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Understanding Post-Repair Sound Dampening

( 06/18/2019 ) Written by: Douglas Craig

One of the biggest consumer complaints about a vehicle post repair is that sounds “tinny” – like a tin can or an irritating, high-pitched noise – from inside. More often than not, technicians repair the fender or door but haven’t replaced noise, vibration and harshness (NVH) or beta patches or have not reattached door skins to the body structure – such as underneath a door beam.

This all affects sound dampening. Eliminating – or at least reducing – any noise or vibration does not change just how a car rides but how it actually feels. Automotive NVH materials provide either acoustic absorption or acoustic insulation to absorb sound. Noises and audible body sounds are two major grievances from vehicle owners, which contribute to how a vehicle handles and to the overall driver experience.

A tinny sound comes from not replacing NVH material removed during vehicle repair. It is absolutely critical to put back any sound dampening material originally installed by the original equipment manufacturer (OEM) during the assembly process.

During vehicle teardown, the technician should closely examine (to determine softness and stiffness) and identify what is currently installed by both looking and touching the material that needs to be replaced. This will help ensure that the repairer is able to choose the proper NVH material or replicate it as closely as possible.

Some parts and materials – such as fiberglass-reinforced epoxy patches that adhere to the inside of fenders, doors and quarter panels and are cured when the vehicle undergoes an OEM’s e-coat and curing processes – are intended to provide extra support to exterior body panels in areas that may be prone to oil canning or panels that manufacturers have identified as commonly leaned against where the load needs to be spread out. (Yes, OEMs do actually consider the user’s actions, such as leaning against a vehicle, and try to provide some protection/additional support.)

These types of patches are often, but not always, included with service parts. When they are not included, additional effort is needed to complete the repair, but some patches can be fully recreated in the field. Repairers can remove the original patch and re-adhere it with adhesive as one option. Other options include the following:

  • Using sprayable sound dampeners (Fusor HD, for example) or self-adhering products applied to the inside of the panel in question. The technician needs to determine what will be proper if the OEM guidelines do not make it clear. Replace a stiff patch with something stiff and a flexible patch with similar pliability.
  • Replacing the coatings – both inside and out – on the underbody. This is very important as it will eliminate the pinging sound created if, for example, a stone flies up and hits the floor. A minor noise heard inside the vehicle from a stone outside of it may not seem like a big deal. However, eliminating that kind of sound is more than simple noise reduction. The ping created from that same stone hitting the underbody could be picked up by various sensors and misconstrued as an issue.

For example, it could affect the vehicle’s yaw sensor. When the floor above the transmission panel in a vehicle by one particular manufacturer gets hit by a stone, it triggers a body sensor.

A miscommunicated data point from that sensor, along with all the other data from other sensors, can cause the malfunction indicator lamp (MIL) lamp to illuminate as “confusion” exists. To address the situation, the OEM issued a bulletin with its recommended NVH materials to use during vehicle repair so the “sound” is dampened should a stone bounce around and hit the underbody in the area of concern.

For tips on how to confidently choose noise, vibration and harshness materials during vehicle repair, view my article Increase Customer Satisfaction with New Technologies in Sound Dampening in ABRN.

Douglas Craig

In his structural adhesive technical service role at LORD, Doug is responsible for providing guidance and repair solutions to repairers, OEMS and insurers which incorporate the proper materials and methods. Doug's previous role, as the Collision Repair Manager at Fiat Chrysler Automobile, was focused on all topics related to collision damageability and repairability.

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