One of the more difficult aspects of automotive diagnosis and repair is finding and correcting “noises.” Though not all noises come from the suspension, most of the movement in any car that can cause noise is related to the movement of the suspension, or other parts connected to it. Of course, everything is somehow connected to the suspension and from there to the road (see Photo 1).
Most of the challenges of noise diagnosis and repair come from misunderstanding the customer’s complaint. And, as suspension systems have gotten more complex with many more points of potential failure, making thorough repairs means taking the necessary steps to get a good outcome.
Over the years, there have been many tools specifically designed to help the technician in tracking down noises. Some work better than others for various automotive systems and faults. Leak detection in door or window seals, bearing and gear train noises, or engine and powertrain noises can often benefit from the use of electronic or even mechanical noise enhancers. But, suspension noises are a different form of noise. Often intermittent, compromised by interference from other noise sources or isolated to inaccessible areas makes suspension noise diagnosis particularly difficult.
The most difficult part of the noise diagnostic process is evaluating the complaint and, more specifically, the exact noise that the customer hears. I can tell you that making a snap diagnosis without experiencing the actual noise can make customers distrustful and unwilling to bring the car back if a problem is not resolved.
As with all diagnosis and estimation of costs, accessing the relevant service manual, TSBs and pattern failures for a particular model is important. Knowing the vehicle you’re servicing, how it’s normally used and having a service history can go a long way in tracing difficult noises.
This article is not the total answer to locating specific problems on any car or model. My intent in writing this article is to get you and your team thinking about all of the tools you have available to perform accurate and successful repairs when dealing with noise complaints.
STARTING THE DIAGNOSTIC PROCESS
Since we are discussing noises, the most obvious first step is going to be using your ears. The process doesn’t start in the shop, but at the front desk. This process is the forte of a good listener — and getting to the actual complaint can only be achieved by a careful, comprehensive and focused write-up.
One problem I encountered years ago was a customer who complained of a noise that sounded like a “thumping” noise that came from the rear of the car on turns.
The noise was not there when driving straight, and didn’t seem to be related to going over rough roads. The dealership was in the city, so rough roads didn’t really enter into the equation anyway. I wrote the car up with as much information as I could gather and sent it to the technicians in th
e shop, with enough time authorized to road test and report back.
The report: nothing found! I took the car out and drove it myself, and heard the noise immediately on the first turn. I went to the trunk and found a half dozen, empty 2-liter soda bottles. Unsecured, they would roll from one side to the other side in the trunk on alternating turns. The problem was that the technician took the car around the block, making only right turns, heard the noise once and didn’t get it to repeat! I’m only relating this story because it fits with noise diagnosis. You have to think out of the normal box to trace down noises that may come and go.
Taking the time to glean as much information as you can from the customer at write-up will certainly enhance the process and repair. There will be times with difficult noises that a test ride with a customer might be necessary, or an extended road test to an area where the problem can be duplicated will be the only chance to get it right.
USING ALL THE TOOLS YOU ALREADY HAVE
The title of this article is “making sense of suspension noises,” but probably could be better said as “using your senses against suspension noise.”
We all hear things a little differently, with varying degrees of hearing capability, different decibel ranges and hearing acuity. I know that I hear noises that no other person hears (no, not that kind of noises!), and the same is true of others. That may seem strange, but years of trying to pick internal engine noises out of large and small diesel engines has taught me to listen very carefully and search through every spectrum of sound.
Once you have a good idea of the kind of noise you are looking for, and the conditions that might cause the noise to present itself, you need to focus on that noise alone.
But suspension noise, as I noted earlier, isn’t just about hearing the noise. Your other senses come into play too; you just need to use them. Sight, touch and hearing can all be used individually and together to locate and resolve a suspension noise problem.
Taking a test drive is most likely going to be necessary if the noise is truly a suspension problem. If the customer complaint doesn’t involve driving to recreate the problem, look elsewhere. Of course, there are some suspension noises that, though present when driving, can be recreated in the shop with the help of a fellow technician.
Bounce-testing the suspension might point up a likely source. Don’t forget, however, that suspension movement on the road involves upward as well as downward suspension travel (see Photo 2). Particularly with shock or strut noises, unloading the suspension might be the reason for a clunk or rattle.
Movement of the car side-to-side can also encourage suspension movement and noise creation. Setting the parking brake and moving the car forward and in reverse with the drivetrain under stress can also induce suspension movement and noise. Being able to create a specific noise in the shop should make pinpointing the source easier and more reliable. For noises that aren’t real specific, getting the customer to acknowledge that a particular sound is the correct one is a good practice before doing extensive repairs or parts replacement.
