Vibration Diagnosis and Correction
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Cadillac Tech Tips - How to fix it Discussion, Vibration Diagnosis and Correction in Item Specific Cadillac Discussion; Systematic Approach Diagnostic Information and Procedures Tire and Wheel Inspection Road Test Types of Road Test Classifying the Vibration Vibrations ...
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    Vibration Diagnosis and Correction

    Systematic Approach
    Diagnostic Information and Procedures
    Tire and Wheel Inspection
    Road Test
    Types of Road Test
    Classifying the Vibration
    Vibrations That Can Be Felt
    Vibrations That Make Noise
    Matching Frequency to Component RPM
    Rotor/Drum Imbalance
    Front Wheel Driveline Vibrations
    Engine Related Vibration
    Tire and Wheel Vibration

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    Re: Vibration Diagnosis and Correction

    Systematic Approach
    During the last 10-15 years, vehicle design and engineering have dramatically changed due to the following factors:

    Increased fuel costs
    Decreased fuel supplies
    Corporate Average Fuel Economy requirements
    Clean air legislation
    Foreign competition
    Ability to withstand collision
    Rising customer expectations
    Most Vehicle designs have evolved from full-frame construction to lighter unibody designs. These designs transfer noise and vibration much more readily.

    During this same period, options such as the following have become increasingly popular:

    Air conditioning
    Power steering
    All-wheel or four wheel drive
    Such options increase engine load and can also generate unwanted noise and vibration.

    Customer perception of quality can be directly linked to the presence or absence of unwanted noise and vibration. A technician's ability to quickly diagnose and repair a noise or vibration directly affects that customer's loyalty to the dealership.

    The intent of this sub-section of the service manual is to provide a systematic approach to vehicle vibration diagnosis and correction. By using Strategy Based Diagnosis and troubleshooting philosophies covered in this sub-section, technicians will be able to provide effective and timely repairs.


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    Re: Vibration Diagnosis and Correction

    Diagnostic Information and Procedures
    This section describes the techniques and procedures for correcting the following types of vibrations:

    Tire and wheel shake
    Launch shudder
    Exhaust moan
    Engine firing frequency
    Drive line vibration
    Identifying the Concern
    The first step in diagnosing a vibration concern is to identify the exact vibration that concerns the customer.

    Sometimes the vibration can be duplicated at a given speed. Other vibrations may not be as evident and may require questioning the customer carefully. Perform a road test with the customer in the vehicle in order to determine the specific vibration complaint.

    Ask the following questions when attempting to identify a vibration complaint:

    At what speed is the vibration the worst?
    Can the customer feel the vibration? If so, where?
    Can the customer hear the vibration?
    Does the engine or the vehicle load affect the vibration?
    Does the vibration occur in more than one gear range?
    When did the vibration first appear?
    The answers to these questions will help in duplicating and diagnosing the vibration.

    If you suspect that the vibration is normal, compare the vibration with a vehicle that is equipped in the same way, including the following factors:

    Body style
    Engine option
    Engine driven accessories
    Transmission type
    Tire size
    Suspension performance type
    Axle ratio

    Important
    Do NOT attempt to repair a normal condition, or the customer will probably be convinced that the vehicle has a problem. Customer satisfaction becomes extremely difficult after this point.


    If necessary, ride with the customer. Make the comparison with the customer present and explain the situation.

    Duplicate the Condition
    All vehicles produce vibrations. Some vibrations are normal, while others are not. Some vibrations can be repaired, some cannot. Duplicate or experience the customer's complaint. Evaluate the vibration and the cause of the vibration under changing conditions. Otherwise, you cannot know for certain that you are fixing what the customer would like fixed.

    The symptoms and characteristics of a noise or vibration are also important information. Ask yourself the following questions before you begin:

    What does the vibration feel like?
    Does the vibration make noise? If so, what does the vibration sound like?
    Different types of noise and vibration have particular characteristics. These characteristics will help determine the cause of the condition and the best way to correct the condition.

    A Process of Elimination
    You must understand a few basic concepts before attempting to diagnose a vibration. As in any diagnostic process, you must perform the following steps:

    Gather the information
    Decipher the information
    Make your correction based on the results
    Road test the vehicle and inspect the vehicle in a manner which systematically eliminates different components. This process supplements the information which you have received from the customer concerning the complaint. Concentrating efforts on the areas that have not been eliminated will make repairs faster and more effective.

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    Re: Vibration Diagnosis and Correction

    Tire and Wheel Inspection



    The tires on all new production models have a tire performance criteria (TPC) rating number molded on the sidewall. The TPC rating will appear as a 4-digit number preceded by the letters TPC SPEC on the tire wall near the tire size. A replacement tire should have the same TPC rating.

    FIGURE Tire Wear(c)




    (1) Hard Cornering/Underinflation
    (2) Incorrect Alignment/Lack of Rotation
    (3) Incorrect Alignment/Non-uniform Tire
    (4) Heavy Acceleration/Over inflation
    (5) Wear Indicator


    Inspect the tire and wheel assemblies for the following conditions:

    Unusual wear such as cupping, flat spots, and heel-and-toe wear. (These conditions can cause tire growl, howl, slapping noises, and vibrations throughout the vehicle.)
    Proper inflation
    Bulges in the sidewalls (Do not confuse bulges with normal ply splices, commonly seen as indentations in the sidewall.)
    Bent rim flanges
    By inspecting these characteristics of the tire and wheel assemblies, you may discover the cause of the vibration. The inspection will also provide assurance that the vehicle is safe for road testing.

