Driveline Vibration and Service Chapter 79

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

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

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

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

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

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

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

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

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

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