Ensure your classic car’s ball joints are dependable

This article wraps up our series on The Big Six things likely to cause a vintage car to die and leave you in the lurch (ignition system, fuel delivery system, cooling system, charging system, belts, and ball joints). Today, we talk about the list’s final item—ball joints.

It may seem that ball joints are the-player-to-be-named-later of The Big Six, and in some ways, they are. If you attend a vintage car event and poll the attendees on what problems they had on the drive down, you’re likely to get many responses in the first five, and none in the last. So why put ball joints on the list at all? Why not regard them as the kind of act-of-god event like a stub axle shearing off causing you to lose a wheel?

Because ball joint failure does happen, and fairly often, on a whole range of cars. Google it, and what you see are photos of not 1974 TVR 2500s, but late-model passenger cars, trucks, and SUVs, with a front wheel folded under like that skier’s ankle in that classic ABC Wide World of Sports “the agony of defeat” video. When it happens, you lose control of the car.

Ball joints were first used in the 1950s when independent front suspensions utilizing either MacPherson struts or double wishbones began replacing the older kingpin design. MacPherson struts are by far the more common of the two designs. The strut holds the shock-absorbing cartridge, and on top of the strut sits the spring, both of which allow vertical motion of the suspension thereby absorbing shock over bumps.

A standard MacPherson strut, with the spring at the top and the ball joint and lower control arm at the bottom, on a 1972 BMW 2002tii.

But at the bottom of the strut sits the ball joint. Connected to the lower control arm, the ball joint’s ball-in-socket design not only accommodates changes in camber as the strut goes up and down over bumps, but also allows the strut to rotate as the car is steered.

The ball joint is between the bottom of the strut and the lower control arm.

What this means is that, after the flex in the tires’ sidewall, the ball joint is the first component to feel the pounding from a pothole. The strut and spring prevent the shock of impact from being transmitted to the body of the car, but the ball joint feels it with full force. And, because of the ball joint’s location at the nexus of the suspension and the steering, if it fails, you lose control of the car. There are other ball-in-socket steering components—tie rods, for example—whose failure will also cause catastrophic steering loss, but they’re not on the front line of pounding like the ball joints, and thus their failure is rarer.

On my beloved vintage BMWs, the original ball joints are riveted in. Replacement ball joints use bolts. So if I buy a car and see riveted ball joints, I know that they’re original to the car. I used to prophylactically replace these in the same way I’d replace a likely-original water pump or fuel pump before a long road trip. I’m now a little more circumspect about ripping out original ball joints, as ball joint failure occurs because the rubber boot has ripped and allowed dirt and moisture to get in.

A failing ball joint usually announces itself with a good deal of metallic thunking over bumps. If you hear anything remotely like that, evaluate it immediately, as catastrophic failure not only will make you lose steering control, but is also likely to damage the fender on the wheel where it occurs (that is, if your own safety isn’t enough motivation, think of your car!).

So here’s what I recommend.

Be certain the rubber boots aren’t ripped. In the 1950s and ‘60s, most ball joints and other suspension components had Zerk grease fittings that allowed them to be lubricated at regular intervals. This was great, as pushing in fresh lube pushed out dirt and moisture. “Lube jobs,” however, went away by the 1970s, and most ball joints became sealed units with lifetime lubrication. The problem is that, if the rubber boot tears, moisture and dirt get in and contaminate the lubricant, eventually causing the ball joint to fail. So, carefully inspect the ball joint’s rubber boot. If the boot is torn, replace the ball joint.

Be certain that the ball joint’s rubber boot isn’t ripped.

Check for play. Even if the rubber boots are intact, it is a good idea to directly check for play in the ball joints. Jack the front of the car up so the weight is off the ball joints, then support the car on jack stands. Take a pair of very large slip-joint pliers (or, as we call them in the garage, “the BFPs”), position them at the bottom of the ball joint and at any fixed point on the strut above them, squeeze them, and feel for play. If you feel any, replace the ball joint.

Some how-to guides advise using a pry bar between the control arm and the bottom of the strut. If you do this, be very careful not to rip the rubber boot. In addition, note that the pry bar is separating, not compressing, the ball joint. This isn’t the best way to test for play, since, with the wheels in the air, the weight will be off the joint, so any play is more likely to be experienced by compressing the ball joint. This is why the BFP method is generally better.

Use a big set of slip-joint pliers to directly check for play in the ball joint.

Other sites recommend grabbing the wheel and tire at 6:00 and 12:00 and rocking it back and forth to try to get the bottom of the strut to move relative to the lower control arm. You can try this, but you really need to put your back into it to create enough movement in the ball joint that you’d notice it; the BFP method is more direct.

Lastly, some DIY guides advise that to check for ball joint play, with the car on the ground and the key turned to unlock the steering, you should rock the steering wheel back and forth and listen for thunking and clunking. That’s a great method for unearthing play in the tie rods and the steering rack or box, but since the MacPherson struts are rotating around the ball joints, doing this is unlikely to isolate ball joint play. The BFP method is really the best one.

So that’s it for The Big Six. Make sure your ignition points aren’t about to close up, your fuel pump and lines aren’t ancient or leaking, your cooling system is ready for summer’s heat, your alternator is charging your battery at 13.2 to 14.2 volts, your belts are in good shape, and your ball joints are play-free with unripped boots. Now, go hit the road in that gorgeous classic car of yours!

(Next week, we start a new series on how electricity work in a car, and how to use a multimeter to diagnose common problems.)

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.