How to get rid of clunks and rattles, part 1: The first layer

The oft-stated dictum in buying a vintage car is, “Condition, condition, condition.” To most people, that means dent-free exterior, shiny paint, rust-free body, and clean, intact, rip-free interior. Those things are all important, of course, but if you’re actually going to drive your prize, what you really want is a tight car, and that has very little to do with what you can see with your eyes.

In fact, the act of making a car pretty and shiny can easily introduce rattles, thunks, and clunks. I know because this is exactly what happened to my 1973 BMW 3.0CSi. The guy who painted it 30 years ago was very good at the painting part, but not so good at the assembly part. I’ve spent much of the past 30 years de-clunking and de-rattling the car. Below are my hard-earned tips.

Clunks, thunks, and rattles aren’t the same

You might think that the distinction between clunks, thunks, and rattles is merely a choice of words, but I maintain that they are fundamentally different. Clunks are sounds that occur over potholes or rough pavement and are caused by objects—usually metal —that are hitting one another (but shouldn’t). They typically have a distinctly metallic sound and require some amount of force to reproduce. Thunks are similar to clunks, but generally they don’t make a ringy, metal-on-metal sound. Instead, the sound is deeper. And rattles are caused by small, light things tapping or rubbing with some characteristic frequency on a fairly smooth surface. They typically have a shallow, superficial sound and require very little force to reproduce.

To be clear, I’m excluding from this discussion things that are simply broken. The two biggest clunks I’ve ever had were: First, when the bolts loosened up on one of the half-axles of a Vanagon I was driving, and second, when the mounting ear of an engine mount of a BMW 2002 broke off. Those were not “this noise is driving me nuts” issues. Those were broken parts that needed to be repaired immediately.

Peeling the onion

While rattles, thunks, and clunks can come from absolutely anywhere, I do have something of a procedure, or at least a sequence, to try to track them down.

They’re like an onion that you need to peel one layer at a time. You have to locate and fix them as you find them, even if the exact one you find isn’t what’s been driving you crazy. That’s the only way to rule sounds out; as you fix problems, other noise contributors will make themselves known.

Junk in the trunk?

Don’t laugh. The first thing to do when encountering a clunky car is to completely—and I mean completely—empty out the trunk. Take out the panels covering the spare and gas tank, and then take out the spare. Why? Two reasons. First, the spare tire or panel might be unsecured. Second, you may find there’s a fire extinguisher, jack, or can of Fix-O-Flat rattling around back there. If a car makes so much noise that it sounds like there’s a box of loose tools in the trunk, there may be, in fact, a box of loose tools in the trunk. Hey, I’ve literally found loose ratchet handles and sockets banging around in the spare tire well. Go for the low-hanging fruit first.

Seats

Next, check the front seats by grabbing them at the base and sliding them back and forth, and grabbing them at the headrest and rocking them fore and aft. The seat rails and reclining mechanisms on seats in vintage cars are notoriously sloppy. I’ve applied tension in one direction with a bungee cord or even removed them entirely and driven while sitting on a milk crate to take them out of the picture and see if they were the source of what I was hearing.

Exhaust

Unless you own a rear-engine car, the exhaust is typically suspended before and after the muffler by rubber hangers. When these wear out, the exhaust bangs around. With the engine cold (so you don’t burn yourself), grab the tailpipe and shove it up, down, left, and right to check for play. In addition, it’s not uncommon for the U-bolt holding the headpipe to the transmission to loosen up. If it does, it can make one hell of a steely-ringing ruckus at certain engine speeds. Jacking up the car and physically examining the whole exhaust can be illuminating. Sometimes the exhaust is clunking because it was misaligned when installed and a portion of it is hitting the underside of the car.

Worn ball-in-socket components, bad bushings

Having plucked the low-hanging fruit (trunk, exhaust, and seats), you need to do some real work. Before I delve into clunks and thunks from the suspension and steering, let me offer a few general observations.

Previously, I wrote that clunks are usually caused by metal things hitting other metal things. If we exclude broken components, often the culprit is either a ball-in-socket component (ball joint, tie rod, or certain kinds of sway bar end links) or a bushing—a thimble-shaped rubber piece, usually with a metal sleeve through the middle, that sits inside of a metal piece and has another metal piece going through the sleeve in the center.

When a ball-in-socket component wears, play sets in and the metal can slap against the other metal and generate an honest-to-goodness clunk. In contrast, a rubber bushing is designed specifically to separate two pieces of metal. As it wears out and moves, it may generate a thunk, but it has to wear out pretty dramatically in order to have metal hitting metal. Thus, in my humble opinion, a ball-in-socket component is more likely to be the source of a metallic-sounding clunk than a bushing. Remember that when you look for clunks in the steering and suspension.

Suspension

When you think of everything that your suspension does (struts in front, shock in back, springs at all four corners, and sway bars connecting left to right), it’s a wonder that it doesn’t clunk. If the car makes loud clunking noises over bumps or potholes, and the exhaust checks out, the suspension is a likely suspect.

The tried-and-true technique for suspension testing is to go to all four corners of the car and “bounce-test” it by pushing down sharply on the body. The idea is that that corner should move, then rebound, but not continue to bounce up and down. If it doesn’t move, the shock or strut is seized. If it moves but doesn’t rebound, it’s sticking. If it continues to bounce up and down, the shock or strut is blown.

