Sergeant Clutch Certified Engine & Transmission Shop

6557 Walzem Road San Antonio, Texas 78239 Call 210-239-1600
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DIY Car Maintenance Tips
The 4 Most Common Alternator Problems
All About Automatic Transmission
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All About Automatic Transmission

If you are car shopping today, it is hard to come across manual vehicles. Many large auto manufacturers are even ending production of manual transmissions. Most people love driving automatics because they are hands-free. You don’t have to worry about the clutch or switching gears because the car does all that hard work for you. However, automatic transmissions are the most complicated mechanical component in today’s vehicles.

What is a transmission?

Transmissions are connected to the back of the engine and transfer the power from the engine to the wheels. The transmission’s role is to make sure enough power is being delivered to the wheels while keeping the engine within a certain Revolutions Per Minute (RPM). It is able to achieve this by switching gears.

What is an automatic transmission?

Automatic transmissions are made up of a number of moving parts. Automatic transmissions consist of mechanical systems, hydraulic systems, electrical systems, and computer controls. Each of these components works together in perfect harmony – until there is a problem.

Automatic transmissions are primarily made up of the following:

·         Planetary gear sets

·         Hydraulic system (includes oil pump, valve body, clutches, and bands)

·         Seals and gaskets

·         Torque converter

·         Governor, modulator, and throttle cable

·         Computer (in newer vehicles)

Planetary Gear Sets

Planetary gear sets provide forward and reverse gear ratios. The system consists of a sun gear, a ring gear, and two or more planetary gears. These are all connected to each other and spin on shafts. Many combinations are possible. In fact, using two or more planetary sets provides different forward and reverse speeds. If you’ve ever heard of a five, six, or seven-speed automatic, it is referring to the planetary gear sets.

Hydraulic System

The hydraulic system is made of passages and tubes and sends transmission fluid under pressure to all parts of the transmission and torque converter. The transmission fluid helps the car in many ways, including shift control, general lubrication, and transmission cooling. The oil pump sends the transmission fluid through the valve body to control the clutches and bands, which control the planetary gear sets. The transmission must operate at a normal temperature, so part of the fluid is sent through a steel tube to a special chamber, which is submerged in anti-freeze in the radiator. The fluid cools down as it passes through. Most of the transmission’s parts are submerged in fluid consistently. The fluid helps each part operate properly.

Seals and Gaskets

Seals and gaskets control the hydraulic fluid’s flow and prevent it from leaking. The main external seals are the front seal and rear seal. The front seal holds together the point where the torque converter mounts to the transmission case so the fluid moves freely. The rear seal prevents the fluid from leaking past the output shaft.

Seals are typically made from rubber, while gaskets can be made from paper, cork, rubber, silicone, or soft metal. A seal is meant to keep the oil from leaking past a moving part. A gasket, on the other hand, is a kind of seal that seals together two stationary parts.

Torque Converter

On a standard vehicle, you may be familiar with the clutch. On automatic transmissions, the clutch is known as the torque converter. This allows the engine to continue to run – even when the car is stopped.

Governor, Vacuum Modulator, and Throttle Cable

These three parts are essential to non-computerized transmissions because they tell the transmission when to shift. The governor connects to the output shaft and regulates hydraulic pressure depending on the vehicle’s speed. The next types of devices monitor the engine load. The throttle cable monitors the position of the gas, while the vacuum modulator monitors the engine vacuum.


Newer vehicles may be equipped with computers. The computer has many sensors on the engine and transmission, which can detect various parts of the car, including throttle position, vehicle speed, engine speed, engine load, brake pedal position, and more. The computer will send signals to a solenoid pack inside the transmission when it receives the results. These computers even learn your driving habits and will adapt to your style to time shifting precisely according to your needs.

An extra perk is that these computers can self-diagnose the vehicle. This means they can detect a problem before the problem has even occurred and warn the driver by lighting the correct indicator on the dash. Then, all you need to do is have a technician read the trouble codes that can pinpoint the problem.

Sergeant Clutch Discount Transmission and Auto Repair Shop

If you believe you are having transmission troubles, bring your car in at Sergeant Clutch for a free transmission diagnostic performance check. We perform a number of transmission repair services. At Sergeant Clutch, the customer is our priority – which is why we offer various offers and coupons. Call us at 210-239-1600 for more information.