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    Re: Vibration Diagnosis and Correction

    Road Test
    Purpose of Road Testing

    Important
    Do NOT attempt to repair a normal condition, or the customer will probably be convinced that the vehicle has a problem. Customer satisfaction becomes extremely difficult after this point.


    The purpose of road testing is to duplicate the vibration complaint and to find any operating conditions that change or eliminate the vibration. Most importantly, road testing will determine whether the vibration is related to the engine speed or to the vehicle speed.

    In order to complete a quick and accurate road test, install an engine tachometer (such as a scan tool) and the Electronic Vibration Analyzer (EVA) in the vehicle. Place the EVA vibration sensor in a location where the customer's concern can be felt.

    Determining the Component Group
    After you have related a vibration to either the engine speed or to the vehicle speed, break the vibration down further in order to fit into one of the following groups of rotating components:

    The engine, the clutch disc (manual transmission), the transmission flywheel (automatic transmission), and the transmission torque converter.
    The transmission output shaft, the propeller shaft, and the rear axle differential pinion.
    The tires, the wheels, the hubs, the drums, and the rotors.
    These three groups represent the major areas that can produce vibration complaints. The components in each group are related to each other because the components are either bolted or splined together. This means that each group of components rotates at the exact same speed.

    These categories can be broken down further in order to identify the exact component responsible for the disturbance. The emphasis is on testing in order to pinpoint the source and to eliminate unnecessary parts replacement.

    Perform a road test for ALL vibration complaints unless the disturbance occurs only with the vehicle at a standstill.


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    Re: Vibration Diagnosis and Correction

    Types of Road Test

    Caution: Road test a vehicle under safe conditions and while obeying all traffic laws. Do not attempt any maneuvers that could jeopardize vehicle control. Failure to adhere to these precautions could lead to serious personal injury and vehicle damage.

    Important: Before performing any road test, inspect the tires and wheels. Refer to Tire and Wheel Inspection .

    The following road test procedures are the most informative and the most used:

    • Slow acceleration test

    • Neutral coast-down test

    • Downshift test

    • Neutral run-up test

    • Brake torque test

    • Steering input test

    • Standing start acceleration test (launch shudder)

    These tests will help to pinpoint the vibration. Perform all of the tests on a smooth, level road.

    Slow Acceleration Test
    This test will identify those conditions which are related to the engine-speed or to the vehicle-speed. Additional tests may be necessary in order to determine the exact cause of the vibration.

    Caution: Road test a vehicle under safe conditions and while obeying all traffic laws. Do not attempt any maneuvers that could jeopardize vehicle control. Failure to adhere to these precautions could lead to serious personal injury and vehicle damage.


    On a smooth, level road, slowly accelerate up to highway speed.
    Look for disturbances that match the customer's description.
    Observe the following readings where the disturbance occurs:
    • The vehicle speed, km/h (mph)

    • The engine speed (RPM)

    • The frequency (if possible)

    Now perform the neutral coast-down test and the downshift test.

    Neutral Coast-Down Test

    Caution: Road test a vehicle under safe conditions and while obeying all traffic laws. Do not attempt any maneuvers that could jeopardize vehicle control. Failure to adhere to these precautions could lead to serious personal injury and vehicle damage.

    On a smooth level road, accelerate to a speed slightly higher than the speed at which the vibration occurs.
    Shift the vehicle into NEUTRAL gear and coast down through the vibration range.
    Observe whether the vibration is present in NEUTRAL gear.

    If the vibration still occurs in NEUTRAL gear, then the vibration is definitely sensitive to vehicle-speed. At this point, the following components have been eliminated as a cause of the vibration:

    • The engine

    • The clutch disc (manual transmission)

    • The transmission flywheel (automatic transmission)

    • The torque converter

    Depending on the symptoms or the frequency, the repair will concentrate on one of the following components:

    • The tire and wheel assemblies

    • The transmission output shaft

    • The propeller shaft

    • The rear axle differential pinion

    • The rear drive axle or the rear drive axle shafts

    Downshift Test

    Caution: Road test a vehicle under safe conditions and while obeying all traffic laws. Do not attempt any maneuvers that could jeopardize vehicle control. Failure to adhere to these precautions could lead to serious personal injury and vehicle damage.

    On a smooth, level road, accelerate to the speed at which the concern vibration occurs.
    Observe the engine RPM.

    Decelerate and safely downshift to the next lower gear.
    Operate the vehicle at the previous engine RPM.
    If the vibration returns at the same engine RPM, the following conditions are the most probable causes of the vibration:

    • The engine

    • The clutch disc (manual transmission)

    • The propeller shaft

    • The transmission flywheel (automatic transmission)

    • The torque converter

    Repeat this test in lower gears, and in NEUTRAL gear, in order to confirm the results.

    In some cases, a vibration may also be sensitive to torque or engine load, as well as being related to a specific engine speed or vehicle speed. These vibrations can be most difficult to diagnose, and require additional testing. A systematic approach usually leads to isolating the problem.

    Neutral Run-Up Test
    This test is designed to identify vibrations which are related to the speed of the engine. Use this test when the customer has a concern with vibration at idle, or as a follow-up to the downshift test. This test probably doesn't apply when the complaint is related to vehicle speed only (appearing at the same vehicle speed regardless of the engine speed).

    Caution: Road test a vehicle under safe conditions and while obeying all traffic laws. Do not attempt any maneuvers that could jeopardize vehicle control. Failure to adhere to these precautions could lead to serious personal injury and vehicle damage.

