Understanding Your Car's Drive Train

What is a Drive Train?

The drive train serves two primary functions: it transmits power from the engine to the drive wheels and varies the amount of torque. "Power" refers to the rate at which work is performed, while "torque" is the turning or twisting force. Multiple ratio gearboxes are essential because the engine delivers its maximum power at specific speeds, or RPM (Rotations Per Minute). To use the same engine RPMs at different road speeds, the "Gear Ratio" between the engine and the drive wheels must be adjusted.

Components of the Drive Train

Transmission

The transmission is a speed and power-changing device installed between the engine and the driving wheels. It allows the gear ratio to be adjusted to best meet each driving situation. There are two main types of transmissions:

Manual Transmission

Manual transmissions typically have four or five speeds and often include "overdrive," which allows the output shaft to turn faster than the input shaft for better fuel economy on highways. Some modern cars feature a "clutchless" manual transmission, which uses a stick shift and an automatic electric clutch. Speed and position sensors, mini-computers, and throttle controls prevent the engine from over-revving when the driver shifts gears.

Automatic Transmission

Automatic transmissions usually have three forward gears to balance speed and torque. In a three-speed transmission:

• First gear delivers maximum torque and minimum speed for starting.
• Second gear offers medium torque and speed for acceleration and hill climbing.
• Third gear allows maximum speed with minimum torque for highway travel.
• Reverse gear permits backward movement.

Differential

The differential allows the drive wheels to turn at different speeds, which is crucial when the vehicle is turning. It ensures that the outer wheel, which travels a greater distance, rotates faster than the inner wheel.

Transaxle

Some drive train layouts use a "transaxle," a combination of the transmission and the differential. Transaxles are commonly found in front-wheel-drive cars but are also used in mid- and rear-engine cars. Some exotic cars have their engine in the front and a transaxle in the rear for better weight balance.

Clutch and Torque Converter

A clutch allows the engine to continue rotating while the gears and wheels are stationary. Automatic transmission cars use a "torque converter" instead of a clutch.

Axle

In rear-wheel-drive cars, the axle is located in the rear. Engine power is transmitted from the transmission to the axle via the drive shaft, a metal tube with joints on each end called universal joints. These joints allow the tube to move in relation to the suspension while maintaining power flow to the rear. In front-wheel-drive cars, the axle is integrated into the transmission, hence the term "transaxle."

Common Problems and Preventive Maintenance

Common Problems

• Manual Transmissions: Wear mainly occurs in the synchronizers, which make shifting easier and prevent gear clash. Over time, the synchronizers, made of brass, can wear out, causing hard shifting and grinding.
• Automatic Transmissions: Wear can cause slipping and uneven shifting patterns. Universal joints can wear and cause vibrations while driving. Many newer universal joints are sealed and cannot be lubricated, requiring replacement.

Preventive Maintenance

• Change Transmission Fluid: Follow the recommended intervals in your owner's manual. If you tow a boat or trailer, change the fluid more frequently.
• Avoid "Riding" the Clutch: For manual transmissions, release the clutch smoothly without revving the engine excessively.
• Install a Transmission Cooler: If you tow a boat or trailer, consider installing a transmission cooler for your automatic transmission to prevent overheating.
• Lubricate Universal Joints: Ensure your universal joints are lubricated during oil changes if they are the type that can be lubricated. When replacing universal joints, opt for ones with lubrication fittings.
• Avoid Full Lock Turns: For front-wheel-drive cars, avoid applying full throttle while the wheels are turned at full lock to prevent stress on the universals.

What to Discuss with Your Mechanic

If you notice a vibration while driving, describe when it occurs (e.g., while accelerating, braking, maintaining speed, or turning) to your mechanic. This information can help diagnose the issue more accurately.

Interesting Stats

• Transmission Failure Rates: According to a study by Consumer Reports, about 1 in 10 vehicles will experience a transmission failure by the time they reach 100,000 miles source.
• Fuel Economy: Vehicles with manual transmissions can be up to 5% more fuel-efficient than their automatic counterparts source.

Understanding your car's drive train can help you maintain it better and identify issues early. Regular maintenance and being aware of common problems can extend the life of your vehicle's drive train components.

This article is based on information from the Auto Insight program, available online from AutoEducation.com.