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Defeating Noise, Vibration & Harshness
Noise, vibrations and harshness (NVH) issues can drive your customers crazy and can be difficult to detect as you try to find the cause of such problems. NVH issues encompass a wide range of problems that include water leaks, buzz, squeaks and rattles (BSR’s), wind noise. Let’s take a look at these and other NVH issues and how to address them if, over time, they show up in a vehicle.
Wind noise is the result of air leaks. Air leaks are caused by poor sealing, improper component alignment, body seam porosity, or missing plugs in the engine compartment or door hinge pillar areas. All body sealing points should be airtight in normal driving conditions. Misalignment of body components can result from an accident and improper repair of the damage.
At times, side glass and door seals will allow wind noise to be noticed in the passenger compartment during high cross winds. This is normal. Do not try to overcompensate door or glass adjustments to eliminate cross wind noise. These actions can cause premature seal wear and excessive closing or latching effort.
Road test the vehicle to determine the location of the wind noise. Apply a piece of masking tape about 2 inches wide and 6 inches long along weatherstrips, weld seams, door seams or a molding (see Figure 1). Drive the vehicle, if the wind noise is eliminated, you found the source of the air leak. If not, move the tape to another location and repeat the road test until the air leak is found. Repair the site, as required.
Buzz, Squeaks & Rattles
Buzz, squeaks and rattles (BSR’s) can be caused by any one or more of the following conditions and can be corrected by the action indicated:
- Loose fasteners should be tightened to specifications.
- Damaged and missing clips should be replaced.
- Damaged trim panels should be replaced.
- Incorrectly installed trim panels should be reinstalled properly.
Many BSR complaints such as loose trim, can be serviced using various tapes or lubricants. Tapes including foam, flock and anti-squeak, can be used to eliminate noises caused by metal, plastic, and vinyl components. Long life lubricants and greases can also be used on a variety of components.
In Section 23-Body of the service manual for any vehicle, there is a Buzz, Squeaks and Rattles Table listing a number of products that can be used to eliminate these annoying noises. Let’s review a few of them:
- Itch and Squeak Tape—can be used on trim panels and bezels, between metal and metal, metal and plastic, metal and vinyl as well as between vinyl and plastic
- High Density Urethane Foam—can be used between metal and metal as well as metal and plastic to secure the instrument panel and to eliminate noise from heavy metal brackets; water resistant
- Nye® Grease 880—can be used on strut bushings and sway bar bushings to eliminate squeaks
Wheel Balance & Vibration
Let’s shift gears and discuss wheel balance and vibration issues. Tire and wheel imbalance, wheel runout and tire road force variation can cause vehicles to exhibit steering wheel vibration and/or seat vibration. It is more likely to see these conditions on older vehicles, but this is not always the case. Steering wheel vibration is one of those sensations that make your customer feel as if they do not have complete control of their vehicle. That can be an unsettling feeling.
Vibrations and shakes can be identified, prevented and corrected by determining the root causes of these problems. It is important to identify the root cause in order to properly diagnose the problem. Typically, a vibration in the steering wheel or the seat will be most noticeable at highway speeds (60 mph and higher). Tire pressure can have an adverse effect on ride quality. Over inflation is one cause of unnecessary vehicle shake; therefore, proper cold inflation pressure is critical to minimizing vehicle shake.
Let’s examine some other considerations to determine the cause of vibrations:
- Where is the vibration felt? Seat, steering wheel, floor pan?
- At what speed does the vibration occur? Low or high speed?
- How many miles on the vehicle? High mileage can indicate suspension wear.
- Are there any suspension components (bushings, ball joints, tie rod ends) that require replacement? This would be more likely on an older vehicle.
- When was the vibration first noticed? At time of purchase, following a specific event, such as hitting a pothole, a collision, or driving off-road?
Next, a visual inspection should be performed before road testing the vehicle or performing any repair procedure. Check for the following:
- Verify the vehicle is equipped with the correct OEM wheel and tire, as well as the presence of wheel weights (see Figure 2).
- Inspect the tires and wheels for damage, mud packing and unusual wear; correct any of these conditions, as necessary.
- Check and adjust the tire air pressure to the pressure listed on the label attached to the driver’s door opening (see Figure 3).
Figure 2 Figure 3
When road testing the vehicle, the use of a noise and vibration analyzer is recommended to diagnose the particular vibration issue. Also, if the vehicle has not been driven for an extended period of time, it is recommended that it be driven to warm the tires. This should eliminate flat spots that can cause vibration.
Road test the vehicle on a smooth road at and near the designated speed where the legal speed limits allow. Lightly place your hands at the 10 o’clock and 2 o’clock positions and observe for the following conditions:
- Steering wheel oscillation (the wheel turning clockwise/counterclockwise)
- Steering wheel high frequency movement (rapid vibration, up and down)
- Seat high frequency movement (rapid vibration, up and down)
To rule out vibrations due to the brakes or powertrain, lightly apply the brakes at the speed at which the vibration is occurring. If the vibration occurs, or is enhanced, the vibration is likely due to a brake issue. Inspect the brakes and correct any problems discovered.
Also, shift the transmission into neutral when the vibration is occurring. If the vibration is eliminated, the vibration is likely due to a powertrain issue. Refer to the differential and driveline manual for additional information.
If it is determined that the vibration is a wheel/ tire issue, re-balance each wheel/tire assembly. In addition, test for wheel runout and road force variation. This action should eliminate the wheel/ tire vibration issue. Repeat the road test to verify that the problem has been corrected.