    Slowly increase the engine speed while looking for disturbances that match the customer's complaint.
    Observe the engine speed (RPM) and the frequency (if possible) where the vibration occurs.

    Brake Torque Test
    This test is designed to identify engine-related vibrations that were not uncovered with the neutral run-up test. This test also works for vibrations that are sensitive to the engine load or to the torque. This test will probably not apply to vibrations which are related only to the speed of the vehicle.

    Caution: Road test a vehicle under safe conditions and while obeying all traffic laws. Do not attempt any maneuvers that could jeopardize vehicle control. Failure to adhere to these precautions could lead to serious personal injury and vehicle damage.
    1. Apply the park brake.
    2. Block the front wheels.
    3. Step firmly on the brake pedal.
    4. Place the vehicle in DRIVE.
    5. Slowly increase the engine speed while looking for vibrations that match the customer's description.
    6. Observe the engine speed (RPM) and the frequency (if possible) at which the disturbance occurs.
    7. If necessary, place the vehicle in REVERSE gear and repeat steps 5 and 6.

    Steering Input Test
    This test is intended to determine how much the wheel bearings and other suspension components contribute to the vibration, especially a vibration relating to noise, such as growl, grinding, and roaring.

    Caution: Road test a vehicle under safe conditions and while obeying all traffic laws. Do not attempt any maneuvers that could jeopardize vehicle control. Failure to adhere to these precautions could lead to serious personal injury and vehicle damage.
    1. With the vehicle at the vibration speed (mph), drive through slow sweeping turns, first in one direction and then in the other direction.
    2. If the vibration gets worse or if the vibration goes away, inspect the following components as possible causes of the vibration:
    • The wheel bearings

    • The hubs

    • The tire tread

    The CV joint angle increases when the vehicle is turning. On front weel drive (FWD) and four wheel drive (4WD) vehicles, CV joint condition systems may appear when the angle increases. Putting a load on the CV joint may increase the vibration amplitude. The third order, tire speed related amplitude would remain the same.

    Standing Start Acceleration (Launch Shudder) Test
    The purpose of this test is to duplicate a vibration called launch shudder. In some cases, a powertrain mount or an exhaust ground-out may also be the cause of the vibration, depending on the symptoms.

    Caution: Road test a vehicle under safe conditions and while obeying all traffic laws. Do not attempt any maneuvers that could jeopardize vehicle control. Failure to adhere to these precautions could lead to serious personal injury and vehicle damage.
    1. With the vehicle at a complete stop and in gear, remove your foot from the brake pedal.
    2. Accelerate to 48-64 km/h (30-40 mph) while looking for vibrations that match the customer's description.
    3. Other possible causes of launch shudder include the following conditions:

    • Incorrect trim height.

    • A worn or damaged drive axle CV joint

    • A ground-out through the engine or transmission mounts

    • Faulty exhaust hangers and mounts

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    Re: Vibration Diagnosis and Correction

    Classifying the Vibration
    The next step after road testing the vehicle is to identify the frequency of the duplicated and abnormal vibration. Use the EVA in order to measure the frequency. If the EVA is not available, observe how the vibration feels or sounds. The majority of vibrations will fit into one of the following categories.

    • Vibrations that can be felt:

    - Shake

    - Roughness

    - Buzz

    - Tingling

    • Vibrations that make noise:

    - Boom

    - Moan and groan

    - Howl

    - Whine

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    Re: Vibration Diagnosis and Correction

    Vibrations That Can Be Felt
    Shake




    Shake is a low frequency vibration, typically 5-25 Hz. Shake is sometimes felt in the steering wheel, the seat, or the console. The best description is the feeling from an out-of-round or unbalanced tire. Customers may refer to a shake in one of the following terms:

    Shimmy
    Wobble
    Shudder
    Waddle
    Hop
    In most cases, shake is caused by damage or wear to the following components:

    The tires
    The wheels
    The brake rotors (vehicle-speed sensitive)
    The steering tie rod ends
    The suspension ball joints
    The engine (engine-speed sensitive)
    Roughness
    Roughness is a vibration with a slightly higher frequency than the shake, usually 25-50 Hz. Roughness is similar to the feeling you get from holding a jigsaw.

    Buzz
    Buzz is slightly higher in frequency, usually 50-100 Hz. A buzz is similar to the feel of an electric razor. You may feel it in your hands through the steering wheel, in your feet through the floor, or in the seat. Inspect the following components for a possible cause:

    The exhaust system
    The A/C compressor
    The engine

    Tingling
    This is the highest vibration frequency that you can feel. Tingling may sometimes produce a pins and needles sensation. Customers may say the vibration creates numbness in their hands or feet.

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    Re: Vibration Diagnosis and Correction

    Vibrations That Make Noise
    Boom
    Boom is a low frequency interior noise of 20-60 Hz. Sometimes the customers complain of a pressure in their ears. Examples of similar noises include a bowling ball rolling down an alley, deep thunder, or a bass drum.


    A customer may use the following words to describe boom:

    Droning
    Growling
    Moaning
    Roaring
    Rumbling
    Humming
    Boom may be accompanied by a perceptible vibration (roughness).

    Moan or Groan
    Moan or Groan is a sustained tone at a low frequency of 60-120 Hz, somewhat higher than boom.

