposed to engine oil, which is primarily a lubricant, transmission fluid serves as a lubricant and hydraulic fluid. It lubricates moving parts, facilitates gear shifts, and cools the transmission.

Most mechanics argue that transmission fluid should be changed every 50,000 miles, while most automatic transmissions don’t need to be changed until 100,000 miles pass, or 150,000 miles in certain Ford transmissions. With this conflicting mix of numbers, the best thing to do is consult the service intervals listed in the user’s manual for your car.

Manual transmissions have fluid but are different from other transmissions. Anything that moves in a car’s engine has fluid or oil because it’s the easiest way to maintain moving parts. Rather than automatic transmission fluid, manual transmissions require more conventional oil. They also tend to be on a different maintenance schedule.

Certain driving habits can cause transmission fluid to deteriorate faster, just like oil or other vital automotive fluids. Hauling heavy loads and trailers, constant stop-and-go driving, or any other stressful use raises the transmission’s operating temperature. This heat then puts more strain on the fluid and transmission.

How to Check Transmission Fluid

Some manufacturers have begun to produce cars without a dipstick for transmission fluid because they recommend having it checked by a mechanic or service center instead. If you’re unsure if your car has an easily accessible dipstick, consult your owner’s manual.

To check your transmission fluid, you should follow the following steps:

  1. Consult your owner’s manual to determine the recommended procedure for checking the transmission fluid. Determine if the transmission fluid needs to be at operating temperature.
  2. Make sure your car is parked on a level surface to ensure an accurate reading.
  3. Some cars will require you to move the gear shift or selector into each gear before checking the fluid. Make sure your car is parked before exiting the vehicle.
  4. Pop the hood of the car and locate the transmission dipstick. This is usually a brightly colored tab or can be identified through the user manual.
  5. Remove the dipstick carefully so that you don’t get any fluid on hot engine parts. Wipe off the dipstick using a cloth or rag.
  6. Reinsert the dipstick.
  7. Remove the dipstick and read the fluid levels. The reading should fall somewhere between low and full.
  8. Reinstall the dipstick when finished and close the hood.

When to Change Transmission Fluid

So you checked your transmission fluid, now what? If the reading came back around full and you’re nowhere near the recommended mileage for changing, then you should be all set. If you’re still worried something is wrong, then take your car to a professional for a second opinion.

Like we mentioned before, the easiest way to find out when you should change your transmission fluid is by tracking the number of miles it’s been since your last change or by keeping track of the odometer if it’s a new car, but other circumstances may prompt you to change your transmission fluid sooner.

Another indication that you need to change your transmission fluid is particles or debris are in the liquid. The debris in the fluid can clog up the transmission filter and harm your engine’s performance.

Lastly, your car may be well over 100,000 miles since your last transmission fluid change. Does that mean you have to get it changed immediately?

If you haven’t noticed any deterioration or issues during shifting and everyday use, then adhere to the age-old saying, “If it isn’t broken, then don’t fix it.” Of course, it doesn’t hurt to consult a professional if you’re unsure that it’s time for a change.

Changing the Transmission Fluid

If you don’t have a car jack and other necessary tools lying around, then you should not attempt to change your car’s transmission fluid yourself.

The best route is to go directly to the service center of a dealership that services your make of car. This is because every car has different needs when it comes to the method of changing the transmission fluid and the type of transmission fluid that’s used. The mechanics at a dealership will already be experienced in servicing your specific vehicle.

Some repair centers will urge you to pay for a transmission flush, where instead of allowing the transmission fluid to drain manually into a pan, a flush system is used to force the old fluid out and pump in new fluid. A handful of manufacturers, like Honda, strongly recommend not doing the flush method. Consult your owner’s manual to figure out the best approach and type of fluid that should be used in your car’s engine.

If you’ve decided to change your transmission fluid yourself, then you’ll need a car jack, draining pan, transmission filter, and new transmission fluid. Follow these steps:

  1. Using the manufacturer’s recommended lift points, use a car floor jack to raise the vehicle from the ground.
  2. Place a container or drip pan underneath the transmission oil pan.
  3. Loosen the pan bolts. As soon as these are loosened, there will be a burst of transmission fluid. You must make sure the transmission is at normal operating temperatures before this is done, or you risk severe burns.
  4. Replace the transmission pan gasket and filter.
  5. Tighten the transmission pan bolts after draining is complete, and you’ve replaced the gasket, sealed the gasket if necessary, and replaced the filter.
  6. Use a funnel to replenish the transmission fluid.
  7. Reinstall the dipstick.

The Bottom Line

There it is! Everything you need to know about car transmissions.

To recap, every transmission functions the same way, but the differentiation comes from how much work the driver must do to change gears. The different transmissions are automatic, manual, and continuously variable.

Although manual transmissions are dwindling in the United States, they’re still found in many high-end sports cars and antique cars. Drivers like manual transmissions because they allow more control over the driving experience, and, as a bonus, more gears means better gas mileage.

Regardless of the type of transmission you have, proper driving habits and scheduled maintenance are required to keep your car in good health. Avoid putting too much stress on your vehicle, or if you’re continually doing heavy pulling, make sure you’re monitoring your transmission fluid because you may need to change it earlier than the schedule indicates.

Brett Gordon

The engine behind editing at DigMyRide and the brains behind its build. During the day, Brett is a thirty-something dude from SoCal climbing the corporate ladder, but by night, he spends his time contributing to the online world of automotive tech & trends.