If a suspension noise seems to be related to braking, acceleration or turning, a lot can be learned by observation of the vehicle, even in the parking lot. Obviously this will involve two people, one driving and the other observing. Looking carefully at how the suspension and body interact during actual driving maneuvers can often point out a problem that otherwise isn’t apparent.
Especially on 5 and 7 Series BMWs, the thrust arms, ball joints and control arms can move under changing attitudes that don’t produce driving problems, but show up as excessive movement (see Photo 3) and, in many cases, as noise. One such method is to drive past an observer at a low speed while applying the brakes.
Rearward movement of the wheel in the wheelwell (front or rear) can help locate where there may be a deflection issue that causes an interference problem between the suspension movement and body or other components. There will always be some deflection, depending on the speeds involved, but by comparing movement from side-to-side, it will be obvious when the movement is abnormal.
Particularly on cars with aftermarket parts, interference problems may not be readily apparent (see Photo 4) until there are wear or contact points that cause damage over time. Doing this same procedure in reverse can point out problems that might only be noticeable when backing. Though aftermarket suspension components are very often more compact than OE, the addition of oversize wheels and tires can still cause interference, or load the suspension enough to cause contact.
On difficult noise problems, a thorough inspection front to rear might be needed to see a problem. Look carefully for differences between the components on one side of the car, from the same components on the other side. Don’t forget to look at non-suspension parts as well. Plastic covers on the bottom of the car, when loose, can make noises similar to suspension noise. Driveshaft noises, especially on earlier models, can also be a source that might not be obvious (see Photo 5). Any indication of a rear-end collision should always be a consideration for possible driveshaft noise or vibration.
One potential marker for a noise generator is a rusty area around fasteners. A suspension or body mount that is loose will very often cause a rusty residue to form between the mount and the retainer or component. I usually have a ratchet with several common sockets available during an inspection, just to be able to quickly check for something that might be loose. All fasteners have torque specifications, so if you do find something loose, get out your torque wrench and tighten it correctly. Over-tightening a suspension fastener can cause a catastrophic failure if it breaks.
Look for deformed, torn or cracked suspension insulators, mounts or sealing boots for joints. On BMW models, the front sway bar links with ball ends (see Photo 6) have a tendency to seize with a torn boot and are usually the reason for the failure.
One other item to look for is contact between components. These are often easy to spot when there has been contact over a period of time that causes the paint to be gone. There may also be a rust stain at contact points, if the noise is a bit more than intermittent.
There are those really annoying squeaks, clunks and rattles that happen when going over a speed bump, or when turning in a parking lot, that tend to drive customers nuts. Often, these noises are the hardest to find, many are hard to duplicate and may need to be duplicated under very specific circumstances.
For pinpointing a noise like this, where you can hear it but can’t see anything obvious, there may be a need to get down on your knees. Not to pray, even though that might seem to help sometimes, but to actually put your finger on the problem.
What I’m talking about is having a helper move the vehicle (engine off, nobody in the driver’s seat, parking brake on or car in park at least) while you lay on your back gently touching suspension components. Any feeling of roughness or uneven movement might lead to a defective part that fails under the weight of the car.
Sway bar bushings (see Photo 7) are the prime offenders most technicians look at first. I see so many cars with continuing noise complaints where the sway bar bushings have been sprayed, gooped or replaced with a different type in an attempt to resolve a noise complaint, that I have pretty much given up on trying to always go there for a noise problem.
The fact is, most manufacturers have spent years and many dollars in perfecting the materials, placement and properties of their sway bars and mountings to address this problem. It could be a problem, but usually not, and except in a very few instances, lubricating sway bar bushings often destroys the bushing and just adds another source of noise. Look instead at the mountings and links first as noted above.
If you just have to spray something on bushings, do not use any product with a petroleum or solvent-based propellant. Anything goopy is just going to attract dirt and make things worse. The best way to resolve sway bar noise is to disassemble the mountings, clean everything and either apply some Teflon tape to the bar, or use a small amount of silicone type lube.
This article isn’t going to completely resolve any noise complaints on a BMW or any other car that might be in your shop. My point is that you have to spend the necessary time, with the right tools, to accurately locate, verify and repair suspension noise complaints.
You already have a lot of the tools needed for this, now just call the customer and learn first-hand the real noise they’re hearing.
Oh, and if you smell something burning, like oil leaking onto the exhaust, collecting on the bottom of the car, maybe there is a way to smell your way to a solution for a suspension problem!
Taste, on the other hand…I’m not going to go there.