    Examples of similar noises include a bumble bee or blowing air across the top of a soda bottle. A customer may use the following words to describe moan or drone:

    Humming
    Buzzing
    Resonance
    Moan or Groan may be accompanied by a perceptible buzzing vibration. Inspect the following systems:

    The powertrain mounts
    The exhaust system

    Howl
    Howl is a noise at mid-range frequency of 120-300 Hz. This sounds like the wind howling.

    Whine
    Whine is a prolonged, high-pitched sound in the 300-500 Hz range. Whine is usually related to the meshing gears or gear noise. Similar sounds include mosquitoes, turbine engines, and vacuum cleaners.

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    Re: Vibration Diagnosis and Correction

    Matching Frequency to Component RPM
    At this point in the diagnosis, the vibration has gone through the following analysis:

    • The vibration has been duplicated.

    • The vibration has been designated as abnormal.

    • The vibration has been related either to engine speed or to vehicle speed.

    • The vibration has been assigned a frequency from the Smart Electronic Vibration Analyzer (Smart EVA) or identified based on its feel or its sound.

    Automotive vibrations are usually related to the rotating speed of a component. Calculate the speed of these components using either an engine speed method or a vehicle speed method. Use the engine RPM readings taken during the road test in order to diagnose the vibrations that are sensitive to engine speed.

    If the vibration is sensitive to vehicle speed, determine the rotational speed of the tires. As long as you operate the vehicle at a constant speed, the tires will operate at a constant speed. This speed is measured in rotations, or cycles per second. The reading is then compared to the frequency of the vibration, which is also measured in cycles per second.

    Calculating Tire Rotation
    The Smart EVA program is designed to perform targeted frequency calculations on a suspected vibration source. The tire size, axle ratio, number of cylinders, vehicle speed and engine rpm are factored into a calculation that determines the predominant vibration frequency, amplitude and the suspected vehicle system producing the vibration.
    1. Use the Smart EVA to determine the speed at which the vibration occurs.
    2. From the main menu, select Auto Mode, then click enter; select Vehicle Speed, then click enter.
    3. Enter the vehicle tire size information with one of three options:
    4. - RPS at 5 mph -- Refer to the Tire/Speed table below for the Hertz value at 8 km/h (5 mph) for that tire size.
    5. - Database -- Select the tire type and tire size from each selection screen. Tip: when browsing the tire size or axle ratio list, press a number key to go to a related point in the list; for example, press 1 to go to the top of the list; press 4 or 5 to go to the middle of the list; press 9 to go to the bottom of the list.
    6. - Manual Entry -- Select Manual Entry when the vehicle is fitted with speciality tires. Enter the tire width (100-500 mm), aspect ratio (0.30-1.50) and rim diameter (10.00-25.00 in).
    7. Enter the driveshaft configuration.
    8. Enter the axle ratio, refer to the Axle Ratio table below,(2.00-9.00) from the Axle Ratio selection screen. Note: Axle Ratio is not applicable if front wheel drive (FWD) is selected.
    9. Select the vehicle speed units in miles-per-hour (MPH) or Kilometers-per-hour (KPH).
    10. Enter the vehicle speed at which the vibration is felt.
    11. As the test is run, the vehicle speed must be manually adjusted to match the actual vehicle speed:
    12. - Select the incremental step you want to increase/decrease vehicle speed, then click enter.
    13. - View the frequency ranges applicable for the speed selected, press enter to go to the active data screen or exit to go back and reselect the speed if you are not within a valid range.
    14. - Click the up or the down key to adjust the on-screen vehicle speed on the live data screen to match the actual vehicle speed.
    15. Data is displayed as averaged (A is displayed) or instantaneous (I is displayed). Press key 8 to toggle. The amplitudes of the vibrations detected are displayed in descending order beginning with line 2. Repair the strongest vibration first. One to three sources of vibration are identified:
    16. - TIRE 1,2,3 or 4 (1st, 2nd, 3rd or 4th order tire/wheel system concern).
    17. - PROP 1 or 2 (Propshaft concern).
    18. - OVERLAP (overlap of Tire 3 and Prop 1 frequencies).
    19. - UNKNOWN (vibration source is unknown).
    20. Data is received through input A (A is displayed) or B (B is displayed). Press key 4 to toggle.
    21. The vehicle speed (V) is displayed in mph or kph. Press the down or up key to manually adjust this figure to match actual vehicle speed.
    22. An identification letter symbol displays during record (R) or playback (P).
    23. During record or playback the event and frame numbers are displayed. If an event is not selected, a "?" appears. During record or playback the frame number cycles from 0 to 9; for example, 0:0, 0:1, 0:2...0:9.
    24. Amplitude of the signal is displayed in number of G forces (G).

    Steering and Suspension Assembly Vibrations
    Steering and suspension assembly vibrations are the first level of testing for low-frequency vibrations that are sensitive to vehicle speed. The symptoms of a steering/suspension first-order vibration are a shimmy or a shake. This is usually felt in the steering wheel or in the seat. Inspect the following components for wear or damage:

    • The steering tie rod ends.

    • The suspension ball joints.

    • The tires.

    • The wheels.

    • The brake rotors (vehicle-speed sensitive).

    • The engine (engine-speed sensitive).


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    Re: Vibration Diagnosis and Correction

    Rotor/Drum Imbalance
    Rotors and drums do not have a set tolerance. However, rotors or drums with more than 21 g (0.75 ounce) imbalance have the potential to cause vibration. Inspect the rotors and the drums for imbalance using either the on-vehicle or the off-vehicle method.

