By Greg McConiga
These unpleasant sounds unsettle motorists’ peace of mind, making them imagine fiery crashes. Unfortunately, relieving their psychic distress isn’t always easy. You need a plan.
Front end noises can be tricky and frustrating. In fact, we think it could be argued that steering and suspension noises are among the most difficult things we chase in the auto repair industry. Why? Because the whole front of the car is a sounding board, every part is closely coupled or attached, several of the individual components have similar natural resonant frequencies and there are a lot of parts involved when turning the wheel or stepping into or over road irregularities. It’s just damn hard to isolate which piece is talking when so many are in play.
Plus, attempting to recreate the problem is often met with little success. The angle of the curb the customer drops down over in the morning backing out of his or her drivway isn’t the same as the angle of your test curb. The car is now warm, not cold — or, now cold and not warm. You weigh more or less than the customer. You don’t drive twenty over the limit or up on two wheels. Or, any one of a hundred other variables might muddy the mix. Is there hope?
Noises are vibrations in the audible range, 20 Hertz to 20,000 Hertz for most people. The duration of the noise doesn’t matter any more than the form it takes when we detect it. Noise is noise because the air that reaches our eardrum is vibrating, which makes our eardrum vibrate sympathetically. From there on, it’s what we used to call “PFM” in the Navy — “Pure Freakin’ Magic” — and it’s well beyond my meager abilities to clearly explain the physical attribute we call “hearing.” The customer hears it, that’s the important part.
Low-pitched sounds are lower frequency, closer to the 20 Hz number and high-pitched sounds are higher frequency, closer to the 20,000 Hz number. In general, heavier parts vibrate at lower frequencies and lighter parts at higher frequencies – but not always! Try this: Hang a standard 12 in. ruler over the edge of a desk with all but the last couple of inches out in space. Now pull the end down and release it and watch the frequency of the suspended end as it bounces up and down. Now do it again, only this time pull the ruler back over the desk shortening how much hangs off the edge as it oscillates. The ruler tip will pick up speed as the length becomes shorter, and the noise it makes will become higher pitched. Less mass, higher frequency, more mass, lower frequency — do you see it? Equally important, since the source of the noise is vibration, you feel the noise as well as hear it. Hang half your ruler over the edge of the desk, pluck the end and feel the desktop as it vibrates and you’ll get what we mean. Understanding that noise and vibrations are linked is an important tool in the diagnostic box. You might be able to feel a problem if you can put your hands on the parts while someone bounces the car.
Noises are variously described as a thump, thud, rattle, click, snap, pop, squeak, squeal, groan, clunk or moan, to name just a few of the words customers use to describe their particular noise. Diagnostic tip number one: Always ride along with the person who hears the noise (not the spouse who never hears it), always let the customer point out the noise and always listen to it with your own ears. Why do this? So you will know which noise (there are often many, some of which are normal, and there’s nothing more frustrating than fixing the “wrong” noise).
You also need to recognize its acoustic signature when you hear it again and you need to know the approximate area affected. There are those who will insist that they won’t “waste time” in this manner, but where noises are concerned, the technician will always be time and money ahead by riding along to hear the noise personally. As an added benefit, if the problem is intermittent and today isn’t its day to misbehave, you’ve got the best witness in the world there to confirm that you were “unable to duplicate.”
Ride-alongs are also the perfect time to discuss past repairs or repair attempts with the customer and gather facts. Has the car ever been wrecked and repaired? Was there any event that could be linked to the start of the problem? Given the influx of low-quality off-shore parts, you need to know what has been done, when and where. Review copies of bills if prior work has been performed and check that the prices aren’t “too good to be true.” Don’t assume that new parts are good parts. McConiga’s axiom number 188: New parts are different parts. They may or may not be good parts. Inform customers ahead of the fact that you’ll need them to reserve time for a ride-along at arrival to avoid misunderstandings.
Diagnostic tip number two: Always check service bulletins. You can probably fix 85% of your problems with TSBs. There are hundreds, if not thousands, of known sources of steering and suspension sounds along with the correct fix listed in sources like Alldata, Mitchell On-Demand, Identifix-Direct hit, or the manufacturer’s tech service websites. Nearly 100% of known fixes involve updated or revised parts or materials. Reinstalling the same part that caused the problem isn’t a repair, it’s just a deferred comeback. Don’t forget sources like www.moogproblemsolver.com/library, either. The guys who make the parts know the problems they’re trying to address.
