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Automotive Industry

Shake, Rattle & Roll: DIAGNOSING NVH COMPLAINTS

Motor, Jun 2006 by Warren, Mark

Squeaks, rattles and other unwelcome noises and vibrations have bedeviled techs for generations. Despair no longer! With tools and techniques designed for the purpose, many can be found and fixed.

Advances in vehicle design and construction have raised motorists' expectations and increased noise, vibration, and harshness (NVH) complaints as a result. When I first started working on cars hack in the day, customers accepted sloppy handling, rattles, poor body fit, noises, vibration and more. We were working with solid gas pedal-to-carburetor linkages, solid rubber motor mounts, solid shift linkages, solid clutch linkages, steering systems with no rubber isolation, bias-belted tires, many body penetrations, two-cylinder a/c compressors-the list goes on and on.

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Fast forward to 2006. Now we have internal engine balance shafts, viscous computer-controlled motor mounts, cable- or electronically operated shifting, electronic throttle control, rubber-mounted rack & pinion steering, mag wheels, low-profile tires, front-wheel drive, stiff bodies and frames, etc. When we get to steer-by-wire, brake-by-wire and full electric HVAC, the only body penetrations will be for wiring.

NVH diagnosis, just like driveability diagnosis, can be interesting, challenging, frustrating...and darn near impossible at times. The keys to doing it right are gethering information, observing the problem, following a logical procedure, exhibiting patience and using the proper equipment.

Gathering Information

The customer interview can make or break you on a tough NVH diagnosis. Here are the key components for success: First, the technician responsible for repair rides with the owner to duplicate and hear and/or feel the NVH problem. If a customer test drive is not going to happen for some reason-a big mistake-the service writer needs to complete an extensive interview with the customer, including a check sheet filled out by the customer.

The NVH check sheet needs to answer the classic journalistic questions of who, what, where, etc. The check sheet helps the customer describe the NVH problem (the what): Is it a clunk, clank, squeal, rattle, growl, grinding noise, etc? Also, what work has already been performed on the vehicle? While a complete repair history can reveal important information, keep in mind that customers are not always forthright about prior work done by do-it-yourselfers.

Next is the where: Where does the customer sense the NVH is coming from, where does it happen, etc? When does it occur? When turning, accelerating, braking, decelerating, driving over railroad tracks, shifting, idling, with accessories on or off, when the engine is hot or cold, etc? And finally, who: Is the problem driver-specific? Do some drivers of that vehicle not experience the NVH?

Let's cover some lessons learned from my experience. No one in the shop complex where I work (three shops) except me can hear high-frequency noise. None of the other techs there can hear air leaks in the shop, vacuum leaks, wind noise, whistles, brake or belt squeal, etc. Be honest and ask for assistance when necessary. The techs around here do.

A customer once complained of a hard thud on left-hand turns...every time. He dropped the car off and left town for three days. I drove the car every chance I got and never heard or felt anything. When the customer returned, he was angry because it appeared that we wasted all that rime and didn't repair his car. A test drive with the customer revealed a consistent hard thud every time the car was turned left in excess of 45 mph. Yeah, we were practically on two wheels-not the way I usually drive a customer's car. Further investigation revealed a broken strut mount. This was an easy diagnosis, once we had the correct information.

Another time a customer dropped off his car, complaining of a buzzing noise on acceleration. I turned off his blaring radio to try to diagnose the noise. I never duplicated the noise under any driving conditions, including turning the a/c and heater on and off. A phone call to the owner revealed no additional useful information. He returned and we drove together. Sure enough, it was a bad plug wire that was causing a buzz in his radio. Having never turned off his radio, he was unable to assist us with this critical part of the puzzle. Bottom line: Always test-drive with the customer and never fully trust the customer's information.

Visual Inspection

After all pertinent customer information is obtained, the next step is a logical visual inspection. Where to look largely depends on the complaint. For example, if the complaint is a shimmy or shake, start by checking the tires and rims. Are the tires properly inflated? Are they all the same brand? Do they exhibit unusual wear patterns? Do the tires or rims show signs of damage or curb-bashing? Look for witness marks, too. For example, is there a shadow from a missing wheel weight? Be thorough and logical in your visual inspection.

A customer with an old VW bug once called stating that she just got new tires and her car had a huge vibration. The tire shop rechecked its work and determined that the tires were balanced correctly and the new tires were fine. A visual inspection revealed one tire with 2 lbs. of weight on one side! With the bug in the air we determined the wheel had about ½ in. of runout. The customer admitted she hit a curb a few months back and probably bent the wheel then. A call back to the tire store revealed the tire guy thought 2 lbs. of weight was a lot, but that's what the machine' said to do. Remember, you can't balance bent.

Automotive Industry

Shake, Rattle & Roll: DIAGNOSING NVH COMPLAINTS

Motor, Jun 2006 by Warren, Mark

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