Suspension NVH Diagnosis
SUSPENSION NVH DIAGNOSIS
Suspension NVH Diagnostic Procedure
1. Customer Interview
It is important to interview the customer. Customer feedback can supply information that could be helpful in diagnosing the concern. Ask questions like:
- When is the concern present (at idle or while driving)?
- Where does the concern appear to be coming from?
- How long has the concern been there? Has it steadily become worse?
- When did the concern start?
- Does the concern change with engine speed or with vehicle speed?
- Use the customer concern evaluation sheet form shown following this procedure to record customer concern.
2. Duplicate the Noise Concern
Is the noise heard while bouncing the bumper of the vehicle, driving over rough road surfaces, braking, when driving, or while parked?
Typically, front underbody noise is heard while doing the static bounce test (bouncing the bumper or the vehicle). If the noise can not be duplicated with the static bounce test, or during low speed turning maneuvers, it is most likely not suspension related.
3. Isolate the Noise Concern
If the noise can be duplicated by the static bounce test, one of the following methods will help to locate the problem while doing the static bounce test.
- Use Chassis Ear (SST 107-R2100) to determine the area of the chassis that the noise appears to be coming from.
- Place your hand on the coil spring, radius arm, or stabilizer bar. This method is sometimes misleading as the vibrations may carry from one suspension component to another.
4. Inspecting the vehicle
While inspecting the vehicle in the general area of the source of the noise, look for the following:
- Loose fasteners
- Worn/broken parts
- Excessive dirt/rust accumulation
- Signs of leaking fluid
- Debris wrapped around the driveshaft, halfshaft or axle
5. Repair of the vehicle
Use the symptom troubleshooting chart to find which diagnostic test, actions or other section(s) to see.
6. Test drive the vehicle
Repeat the method used to duplicate the problem to verify that the noise has been repaired.
7. Follow up with the customer
Follow up with the customer according to the Mazda After Service Follow-up Guide to ensure that the noise was correctly identified and repaired.
Customer Concern Evaluation Sheet
NOTE:Make copies of this page and provide them to service advisor personnel.
Suspension NVH Road Test Procedure
Noise, vibration and harshness (NVH) diagnosis must start with the customer interview and be followed by a road test.
NVH usually occurs in five areas:
- Tires
- Engine accessories
- Suspension
- Drivetrain
- Body and interior trim panels
NOTE:A gear-driven unit will produce a certain amount of noise. Some noise audible at certain speeds or under various driving conditions is acceptable. Slight noise is not detrimental and must be considered normal.It is important that an NVH concern be isolated into its specific area as soon as possible. The easiest and quickest way to do this is to perform a road test.
NVH Diagnostic Locator
Road Test
NOTE:Do not make adjustments until a road test and a thorough visual inspection of the vehicle is performed. Do not change the tire pressure or the vehicle load. This may reduce the condition's intensity to a point at which it cannot be identified clearly. It may also inject a new condition into the concern, preventing proper diagnosis.
1. Use the Vehicle Road Test Evaluation (form shown following the last step of this procedure). Make notes on the backside of the form throughout the diagnostic routine. Make a visual inspection as part of the preliminary diagnostic routine, writing down anything that does not look right. Note the tire pressures, but do not adjust them yet. Note leaking fluids, loose nuts/bolts, or bright spots where components are rubbing against each other. Check the cargo area for unusual loads.
2. Perform the NEUTRAL engine run-up (NERU) test. It identifies engine or exhaust-related vibrations and helps in sorting out vibrations that are found in the road test.
1 If the vehicle is equipped with a tachometer, it can be used. Otherwise, a tach must be connected.
2 Locate the vehicle away from other vehicles and walls which may reflect sound differently than a road.
3 Put the vehicle in NEUTRAL or PARK and do not set the parking brake or press on the service brake since these are not engaged in a road test.
4 Run the engine rpm up from an idle to approximately 4,000 rpm and note any moans, vibrations, noises, etc., and the rpm at which they occur. Sometimes it is possible to "tune in" on these conditions by running the rpm up and down to determine a precise rpm at which they occur; in other cases they will fall over a broad range of rpm. This establishes a baseline against which driving vibrations can be measured.
5 If you suspect that the exhaust system is vibrating, hang a ring of keys or something similar from the tailpipe and listen for the rattling of the keys as the engine is run up and down.
6 When conducting the road test, see the results of the NERU test to distinguish vibrations and noises caused by the engine from those caused by the transmission, the propeller shaft, or the axle. If a vibration or noise occurs at a particular speed, try operating in another gear at the same speed. This changes the engine rpm and helps to distinguish engine induced vibrations and noises. If it occurs at a particular rpm, use different gears to test at the same rpm at different road speeds.
3. Perform the drive engine run-up (DERU) test.
WARNING:Set both the parking brake and service brake and make sure to perform the test with enough space ahead of the vehicle to eliminate the possibility of an accident should the vehicle unintentionally lurch forward. Failure to follow these instructions may result in personal injury.
CAUTION:Do not conduct this test for over 30 seconds, or without periodic driving or shifting to neutral to circulate transmission lubricant; otherwise the transmission will overheat causing severe damage to the automatic transmission.
