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).
Photo 1: There are a lot of potential contact points here.
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.
HEARING
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.
Photo 2: When adding aftermarket parts to the mix, make sure that new problems aren’t created.
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.
SEEING
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.
Photo 3: Watch for movement that might cause contact or excessive travel in the suspension.
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.
Photo 4: Make sure all components are installed properly when dealing with aftermarket products to prevent causing problems.
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.
Photo 5: On early models, driveshaft failures were common, but the later models can still have driveshaft concerns.
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.
Photo 6: Sway bar links with ball ends can seize if the boots tear.
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.
TOUCH
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.
Photo 7: Though sway bar bushings sometimes are the source of noise, cleaning and lubricating can hurt or help.
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.
FINISHING UP
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.
More Articles in Chassis (Suspension/Steering)