This document provides an overview of the drive train, also called the power train, which transfers power from the engine to the wheels. It lists the key components of the drive train as the transmission, drive shaft or drive line, and differential. It then explains how each component works, such as how a transmission uses gears to provide different output ratios to the wheels, and how the differential allows the outside wheel to turn faster than the inside wheel during a turn. The document aims to help readers understand the basic functioning of the drive train.

1. Free Auto Repair Classes.
Lesson 9: The Drive Train
Jeff Crawford
Crawford’s Auto Repair

2.  The Drive Train is also called the Power
Train
 Parts include:
◦ Transmission
◦ Drive Shaft (or drive line)
 (in 4-wheel or rear-wheel drive vehicle, described
later)
◦ Differential
The Drive Train

3. Recall Chapter 5

4. Input from Engine to Transmission

5.  A transmission has gears (like a bicycle)
which provide different output ratios.
Transmission Gears and Output

6.  The ratio is the input of the crankshaft to
the output of the transmission
 1st Gear might have a 4:1 ratio
◦ (4,000 RPM input would have 1,000 RPM
output)
 2nd Gear might have a 3:1 ratio
 3rd Gear might have a 2:1 ratio
 4th Gear might have a 1:1 ratio
◦ Aka direct drive, there is no gear reduction
 Overdrive, 0.75:1 ratio (better gas
mileage)
Output Ratios

10. Transmissions have gears

11.  Automatic Transmission has “sun and
planet” gears
Automatic vs Manual

12.  Manual or Standard Transmission has
conventional gears that are always
turning when engine is running and clutch
is released
Manual Transmission

14.  Driveshaft connects transmission to rear
differential
Driveshaft

15.  Differentials have gears
◦ Transmit the direction of power 90 degrees
(from driveshaft to axle)
◦ Allow an outside tire to turn faster than an
inside tire during a turn
Differentials

18. Front-wheel drive vs
Rear-wheel drive vs
4-wheel drive

19.  Transmission and differential combined
into one piece called a transaxle
Front Wheel Drive

22.  Notice the
transfer case
and 2 drive
shafts in top
image.
 Which do you
expect is a
truck vs a
sedan with 4-
wheel drive
for the snow?

23. Questions?

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s-auto-repair-guide-free-ebook/
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