4. Run the engine rpm up and down between an idle and approximately 2,000 rpm with the transmission in DRIVE. Note the nature of any vibrations and noises and when these concerns occur in relation to engine rpm.
5.
NOTE:The type of road and its surface condition are important factors in the road test. A smooth asphalt road that allows driving over a range of speeds is best. The brushed concrete road surface found on many expressways and the coarse aggregate sometimes found in concrete can mask many vehicle noises and make NVH diagnosis difficult.Road test the vehicle and define the condition by reproducing it several times during the road test.
1 A tachometer must be used.
2 Note the fuel level. Some vehicles change in their response when the fuel level changes.
3 Try to duplicate the conditions with the customer present, particularly the speed and throttle operation.
4 Find the speed where the concern is most severe.
5 Accelerate gently through this speed to a few mph above it and then coast back down a few mph below it and note if the concern changes.
6 Repeat this procedure, if necessary, to get a feeling for the behavior. Then drive about five mph above the speed, put the transmission in NEUTRAL, and coast down. Note any change in behavior.
7 Try "floating" the driveline by backing off slightly on the throttle at the speed at which the condition occurs. The idea is to unload the axle gears and the universal joints as much as possible. If the concern does not change in all these modes of operation, the cause may be driveline imbalance since the imbalance is not changed by the throttle position.
6. Perform the road test quick checks as soon as the condition is reproduced. This will identify the proper method of diagnosis. Run through the quick checks more than once to make sure you are getting a usable result.
Road Test Evaluation Sheet
Road Test Quick Checks
1. 24-80 km/h (15-50 mph): With light acceleration, a moaning noise is heard and possibly a vibration is felt in the floorpan. It is usually worse at a particular engine speed and at a particular throttle setting during acceleration at that speed. It may also produce a moaning sound, depending on what component is causing it. See Symptom Troubleshooting Chart - Suspension NVH.
2. 40-72 km/h (25-45 mph): With steady to heavy acceleration or deceleration, a rumble-type noise is heard. It is very intense during heavy acceleration or deceleration and very light during cruise or neutral coast. The vibration is hard to duplicate with vehicle supported on a hoist, since the wheels are coasting free. For propeller shaft vibration diagnosis, see Symptom Troubleshooting Chart - Suspension NVH.
3. High Speed: With slow acceleration and deceleration or at constant speed, a shake is sometimes noticed in the steering wheel/column, seats, floorpan, trim panels or front end sheet metal. It is a low frequency vibration (around 9-15 cycles per second). It may increase when applying the brakes lightly. For high speed shake diagnosis, see Symptom Troubleshooting Chart - Suspension NVH.
4. High Speed: A vibration is felt in the floorpan or seats, with no visible shake, but with an accompanying sound or rumble, buzz, hum, drone or booming noise. It will exist in all drive modes, but may vary somewhat in acceleration, deceleration, float or coast modes. In some cases, the driveline vibration is eliminated in the float mode. For Propeller Shaft Vibration diagnosis, see Symptom Troubleshooting Chart - Suspension NVH.
5. Neutral Engine Run-Up: A vibration is felt whenever the engine reaches a particular rpm either with the vehicle in motion or while the vehicle is sitting still. It can be caused by any component from the fan back to the clutch or torque converter and by anything that turns at engine speed when the vehicle is stopped. For Engine Accessory Vibration diagnosis, see Symptom Troubleshooting Chart - Suspension NVH.
6. Noise and Vibration While Turning: Clicking, popping or grinding noises may be due to the following:
- Cut or damaged CV joint boot resulting in inadequate or contaminated lube fill in the CV joint
- Loose CV joint boot clamp
- A component contacting the halfshaft assembly
- Worn, damaged or improperly installed wheel bearing
- Worn, contaminated or dry CV joint
Suspension NVH Hoist Test Procedure
WARNING:If only one drive wheel is allowed to rotate, the speed must be limited to a maximum speedometer reading of 55 km/h (34 mph) since the actual wheel speed will be twice that indicated on the speedometer. Exceeding a speed of 55 km/h (34 mph) or allowing the drive wheel to hang unsupported can result in tire disintegration/differential failure, which can cause serious personal injury/extensive vehicle damage.After a road test, it is sometimes useful to do a similar test on a hoist. (Use an axle hoist, not a frame hoist. An axle hoist will not change the driveline angles. If only a frame hoist is available, axle stands must be used.) Make sure the 4WD selector is in the 2WD mode on a 4WD vehicle.
WARNING:A vehicle equipped with a Traction-Lock(R) differential will always have both wheels driving. If only one wheel is raised off the floor and the rear axle is driven by the engine, the wheel on the floor could drive the vehicle off the stand or jack. Be sure both rear wheels are off the floor. Failure to follow these instructions may result in personal injury.
1. Elevate the rear wheels slightly. Check to make sure both wheels will turn.
2. Start the engine and shift the transmission into DRIVE. Explore the speed range of interest using the drive/cruise/float tests. See road test in.
3. A coast down in NEUTRAL must also be conducted.
- If the vehicle is free of vibration when operating at a steady indicated speed and behaves very differently in DRIVE and coast, an axle concern is likely.