Beginner's Auto Maintenance & Repair

The Drive Train

Drive Train:

The drive train (drivetrain or powertrain) is a series of parts that transfer energy from the combustion engine to the wheels. The drive train has three main components: the transmission, drive line or drive shaft, and differential. In some four-wheel drive vehicles, a transfer case is also necessary.

 

Powertrain for a Subaru vehicle. The engine and transmission are seen on the right. The drive shaft is inthe middle and the differential is on the left at the center of the rear axle
Powertrain for a Subaru vehicle. The engine and transmission are seen on the right. The drive shaft is in the middle, and the differential is on the left at the center of the rear axle

 

The rotation of the crankshaft in the internal combustion engine does not equal the rotation of the wheels, thanks to using gears. The lower speeds are due to lower gears, while the higher rates are thanks to higher loads. Yet, the

RPM which is read on the dashboard tachometer may be relatively constant (or stay within a range) through all speeds. The transmission, which is where the actual gears are located, takes an input speed from the crankshaft and reduces it to the output speed until the vehicle is in direct drive. In other words, it changes the gear ratios. So, in first gear, you might have an input-to-output ratio of 4 to 1. t means that as the input shaft goes around four times, the output shaft goes around one time. At 4,000 RPMs input, you would have 1,000 RPMs output. The second gear may have a 3 to 1 ratio, and the third gear a 2 to 1 ratio. The fourth gear would be direct drive with a 1 to 1 ratio.

Think of the sprockets on a bicycle. A large one on the front that rotates as the bike is pedaled, and both a large and small sprocket on the back wheel with a chain that connects the front sprocket to the rear sprockets. As the gears are

changed, so is the mechanical advantage for the pedaling person. In direct drive, the input and output speeds are the same; there is no gear reduction. Modern vehicles have overdrive, which is a ratio of 0.75 to 1. Drive Train:

The drive train (drivetrain or powertrain) is a series of parts that transfer energy from the combustion engine to the wheels. The drive train has three main components: the transmission, drive line or drive shaft, and differential. In some four-wheel drive vehicles, a transfer case is also necessary.

Powertrain for a Subaru vehicle. The engine and transmission are seen on the right. The drive shaft is in the middle, and the differential is on the left at the center of the rear axle.

The rotation of the crankshaft in the internal combustion engine does not equal the rotation of the wheels, thanks to using gears. The lower speeds are due to lower gears, while the higher speeds are thanks to higher loads. Yet, the

RPM which is read on the dashboard tachometer may be relatively constant (or stay within a range) through all speeds. The transmission, where the actual gears are located, takes an input speed from the crankshaft and reduces it to the output speed until the vehicle is in direct drive. In other words, it changes the gear ratios. So, in first gear, you might have an input to output ratio of 4 to 1. It means that as the input shaft goes around four times, the output shaft goes around one time. At 4,000 RPMs input, you would have 1,000 RPMs output. The second gear may have a 3 to 1 ratio, and the third gear a 2 to 1 ratio. The fourth gear would be direct drive with a 1 to 1 ratio.

Think of the sprockets on a bicycle. A large one on the front that rotates as the bike is pedaled, and both a large and small sprocket on the back wheel with a chain that connects the front sprocket to the rear sprockets. As the gears are

changed, so is the mechanical advantage for the person that is pedaling In direct drive, the input speed and the output speed are the same; there is no gear reduction. Modern vehicles have overdrive, which is a ratio of 0.75 to 1. It means that the input speed is less than the output speed, which results in better fuel economy in modern vehicles.

These numbers and ratios are used to present the general idea. Every vehicle has its input to output ratios.

The drive line (or drive shaft) is a round tube that transfers power from the transmission to a differential. It is situated longitudinally underneath the car. A front-wheel drive vehicle wont have a drive shaft. Some four-wheel drive vehicles have more than one drive shaft.