    Checking Rotor/Drum Imbalance (On-Vehicle)
    Support the vehicle rear axle on a suitable hoist. Refer to Lifting and Jacking the Vehicle in General Information.
    Remove the rear tire and wheel assemblies. Refer to Tire and Wheel Removal and Installation in Tires and Wheels.

    Caution: One or more of the following guidelines may apply when performing specific required tests in the work stall:

    • When a test requires spinning the drive wheels with the vehicle jacked up, adhere to the following precautions:

    - Do not exceed 56 km/h (35 mph) when spinning one drive wheel with the other drive wheel stopped. This limit is necessary because the speedometer indicates only one-half the actual vehicle speed under these conditions. Personal injury may result from excessive wheel spinning.

    - If all of the drive wheels are spinning at the same speed, do not exceed 112 km/h (70 mph). Personal injury may result from excessive wheel spinning.

    - All persons should stay clear of the rotating components and the balance weight areas in order to avoid possible personal injury.

    - When running an engine in the repair stall for an extended period of time, use care not to overheat the engine and the transmission.

    • When a test requires jacking up the vehicle and running with the wheels and brake rotors removed, adhere to the following precautions:

    - Support the suspension at normal ride height.

    - Do not apply the brake with the brake rotors removed.

    - Do not place the transmission in PARK with the drive axles spinning.

    - Turn Off the ignition in order to stop the powertrain components from spinning.

    • When running an engine in the work stall, use the exhaust removal system to prevent breathing dangerous gases.


    Reinstall the wheel nuts in order to retain the rotors/drums.
    Run the vehicle at the complaint speed while inspecting for the vibration.
    If the vibration still exists, perform the following steps:
    Remove the rotors/drums.
    Run the vehicle back to speed.
    If the vibration is eliminated, perform the following steps:
    Remove the rotors/drums one at a time.
    Perform the vibration test for each rotor/drum.
    Replace the rotor/drum that is causing the imbalance.
    Inspect the balance of the new rotor/drum.
    Checking Rotor/Drum Imbalance (Off-Vehicle)
    Measure the diameter and the width of the rotor/drum.



    Mount the rotor/drum on a balancer in the same manner as a wheel.
    Important: You can only inspect the rotors/drums for static imbalance. Ignore the dynamic imbalance reading.


    Inspect for static imbalance.
    If the rotor/drum shows imbalance, replace the rotor/drum.
    Inspect the balance of the new rotor/drum before you install the rotor/drum on the vehicle.

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    Re: Vibration Diagnosis and Correction

    Front Wheel Driveline Vibrations
    Front wheel drive shafts have the following characteristics

    • The front wheel drive shafts are short.

    • The front wheel drive shafts have constant-velocity (CV) universal joints.

    • The front wheel drive shafts have low mass.

    • The front wheel drive shafts turn or spin at a lower rate of speed than the propeller shaft on a RWD vehicle.

    Although FWD is smoother than RWD, the following problem conditions may occur and require diagnosis and correction:

    • Launch shudder

    • Third-order tire-related vibrations

    • Growling (wheel bearing) noise

    • Clicking noise or shudder during turns

    Launch Shudder
    Launch shudder is a shaking sensation that is felt in the steering wheel and/or the front of the vehicle during moderate to heavy acceleration from a standing start. Launch shudder may also be a rocking back-and-forth motion in the vehicle during acceleration.

    On front-wheel-drive vehicles, launch shudder can be caused by the following conditions:

    • Worn or damaged inner tri-pot joints

    • Excessive inner joint angularity

    Excessive joint angles are usually the result of a front trim or a spring height that is set too high. A powertrain mounting that is damaged or misaligned can also create the following conditions:

    • Excessive joint angles

    • Launch shudder

    During fast acceleration, the front suspension height is raised by the high torque of the vehicle powertrain. When the suspension height rises, the inner tri-pod joint angles increase and can cause a launch shudder condition if one of the following conditions are present:

    • The joints are worn.

    • The angles are already excessive before acceleration.

    Because the inner tri-pot joint is usually the cause of launch shudder, the disturbance is typically related to third-order tire rotation frequency.

    Identify the type of disturbance.
    Visually inspect the drive axles for worn or damaged inner joints.
    If you detect no obvious problem, measure the trim or spring height in order to determine if the suspension is causing an excessive joint angle. Do not measure the body height. Body height measurements are not used because potential sheet metal variations could lead to mis-diagnosis of the problem cause. Trim height specifications are found in the vehicle service manual.
    If the spring height is out-of-specification, place sandbags under the following locations in order to lower the suspension:
    - Under the hood

    - Over the strut towers

    Caution: Road test a vehicle under safe conditions and while obeying all traffic laws. Do not attempt any maneuvers that could jeopardize vehicle control. Failure to adhere to these precautions could lead to serious personal injury and vehicle damage.

    Road test the vehicle, adding sandbags until you eliminate the disturbance.
    In order to lower the suspension, measure the spring height in order to determine the required springs to install.
    Each vehicle line has multiple spring options with different spring rates. You can achieve approximately 10 mm of suspension height change by dropping down one spring code. You can locate the spring codes in the following areas:

    • On the springs

    • On the SPID label in the vehicle

    Important: Always replace the springs in matching sets in order to insure correct body levels and proper suspension performance.

    You can find the list of available springs in the parts catalog.

    Third-Order Tire-Related Vibrations
    Tri-pot joints are so named because of their design characteristics. Tri-pot or tri-potal joints have three trunnions (or a trilobal spider assembly) that fit into a race or a cup. The assembly moves in and out freely in order to compensate for drive axle length changes during suspension travel.

