What shape are your lug bolts and wheels in?

Among the more important parts on any truck are lugs – the bolts that keep wheels in place.

They’re hidden behind the nuts that screw onto lugs and clamp the wheels against axle hubs. While lugs are made of tough steel (or should be), they can let go without much warning – and there goes a wheel, bouncing down the highway.

That’s called a wheel-off incident, and such occurrences can and have killed people in nearby cars.

So, do you know what shape your lug bolts are in?

Lugs are among the items discussed at length during a session of ATA’s Technology & Maintenance Council meeting in September in Cleveland, Ohio. Because they’re made of steel, lugs can rust, panel members said, and because they’re under considerable tension, they can stretch and sometimes break.

There are nine other lugs securing a wheel on a heavy truck, which is comforting – there’s strength in numbers – except that some of those can fail, too. So can the wheels themselves. They can corrode, crack and deform, and the older they are the greater the possibility of failure.

First, the lugs. Being mostly hidden by nuts, the condition of lugs is not obvious but are very apparent when nuts are spun off to remove a wheel for tire work. If you do this yourself, now’s the time to look carefully at each lug. If you trust a shop to do it, try to look over the tire technician’s shoulder as he bares those bolts.

If you’re not allowed in the shop, ask that lugs be inspected along with everything else at that wheel position. A good tech in a good shop will tell you if there’s a problem.

Lugs are commonly retained during wheel and tire work, but they should be looked at carefully before remounting a wheel. Some rust is normal, but a lot of rust suggests that the lug is losing strength as the steel oxidizes and separates from the bolt.

At some point, especially when a lug appears dried out and shows some corrosion, it should get a bit of lube to protect it against rust, but not a lot because that can allow a nut to be screwed on too tightly or loosen too easily. One drop of oil is all that’s needed. Don’t bother to try to cover all the threads on the lug because spinning on the nut will distribute the lube.

Motor oil works well, because it’s a quality lubricant that will stand up to moisture, dirt and extreme temperatures.

Stretching happens after repeated use, and is caused and exacerbated by tightening the nuts too much. A stretched bolt weakens as it elongates, changing its shape. Stretching is obvious when it’s compared to a new lug.

Hold the new lug close to the old one and note any differences. If the old lug appears damaged, replace it. And look closely at the adjacent lugs, because it’s possible that they’ve been overstressed to compensate for the one that’s failed and ought to be replaced, too.

Of course, lugs and lug nuts clamp wheels to axle hubs, and those wheels also are subject to damage.

Bolt holes can be elongated if wheels move slightly against the bolts, making wheels harder to secure. And cracks and fatiguing can develop at those holes and between them. Wheels also can be weakened or damaged after repeatedly running over rough pavement or bending with tire beads when slamming through deep potholes.

Some shops will offer to repair such damage, but wheel manufacturers warn against it because high heat is usually employed to soften the metal, degrading heat-treating properties. Improper sealing of the tire bead also is possible.

During this session at TMC, representatives also said replacing the tire from that damaged wheel should be considered because materials under the rubber also could be injured.

Yes, these guys are in the business of selling wheels and tires, but they also see a lot of evidence stemming from unwise operation of components that should have been removed from service and scrapped. Safety is always the most important factor – do you want a blowout? Fixing something while it’s in the shop is much less expensive than letting it fail on the road.

By the way, when tightening lug nuts on a heavy truck’s wheel, the usual torque is 450 to 500 foot-pounds, but proper torque may vary with the type of wheel. If lug nuts must be tightened using only an impact wrench, experts recommend checking the nuts as soon as possible afterwards with a calibrated torque wrench. LL

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