However, there are a few problems with this test. The first is, on cars with stiff shocks and springs, the bounce test simply doesn’t work, as you often can’t budge the car. The second is, seized or blown shocks will certainly affect ride quality, but they may not, in fact, be the source of an audible clunk.

The other thing is that, from a suspension thunk-and-clunk standpoint, the bounce test is less definitive than you might think. Even on cars without molar-rattling suspensions, it’s often challenging to get sufficient motion to replicate a clunk you hear while driving on rough roads. Vintage cars often have thin body panels, and care must be taken when pressing down on them to bounce it. As much as I hate the bridge-abutment bumpers on my ’74 and later BMWs, they provide a secure surface to bounce the car. I’ll sometimes stand on the big bumpers in order to get a motion going. I’d never try that with the small, lithe bumpers on earlier cars.

But even bouncing up and down on a stout bumper often still isn’t definitive for thunk-and-clunk generation. If a rear upper shock mount is worn out or detached, or if the shock itself is worn out to the point of being broken, the bounce test may cause it to announce itself, but if the problem is that the rubber at the bottom of the front spring perches is worn out and the spring is banging against the perch, or the upper strut mount is going bad, often you can’t bounce the car enough to simulate the road motion necessary to tickle this.

Another thing to check is the collar nut that holds the front strut cartridge in its tube (if your car has that design). If the collar nut is loose, you’ll hear sharp banging in the front when going over bumps. This is rarely caused by an original nut simply loosening over time, but can be caused by a recently-installed nut being inadequately tightened when the struts were replaced. You can usually reach in between the spring coils with a large pair of slip-joint pliers and tighten it.

In checking the suspension, don’t forget the sway bars. They’re typically clamped onto the front and rear subframes, with a rubber or urethane bushing between the bar and the clamp. The ends of vintage sway bars typically have holes through which long bolts pass, holding them to the trailing arms, with rubber or urethane bushings interposed. In both cases, if the bushings completely wear out, you get metal-on-metal contact. On more modern cars, the sway bar ends typically have “end links,” which are small ball-and-socket components that attach to the trailing arms. It’s very common for these end links to wear out and clunk over bumps. (Remember what I said earlier about ball-in-socket components being more likely to bang than bushings?)

Steering

A car’s steering typically offers several components that can thunk and clunk. In particular, the ball joints sit at the bottom of the front struts, at the nexus between the steering and suspension. They’re at the front line of pounding. You can’t test them by bouncing the car. Instead, you need to jack the car up and squeeze the ball joints with a large set of slip-joint pliers. If there’s any vertical play, or if the boots are ripped, replace them. This is not to save you from the annoyance of the clunking—it’s to save your life. If a ball joint fails, you lose control of the car. Take it very seriously.

Worn-out tie rods and, if the car has them, center track rods and idler arm bushings, can all contribute to clunking as well. The bearings in the mounts at the top of the shock towers can wear out and have increased play, but this usually isn’t as loud or as deep a clunk as the previous items, as it is dampened by the struts.

Subframe and trailing arm bushings

When people talk on forums about wanting a tight car, someone will often say, “Replace the bushings.” I find it a largely meaningless statement, as a car may have dozens of bushings in it. They often mean “the subframe bushings,” but those are not always a high-probability clunk source. Also, the idea that a rattle-bucket old car can be turned into a tight quiet one by replacing four bushings is simply laughable. Always remember the onion.

For example, in a vintage BMW, at the front-most extensions of the front subframe, there are two large radius rod bushings, each about half the length of a can of tomato paste. If these are worn, they may affect the crispness of turn-in, but they likely have little to do with clunks or even thunks. There are rear subframe bushings that attach the rear subframe to the unibody of the car. These can cause thunks or clunks if they’re so worn out that they’re no longer securely holding the subframe against the body of the car.

There are also typically a myriad of bushings in the front and rear trailing arms. In the front, as they wear they’ll typically cause vague and quirky steering response. They can generate thunks if they’re worn out, but the car would be actively hazardous to drive if they were so worn that they generated a metal-on-metal clunk. With that said, anything’s possible with a 40- or a 50-year-old car.

Another word about bushings. There’s been a trend to replace the rubber bushings in things like control arms and sway bars with urethane bushings, the idea being that urethane is harder and lasts longer. You can read on forums and make up your own mind, but be careful. At a minimum, urethane’s increased hardness often transmits more vibration and changes the feel of the car. In addition, I can tell you from experience that the urethane sway bar bushings on my vintage BMWs begin to squeak like old bedsprings if they’re not lubricated every few years.

Drivetrain mounts

The engine and transmission are supported by rubber mounts, and the rear differential is typically hung from them. It is more common for worn-out drivetrain mounts to cause excessive engine motion or clunks on hard acceleration than driving over rough pavement, but they should certainly be checked. Engine and transmission mounts are particularly susceptible to degradation due to leakage of engine oil and transmission fluid.

Next week: Hoods, doors, and rattles.

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Rob Siegel has been writing the column The Hack Mechanic™ for BMW CCA Roundel Magazine for 30 years. His new book, Ran When Parked: How I Road-Tripped a Decade-Dead BMW 2002tii a Thousand Miles Back Home, and How You Can, Too, is available here on Amazon. In addition, he is the author of Memoirs of a Hack Mechanic and The Hack Mechanic™ Guide to European Automotive Electrical Systems. Both are available from Bentley Publishers and Amazon. Or you can order personally inscribed copies through Rob’s website: www.robsiegel.com.