1. Driveline Vibration and Service
Chapter 79

2. Objectives Understand terms related to vibration
Describe the different types of vibration
Test for vibration using test instruments
Check driveshaft runout
Balance a driveshaft
Check driveshaft angle

3. Vibration Analysis NVH (noise, vibration, and harshness)
Specialty area of repair
Tire and wheel imbalance
Most common cause of vibration concerns
Process of elimination is used to analyze vibration problems
Vibration: part in motion in waves or cycles
Frequency: number of cycles in a period of time
Measured in cycles per second or hertz
Amplitude: vibration intensity
Velocity: combination of amplitude and frequency

8. Vibration Analysis (cont'd.)
Resonant or natural frequency
Frequency at which a body vibrates
Older unibody vehicles often have inherent vibration characteristics
Severity of vibration
Greatest at its point of resonance
Suspension frequency always the same
Out of balance driveshaft will have a frequency that can equal suspension frequency at a particular speed

10. Types of Vibrations First order vibration Second order vibration
Anything that spins at driveshaft speed and vibrates once every revolution
Second order vibration
Universal joint
Beat/boom vibration
One vibration interacts with another

11. Vibration Test Instruments
Reed tachometer
Senses frequency vibrations from ten to 80 Hz
Two rows of reeds of different lengths
Reeds vibrate at different frequencies
Electronic vibration analyzer (EVA)
Pickup held in place with Velcro®, putty, or a magnet
Larger reading means worse vibration
Handy when vibration occurs quickly and ceases
Used for balancing driveshafts

13. Vibration and Frequency (cont'd.)
During road test
Use a process of elimination
Vibration usually occurs at a specific rpm and goes away at other speeds
Drive in high gear at engine rpm where vibration is worst
Put into different gear to see if vibration changes
To test first order vibration
Raise tires in the air and run engine in gear to check driveline
Check front and rear while driveshaft is spinning

14. Driveshaft Runout Excessive runout in driveshaft Driveshafts
Caused by driveshaft or pinion flange
Measure runout of driveshaft
Mark high spot on shaft
Remove and remount 180 degrees away on flange
Runout is the same: shaft is at fault
Otherwise: flange is at fault
Driveshafts
Can be aluminum, steel, carbon fiber bonded to aluminum yokes, or composite

16. Other Causes of Vibration
Example: engine accessories
Eliminate out side causes of vibrations
Vibration present when car is not moving
Not a driveline problem
Engine accessory brackets
Designed to excite at 400 Hz or higher
Engine, torque converter, and driveshaft
Change in frequency as rpm changes
Rebuilt torque converter: often source of vibration
Check that muffler is not vibrating against frame

17. Driveshaft Balance Driveshafts are balanced on the ends
Weights welded onto ends of driveshaft at least one inch down shaft from weld
Power takeoffs and shafts that spin at under 1000 rpm need not be balanced
Correct imbalance with strobe-type balancer
Transducer tests driveshaft imbalance
Magnet that is spring-loaded on both sides
Moves back and forth in wire coil
Driveshaft balance can also be checked without special instruments

23. Driveshaft Angle
Angle of transmission output shaft and front of differential
Should be within a half degree of each other
Working angle
Difference between driveshaft angle and angle of transmission or differential
Launch shudder
Occurs on acceleration
Disappears around 25 mph
Several methods to measure driveshaft angle