A differential (aka rear differential in rear-wheel drive vehicles, back end, or part of the rear axle) has hypoid gears. These specialized gears transmit the rotation of the drive shaft 90 degrees to turn the axles and correlating wheels and tires. There are spider gears inside the center section of the differential that allow the wheels to travel different distances while turning. Consider a car that is turning right. The drivers side rear wheel travels farther than the passenger side rear wheel. Think of using a protractor to draw a circle. One leg of the protractor rotates on one central spot while the other leg pulls the process. While the rear wheels of a vehicle dont turn as sharply as a protractor, the principle is the same.

 

A differential for a German vehicle with cutout to see the inside.
A differential for a German vehicle with a cutout to see the inside.

 

An illustration of a differential which shows how the gears can be used to change the direction of therotation. The drive shaft is on the lower right corner of the image. The top right and lower left of the image show the rear axle which extends to the rear wheels.
The drive shaft is in the lower right corner of the image. The image’s top right and lower left show the rear axle extending to the rear wheels.

 

The Difference Between a Manual and Automatic Transmission:

A manual transmission (also called a standard transmission) uses conventional gears. All of these gears are turning at all times when the engine is running, and the clutch is released. When a gear is selected with the gear shift, the gear is
attached to the output shaft. Then to change gears, the clutch is depressed, and the next bag is selected, which attaches that gear to the output shaft. The kits are chosen manually.

 

Illustration of a manual transmission.
Illustration of a manual transmission.

 

An automatic transmission uses sunn and planet gears. A sun and planet gear set has a central Sun gear with planetary gears (typically three or four) located around the sun gear. These gears can rotate, turn or hold to create different speeds and directions. A valve body hydraulically applies multiple clutch packs and bands to control gear selection.

 

Illustration of sun and planet gears in an automatic transmission. The yellow gear in the illustration is thesun gear and the four violet gears surrounding the sun gear are the planet gears.
The yellow gear in the illustration is the sun gear, and the four violet gears surrounding the sun gear are the planet gears..

 

Types of Automatic Transmission Fluid:

There are 30 or more different types of transmission fluid for today’s modern vehicles. All the juices look the same. Refer to the owner’s manual to select the correct fluid. Aftermarket suppliers make fluids that are compatible with multiple different vehicles. When choosing aftermarket fluids, be sure that the specified fluid in the owner’s manual is listed on the aftermarket bottle.

Lubricants Used in Standard Transmission:

The lubricants used in a standard (or manual) transmission on modern vehicles have multiple types of fluid. Ensure the liquid in the car meets the manufacturer’s specifications.

Lubricants Used in Differentials:

Most differentials use conventional 80-90 gear oil. The 80-90 numbers indicate the weight and viscosity of the oil. Some vehicles require special fluids. Be sure the liquid meets the manufacturer’s specifications. Limited slip differentials may require an additional additive.

The Difference Between Front Wheel Drive, Rear Wheel Drive & Four Wheel Drive:

The main differences are the position of the drive train parts and where the drive train transmits the energy.

 

Illustration of a transaxle which has a transmission and a differential
Illustration of a transaxle which has a transmission and a differential

 

Front-wheel driveIncludes engine (red), and transaxle.
Front-wheel drive Includes engine (red), and transaxle.

 

A front-wheel drive vehicle, a transaxle, incorporates a differential and a transmission into one piece. The transaxle transmits power from the engine to the front wheels.

 

Rear-wheel driveIncludes engine (red), transmission, drive shaft, and rear differential.
Rear-wheel drive Includes the engine (red), transmission, drive shaft, and rear differential.

 

A rear wheel drive vehicle transmits engine power through a transmission to the drive shaft, and then to a differential in the rear of the vehicle.

 

Four-wheel driveIncludes engine (red), transmission, transfer case, front & rear drive lines, and front & rear differentials.
Four-wheel drive Includes engine (red), transmission, transfer case, front & rear drive lines, and front & rear differentials.

 

Alternate four-wheel driveIncludes engine (red), front transaxle, drive line, and rear differential.
Alternate four-wheel drive Includes engine (red), front transaxle, drive line, and rear differential.

 

It means that the input speed is less than the output speed, which results in better fuel economy in modern vehicles.