    Although worn or damaged inner tri-pot joints can cause launch shudder, worn or damaged inner tri-pot joints may also cause vehicle speed-related, third-order tire vibrations.

    Third-order tire-related disturbances can occur if the following conditions are present:

    • The joint becomes worn or damaged.

    • The joint has excessive free-play or lash.

    The worn joint creates three disturbances per revolution of the axle shaft. Because the axle shaft turns at the same rate as the wheel, third-order tire-related vibrations will result.


    Growling (Wheel Bearing) Noise

    Front-wheel-drive (FWD) hub and bearing assemblies can make a low, growling noise that increases with the vehicle speed. The tires and the bearings can make a similar noise. The tires and bearings are vehicle-speed-sensitive.

    In order to differentiate between tire noise and bearing noise, drive the vehicle in a straight line and perform several turning maneuvers side-to-side. A worn wheel bearing typically exhibits increased noise during turns. If the noise level increases during a right-hand turn, then the left-hand wheel bearing generally is causing the problem. The opposite is true for a left-hand turn. If a bearing and not the tires is the cause of the disturbance, the noise level increases when turning because an added load is applied to the bearing with the fault.


    Clicking Noise or Shudder During Turns
    A clicking noise or a shudder during vehicle turns is usually a symptom caused by one of the following conditions:

    • A worn or damaged outer constant-velocity (CV) joint

    • A worn or damaged outboard CV joint

    During a visual inspection of the drive axle, look for a damaged boot on the outer CV joint. A damaged boot can allow water and other contaminants such as dust and dirt to compromise lubrication and prematurely destroy the joint. The CV joint will no longer function smoothly, causing the disturbance.

  14. #13
    AJxtcman's Avatar
    AJxtcman is offline Cadillac Owners Connoisseur
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    Re: Vibration Diagnosis and Correction

    Engine Related Vibration
    Engine vibration is usually due to one or more of the following conditions:

    • First-order engine imbalance

    • Inherent engine firing sequence

    • Inherent shaking engine forces

    • Engine-driven accessories

    Because these vibrations are engine-speed related, they are also normally torque sensitive. These vibrations may appear and disappear at different vehicle or road speeds, but will always appear at the same engine speed.

    For example, if a customer states that a vibration is present at 40 km/h (25 mph), 64 km/h (40 mph), and again at 104 km/h (65 mph), and that the symptoms of the vibration are similar at all of these speeds, the vibration is probably engine-speed related. Any disturbance or vibration that is present during the following road tests would be considered engine-speed related:

    • The Neutral run-up test

    • The downshift test

    • The brake torque test

    Any vibration that is present during the Neutral coast-down test is not engine-speed related. The engine-related vibrations covered in this diagnosis are engine-speed sensitive only.

    Skipped the rest

  15. #14
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    Re: Vibration Diagnosis and Correction

    Tire and Wheel Vibration

    Tire and wheel assembly vibrations are the next level of testing for low-frequency vibrations that are sensitive to vehicle speed. The tires, the wheels, the brake rotors, and the wheel hubs should be systematically tested, according to the symptoms.

    First-Order Tire and Wheel Assembly Vibration
    The following are symptoms of first-order vibrations caused by tire and wheel assemblies:

    • The vibration is always related to the speed of the vehicle. If the vibration is affected by the speed of the engine, or if the vibration is eliminated by placing the transmission in Neutral, the vibration is not related to the tire and wheel assemblies.

    • The vibration will feel like a shake, usually in the steering wheel or the seat.

    - Tire and wheel vibrations that are felt in the steering wheel are most likely related to the front tire and wheel assemblies.

    - Tire and wheel vibrations that are felt in the seat or the floor are most likely related to the rear tire and wheel assemblies. This may not always hold true, but this is a general rule that may serve to initially isolate a problem to the front or the rear of the vehicle.

    • The customer may complain of a waddle at low speeds of 8-56 km/h (5-35 mph).

    • The frequency on the EVA will correspond to the first-order of tire rotation. This frequency will usually be in the 10-20 Hz range, depending on the speed of the complaint and the size of the tire. The smaller the tire, the faster the tire will rotate at any given speed.

    • The range of the human ear begins at 20 Hz. For this reason, first-order tire vibrations rarely produce noise. The exception is when the tires display an irregular tread pattern or flat spots. This causes a growling or a slapping noise.

    Tire Runout Measurement
    Correct the runout problem first, because the runout of a tire/wheel assembly will directly affect the amount of imbalance and radial force variation. As the amount of runout decreases, imbalance and force variation also decrease.

    Important: Before measuring or attempting to correct excessive runout, carefully inspect the tire for an uneven bead seat. The distance from the edge of the ring to the concentric rim locating ring should be equal around the entire circumference. If the beads are not seated properly, remount the tire. Otherwise excessive runout and imbalance may result.


    You can correct radial and lateral runout at the same time. Two methods are available for measuring runout of the tire/wheel assemblies:

    • On the vehicle (mount the tire to the hub; the wheel bearing must be in good condition.)

    • Off the vehicle (mount the tire on a spin-type tire balancer)

    Make an initial on-car visual inspection prior to performing the off-car runout tests.

    Measuring the tire/wheel runout off the vehicle is the easier method for the following reasons:

    • A dial indicator can be more easily mounted in the correct location.

    • The chance of water, snow, dirt, or slush getting on the dial indicator is decreased. (A dial indicator is a very fragile and expensive tool that is used extensively in vibration repair work. Contamination by outside elements or rough handling will usually result in malfunction).