The nature of the noise is your first clue. Squeaks are usually attributable to dry metal parts in direct contact. Since the advent of Goofy Lubes, I always look at steering stops first. In fact, performing routine lubrication isn’t a bad way to eliminate the obvious. Look at ball joints and tie rod end sockets and check for canted bushings. Red dust around parts is a sign of fretting, the process of wear that produces a fine metallic dust, which then rusts and sticks around the area where the failure is occurring. Also, keep an eye out for other witness marks that might be present. Shiny areas around fasteners, disturbed paint or fresh tool marks are good places to begin your investigation.
While most manufacturers have moved away from bearing-style upper strut mounts due to high failure rates, poor steering return, memory steer and noise concerns, there are still plenty out there. They’ll squeak in turns once the water exclusion system fails and the bearing rusts.
Squealing is usually connected with rotation. Obviously, belt squeal will be likely on a car with a failing auto tensioner or power steering pump, but squealing may also occur at any seal-to-shaft interface. Any ball and socket joint in failure may also squeal in turns. Of course, brakes are notorious for creating squeals, but they’re not part of our subject here.
Knocking noises occurring on bumps, especially in turns, can be caused by anything steering-related that’s more heavily loaded on one side than on the other. The gear, mounts, inner and outer tie rod ends and steering intermediate shafts are all suspect. Intermediate shafts have introduced a whole new set of noises in the form of rotational knocking or clunking in turns. Late model cars are designed to have the powertrain tear away and exit out the bottom of the car in a hard front end hit, and also have collapsing intermediate shafts to keep the column from spearing the driver. The early fixes involved special lubrication kits, but nearly everyone is on a second or third design today. Make sure you get the latest parts.
On cars that have removeable shock units inside the struts, knocking, clunking or thumping may be due to nothing more than a loose strut gland nut.
Rattles can come from dozens of places and apparent location will be a big help in running the problem down. High up means the strut mount, a spring isolator or a broken spring. Lower down may be related to the sway bar or sway bar links. Many manufacturers have gone to low-friction links between the sway bar and control arms, sort of like miniature tire rod ends on a short link made of either plastic or steel. These are failing at a ferocious rate. Watch removal and installation of these parts because the tiny ball socket won’t tolerate being spun with air tools. Moog has a metal design with grease fittings that will fix some of these complaints permanently. Other rattlers include broken struts and brake pads moving in the caliper.
Popping or clunking during stops suggests parts that are shifting under weight transfer. Ford continues to use strut rods on some models, and if the strut rod bushings are worn, suspension components can shift under deceleration. Also, check control arm bushings and cradle mount or body mount fastener torque.
Far and away the greatest undercar noise diagnostic tool every made is the ChassisEar by Steelman. We’ve had the old reliable wired system in our toolbox for years, and we can’t begin to tell you how many cars we’ve fixed with it. As great as the wired system was, it was a pain to connect. You had to be careful about routing, making sure that everything was tied up carefully. We’ve snatched more than one transducer off the car when our carefully secured leads met something that rotates. The new wireless system is great! You can secure it using the magnets in the transmitters, but we don’t trust them unless the transmitter is lying flat. If it must be mounted on a vertical surface, we tie it down. The supplied Velcro fasteners work well, as well as nylon wire ties, rubber bands and binder clips.
Even though the tool is excellent at letting us eavesdrop on the chassis, it still relies on our ability to judge noise levels and zero in on the source by moving sensors until the noise is loudest, which is kind of subjective. A row of LED’s that light up with increasing volume helps, but it’s still not 100% cut and dried.
We made an adapter that allows us to feed the output of the ChassisEar into a lab scope. It’s a simple
1/8 in. stereo jack wired to a length of shielded cable, which is then attached to the scope leads. The acoustic signature is the waveform shape, which remains approximately the same, less any background noise bleed. The amplitude of the waveform is its level or volume. Just use the volume knob to set a base level and leave it there, and as you move your probes closer to the source the amplitude of the waveform (distance from top to bottom) gets larger and larger. Radio Shack has the parts to make this simple jumper if you’re interested.
By the way, Steelman also makes the EngineEar, which is a great companion to the ChassisEar. Its extended probe amplifies sound and has a second setting for detecting vibration. Good stuff to have when you’re chasing noise in tight spaces, or trying to figure out which pulley is making noise on a car with a compact belt plane.
Finding noises is a matter of attention to detail, determination and using the resources you have as they were intended to be used. Happy hunting!
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