These numbers and ratios are used to present the general idea. Every vehicle has its input-to-output proportions.

The drive line (or drive shaft) is a round tube that transfers power from the transmission to a differential. It is situated longitudinally underneath the car. A front-wheel drive vehicle wont have a drive shaft. Some four-wheel drive vehicles have more than one drive shaft.

A differential (aka rear differential in rear-wheel drive vehicles, back end, or part of the rear axle) has hypoid gears. These specialized gears transmit the rotation of the drive shaft 90 degrees to turn the axles and correlating wheels and tires. There are spider gears inside the center section of the differential that allow the wheels to travel different distances while turning. Consider a car that is turning right. The drivers side rear wheel travels farther than the passenger side rear wheel. Think of using a protractor to draw a circle. One leg of the protractor rotates on one central spot while the other leg draws the process. While the rear wheels of a vehicle dont turn as sharply as a protractor, the principle is the same.

 

A differential for a German vehicle with a cutout to see the inside.

 

An illustration of a differential that shows how the gears can be used to change the direction of the rotation. The drive shaft is in the lower right corner of the image. The image’s top right and lower left show the rear axle extending to the rear wheels.

The Difference Between a Manual and Automatic Transmission:

A manual transmission (which is also called a standard transmission) uses conventional gears. All of these gears are turning at all times when the engine is running, and the clutch is released. When a gear is selected with the gear shift, the gear is
attached to the output shaft. Then to change gears, the clutch is depressed, and the next gear is selected, which attaches that gear to the output shaft. The gears are chosen manually.

 

Illustration of a manual transmission.

An automatic transmission uses sun and planet gears. A sun and planet gear set has a central sun gear with planetary gears (typically three or four) located around the sun gear. These gears can rotate, turn or hold to create different speeds and
directions. A valve body hydraulically applies multiple clutch packs and bands to control gear selection.

 

Illustration of sun and planet gears in an automatic transmission. The yellow gear in the illustration is the sun gear, and the four violet gears surrounding the sun gear are the planet gears.

Types of Automatic Transmission Fluid:

There are 30 or more different types of transmission fluid for today’s modern vehicles. All the fluids look the same. Refer to the owner’s manual to select the correct fluid. Aftermarket suppliers make fluids that are compatible with multiple different vehicles. When choosing aftermarket fluids, ensure the specified fluid in the owner’s manual is listed on the aftermarket bottle.

Lubricants Used in Standard Transmission:

The lubricants used in modern vehicles’ standard (or manual) transmissions have multiple fluid types. Ensure the fluid in the car meets the manufacturer’s specifications.

Lubricants Used in Differentials:

Most differentials use conventional 80-90 gear oil. The 80-90 numbers indicate the weight and viscosity of the oil. Some vehicles require special fluids. Be sure the fluid meets the manufacturer’s specifications. Limited slip differentials may require an additional additive.

The Difference Between Front Wheel Drive, Rear Wheel Drive & Four Wheel Drive:

The main differences are the position of the drive train parts and where the drive train transmits the energy.

 

Illustration of a transaxle that has a transmission and a differential

 

Front-wheel drive Includes the engine (red) and transaxle.

A front-wheel drive vehicle, a transaxle, incorporates a differential and a transmission into one piece. The transaxle transmits power from the engine to the front wheels.

 

Rear-wheel drive Includes the engine (red), transmission, drive shaft, and rear differential.

 

 

Four-wheel drive Includes engine (red), transmission, transfer case, front & rear drive lines, and front & rear differentials.

 

Alternate four-wheel drive Includes engine (red), front transaxle, drive line, and rear differential.

Leave a Comment

Your email address will not be published. Required fields are marked *

Select the fields to be shown. Others will be hidden. Drag and drop to rearrange the order.
  • Image
  • SKU
  • Rating
  • Price
  • Stock
  • Availability
  • Add to cart
  • Description
  • Content
  • Weight
  • Dimensions
  • Additional information
  • Sold
  • Shipping
Click outside to hide the comparison bar
Compare
0
0