    Once you have measured and corrected the runout off the vehicle, a quick examination of runout on the vehicle will indicate if any further problems exist.

    If the off-vehicle measurement differs significantly from the on-vehicle measurement, the runout problem is due to one of the following:

    • Stud circle runout

    • Hub flange runout

    • A mounting problem between the wheel and the vehicle.

    Measuring Tire Runout
    If a vehicle sits in one place for an extended period of time, flat spots may develop at the point where the tires rest upon the ground. These flat spots will affect the runout readings. Before you take any runout measurements, eliminate these flat spots by driving the vehicle long enough to warm up the tires.
    1. Lift the vehicle on a hoist or support the vehicle with jackstands. Refer to Lifting and Jacking the Vehicle in General Information.
    2. In order to get an initial indication of how much runout exists, spin each tire and wheel on the vehicle by hand. You may also use the engine at a slow speed in order to drive the wheels. Visually inspect the amount of runout from the front or the rear.
    3. Mark the location of each tire/wheel assembly in relation to the wheel studs and to their position on the vehicle for future reference.
    4. Remove the tire/wheel assemblies one at a time. Mount each assembly on a spin-type wheel balancer. Locate the tire/wheel assembly on the balancer with a cone through the back side of the center pilot hole.
    5. For lateral runout place the dial indicator in a smooth area on the tire sidewall as close to the tread as possible.
    FIGURE Lateral Tire Runout(c)

    1.gif

    FIGURE Radial Tire Runout(c)

    2.gif

    Measure the tire/wheel assembly runout as shown in the figure.

    For radial runout, wrap the outer circumference with tape (1) when you measure the radial runout. This allows for a smooth reading from the dial indicator.

    Ignore any jumps or dips due to sidewall splices.

    Use either of the following dial indicator sets with roller contact point. Special Tools and Equipment

    • J 8001 with a clamp-on base

    • J 7872 with a magnetic base

    Load the indicator and slowly rotate the assembly one complete revolution.
    Set the indicator to zero on the low spot.
    Rotate the assembly one more complete revolution and note the total amount of runout indicated. The maximum allowable assembly radial and lateral runout is 0.050 inch when measured off the vehicle and 0.060 inch when measured on the vehicle.

    Vectoring (Match Mounting)

    3.gif


    If the runout is excessive, mark the location of the high spot (3) and the low spot on the tire. Next, determine if the runout problem exists in the tire, the wheel, or a combination of both. Then, correct the problem. This procedure, called match-mounting or vectoring, uses the following steps:

    Important: After replacing a tire or a wheel, remeasure the tire/wheel assembly runout in order to verify that the runout is within tolerance.

    1. Place a mark (2) on the tire sidewall at the location of the valve stem (5). This mark is the 12 o'clock position. Always refer to the location of the high spot (3) in relation to its clock position on the wheel.
    2. Mount the tire/wheel assembly on a tire machine and break down the bead. Do not dismount the tire from the wheel at this time.
    3. Rotate the tire 180 degrees on the rim so that the valve stem reference mark (8) is now at the 6 o'clock position in relation to the valve stem (6) itself. You may need to lubricate the bead in order to easily rotate the tire on the wheel.
    4. Reinflate the tire and seat the bead properly.
    5. Mount the assembly on the tire balancer and remeasure the runout. Mark the new location of the runout high point on the tire.
    6. If runout is now within tolerance, no further steps are necessary. Balance and mount the tire on the vehicle. Refer to Balancing Tires and Wheels .
    • If the clock location of the high spot remained at or near the clock location of the original high spot (7), the wheel is the major contributor to the runout problem. Refer to Wheel Runout Measurement.

    • 4.gif


    If the high spot (7) is now at or near a position 180 degrees from the original high spot, the tire is the major contributor to the runout problem. Replace the tire.

    • If the high spot is in between the two extremes, then both the tire and the wheel are contributing to the runout. Rotate the tire an additional 90 degrees in both the clockwise and the counterclockwise directions.

    Wheel Runout Measurement
    FIGURE Lateral Wheel Runout(c)

    5.gif


    FIGURE Radial Wheel Runout(c)

    6.gif


    Complete the following steps if you cannot bring runout within tolerance by match-mounting:
    1. Dismount the tire from the wheel.
    2. Measure the radial wheel runout and the lateral wheel runout
    .

    FIGURE Radial Wheel Runout (Tire Removed)(c)

    7.gif


    FIGURE Lateral Wheel Runout (Tire Removed)(c)


    8.gif

    You can measure rim runout more accurately on the inside bead area of the wheel. Measure wheel runout using the same procedure as tire runout. Ignore any jumps or dips due to paint drips, chips, or welds.

    Measure both the inboard flange and outboard flange as shown. The tolerances for wheel runout are as follows:

    • Steel Wheels:

    - Radial runout--0.040 in

    - Lateral runout--0.045 in

    • Aluminum Wheels:

    - Radial runout--0.030 in

    - Lateral runout--0.030 in

    If the runout of the wheel is beyond the tolerance, replace the wheel.

    Important: Always measure the runout of new wheels. Do not assume that a new wheel is automatically good.

    When replacing a steel wheel, refer to the wheel code that is stamped next to the valve stem. When replacing an aluminum wheel the code is stamped on the back side of the wheel, cross-reference the letter code with the parts book.

    If the runout of the wheel is within tolerance, and the tire/wheel assembly runout cannot be reduced to an acceptable level by using the match-mounting technique, replace the tire.

    Important: Always remeasure the tire/wheel assembly runout after you replace the tire.

    If you notice a large difference in runout measurements between on-vehicle testing and off-vehicle testing, the runout problem is due to one of the following:

    • Stud circle runout

    • Hub flange runout

    • A mounting problem between the wheel and the vehicle

    The listed tolerances should serve only as a guideline. If runout measurements are within tolerance but are marginal, some sensitive vehicles may still be affected. Always reduce runout to as little as possible in order to attain optimum results under all conditions.

    Radial Force Variation

    9.jpg


    Radial force variation is the difference in the stiffness of a tire (1) as the tire rotates and contacts the road. The tire and wheel assemblies have some variation due to splices in the tire plies. These splices do not cause a problem unless the force variation is excessive. These stiff spots in the tire can deflect the tire and wheel assembly upward as the assembly contacts the road.

    If the tire has only one stiff spot, the spot will deflect the spindle once per each revolution of the tire and wheel assembly, thus causing a first-order tire/wheel vibration. If the tire has two stiff spots, the spots cause a second-order vibration. First-order and second-order tire/wheel vibrations are the most common as a result of radial force variation. Third-order, fourth-order, or higher are possible but rarely occur.

    Ensure that the tire and wheel assembly runout is at an absolute minimum. This is the most effective way to minimize the possibility of force variation as a factor in tire and wheel assembly vibrations. However, some tire and wheel assemblies exhibit vibration-causing force variation even though they are within runout and balance tolerances. These instances are becoming increasingly rare due to tighter tolerances and higher standards in manufacturing.

    If you suspect force variation as a factor in tire and wheel assembly vibration complaints, substitute one or more known good tire and wheel assemblies.

    You may buff the tires on a tire matching machine in order to eliminate spindle deflection. This type of equipment, not currently in widespread use, is designed to remove small amounts of rubber from the outer rows of the tread blocks at the location of the stiff spots under load. Do not use any tool that is designed to make the tire perfectly round. These tools will not correct the condition.

    You may substitute one or more known good tire and wheel assemblies when a tire manufacturer is not available locally.

    Lateral Force Variation

    10.gif

    Lateral force variation tends to deflect the vehicle to the side, or laterally. Lateral force variation is based on the same concept as radial force variation. A snaky belt inside the tire may be the cause of lateral force. Test the vehicle with substitute tires before installing replacement tires.

    A lateral force variation condition is rare. The best way to eliminate lateral force variation is to ensure that the lateral runout of the tire and wheel assemblies is at an absolute minimum.

    The vehicle will wobble or waddle at slow speeds of 8-40 km/h (5-25 mph) when lateral force variation is excessive. This condition is usually related to the first-order of tire and wheel rotation.

    Wheel Hub/Axle Flange Runout
    When lateral runout occurs, inspect the wheel hub/axle flange runout if you are performing an on-vehicle test procedure, but not during off-vehicle testing. The tolerances provided are only guidelines. Perform corrections only if the on-vehicle runout cannot be brought to within tolerance.




    1. Position the dial indicator on the machined surface of the hub, the axle flange, or the rotor outside of the wheel studs.
    2. Rotate the hub in order to find the low spot.
    3. Set the dial indicator to zero at the low spot.
    4. Rotate the hub again and check the total amount of runout.

    Specification (Guideline)
    Runout tolerance: 0.13 mm (0.005 in)

    Wheel Stud (Stud Circle) Runout
    Use the wheel stud runout procedure whenever the following conditions occur:

    • The off-vehicle radial runout differs significantly from the on-vehicle radial runout

    • Earlier attempts to correct the tire and wheel vibration condition have been unsuccessful




    1. Position the dial indicator in order to contact the wheel mounting studs. Measure the stud runout as close to the flange as possible.
    2. Turn the hub to register on each of the studs.
    3. Zero the dial indicator on the lowest stud.
    4. Rotate the hub again and check the total amount of runout.

    Specification (Guideline)
    Runout tolerance: 0.25 mm (.010 in)


    --------------------------------------------------------------------------------

  16. #15
    AJxtcman's Avatar
    AJxtcman is offline Cadillac Owners Connoisseur
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    Re: Vibration Diagnosis and Correction

    Wheel Hub/Axle Flange Runout
    When lateral runout occurs, inspect the wheel hub/axle flange runout if you are performing an on-vehicle test procedure, but not during off-vehicle testing. The tolerances provided are only guidelines. Perform corrections only if the on-vehicle runout cannot be brought to within tolerance.


    11.gif


    Position the dial indicator on the machined surface of the hub, the axle flange, or the rotor outside of the wheel studs.
    Rotate the hub in order to find the low spot.
    Set the dial indicator to zero at the low spot.
    Rotate the hub again and check the total amount of runout.

    Specification (Guideline)
    Runout tolerance: 0.13 mm (0.005 in)

    Wheel Stud (Stud Circle) Runout
    Use the wheel stud runout procedure whenever the following conditions occur:

    • The off-vehicle radial runout differs significantly from the on-vehicle radial runout

    • Earlier attempts to correct the tire and wheel vibration condition have been unsuccessful


    12.gif


    Position the dial indicator in order to contact the wheel mounting studs. Measure the stud runout as close to the flange as possible.
    Turn the hub to register on each of the studs.
    Zero the dial indicator on the lowest stud.
    Rotate the hub again and check the total amount of runout.

    Specification (Guideline)
    Runout tolerance: 0.25 mm (.010 in)

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