The truck will not hold a lane. Tires, steering, suspension or something else?

Wandering, pulling and play are different complaints

Wandering is a truck that will not hold a straight line on its own. You find yourself constantly making small corrections, the truck drifts one way and then the other, and it feels vague around center. Pulling is a steady tug toward one side that you have to hold against, all the time or only in certain conditions such as braking or acceleration. Excess play, or lash, is free movement in the steering wheel before the front wheels respond: you can turn the wheel some distance without the truck changing direction at all.

The three often travel together, since worn steering parts create play and play makes a truck wander. But a truck can pull hard with no play at all, or wander with a tight steering system if the tires or suspension are the problem.

The usual causes, most likely first

Most steering complaints trace back to one of these.

• Tire pressure or wear that does not match. A steer tire running lower than its partner on the other side creates more drag on that side and pulls the truck toward it. Steer tires with different tread depths, different tread patterns or different brands can do the same. A low or flat tire in a set of duals changes how the drive axle tracks, too. Our post on semi truck tire sizes covers why matched tires matter.
• Worn steering components. Tie rod ends, drag link ends, the steering shaft's universal joints and the steering gear all wear. Every bit of wear adds free movement and lets the front wheels steer themselves on bumps and grooves.
• Loose U-bolts or a broken spring. On leaf-spring suspensions, U-bolts clamp the axle to the springs. If they loosen, or a spring leaf breaks, the axle can shift out of position, and a drive axle that is no longer square to the frame steers the truck from behind.
• Air suspension at the wrong height. A leaking air bag or a faulty height-control valve can leave one side of the truck lower than the other. That changes the angles in the suspension and driveline and can make the truck lean, wander or pull.
• A brake pulling on one side. If the truck pulls only when you brake, suspect one steer brake doing more or less than the other: an out-of-adjustment slack adjuster, a weak or failed brake chamber, or brake linings contaminated with oil or grease.
• Alignment. Toe, camber and caster settings, and the squareness of the drive axles to the frame, all decide whether the truck tracks straight. Alignment can be knocked out by a pothole or a curb strike, or drift out as parts wear. Tires wearing unevenly across the tread are often the first clue.
• Load and crosswinds. A load that is heavier on one side can make a truck pull, and a light or empty high-sided trailer in a crosswind can push the whole combination around. That is not a mechanical fault, but it feels like one.

What the federal rules say about steering play

Excess steering lash is not just uncomfortable. 49 CFR 393.209 sets maximum steering wheel lash for commercial motor vehicles, measured at the rim of the steering wheel, and the limit depends on the diameter of the wheel and on whether the truck has manual or power steering. For power steering, which is what most trucks have, the table allows up to these amounts of free movement.

• 18-inch steering wheel. Up to 4¾ inches of lash with power steering, or 2¼ inches with manual steering.
• 20-inch steering wheel. Up to 5¼ inches with power steering, or 2½ inches with manual steering.
• 22-inch steering wheel. Up to 5¾ inches with power steering, or 2¾ inches with manual steering.
• Other sizes. The rule also lists 16, 19 and 21-inch wheels, and for sizes not in the table it sets a limit of 30 degrees of steering wheel rotation for power steering and 14 degrees for manual steering.
• The rest of the system. The same section requires the steering column to be securely fastened, bans worn or welded universal joints, requires steering gear boxes to be free of loose bolts and cracks, requires the pitman arm to be tight, and requires power steering to work properly with no leaks, frayed belts or low fluid.

The suspension side of the rules

Steering and suspension problems overlap, and so do the rules. 49 CFR 393.207 says no axle positioning part may be cracked, broken, loose or missing, that all axles must be in proper alignment, and that no leaf spring may be cracked, broken, missing or shifted out of position. For air suspensions it requires the vehicle to stay level and limits leakage. How a particular defect is treated at a roadside inspection is a question for your carrier's safety department; our post on DOT out-of-service faults gives the general picture, but it is not legal advice.

The practical point is simpler: a truck with excess play, a broken spring or a shifted axle is less able to respond in an emergency, and should not be driven on until someone has looked at it.

What you can check without crawling under the truck

Pull off somewhere safe, set the parking brakes, and put your flashers and warning triangles out if you are on a shoulder. Then work through what can be seen from the outside.

• Tire pressures. Check both steer tires with a gauge, and look for a low tire in any set of duals. Compare against the pressures your fleet or tire maker specifies for the load.
• Tire wear. Look at the steer tires for tread worn more on one edge, feathered or scalloped wear, or mismatched tread types. Uneven wear often points to alignment or worn parts.
• Ride height. Stand back and look at the truck from the front and rear. One side sitting lower than the other, or a hiss near an air bag, points to the air suspension. Our post on a blown air bag or dumped suspension covers that fault.
• Obvious damage. From beside the truck, look for a spring leaf hanging out of place, an axle visibly out of line with the frame, or fresh wet fluid around the steering gear or power steering lines.
• Free play. With the engine running and the front wheels straight, turn the wheel gently each way and note how far it moves before the front tires start to turn. Have a helper watch the tires from a safe spot beside the truck rather than in front of it.
• When it happens. Pulling only under braking, only when loaded, only on crowned roads, only after a pothole, or all the time: each one narrows the search.

When to stop driving

Some steering symptoms are not something to nurse to the next exit. Stop somewhere safe and call if the steering changes suddenly, if you hear or feel a clunk from the front end followed by a change in how the truck steers, if the wheel moves a long way before the truck responds, if the truck pulls hard enough that you struggle to hold the lane, or if you see a broken spring, a shifted axle or power steering fluid pouring out.

Pulling that has built up gradually, with nothing visibly broken, is less urgent but still needs a proper diagnosis soon, because a steering part that has worn gradually can fail suddenly.

What the service truck fixes and what goes to a shop

Suspension and steering work is on the mobile truck repair list, specifically air bags, shocks and worn steering components. Tires that are low, damaged or mismatched are replaced at the roadside, and so are brake chambers and slack adjusters when a one-sided brake is the reason for the pull. Air bags and height-control valves are roadside jobs too.

There are clear limits, and they are worth stating plainly. We do not do wheel alignments; alignment is shop work done on alignment equipment, and a truck that needs one should go to a shop that does them. Kingpin replacement and steering gear replacement are also shop work. So is anything that needs the truck on a lift, a broken spring or a shifted axle that has to be reset and clamped properly, and damaged axle positioning parts. If what we find is shop work, we will tell you, and we will tell you whether the truck is safe to drive there or needs a tow.

Help us narrow it down on the phone

Tell us whether the truck wanders, pulls or has play in the wheel, and which way it pulls. Say when it happens: all the time, only braking, only loaded, only at speed. Mention anything that came first, such as a pothole, a curb strike or recent tire or suspension work. Tell us whether one side is sitting low, whether a tire is low or flat, and whether you can see anything broken. If a flat dual is part of the story, our post on driving on a flat dual tire is worth reading first.

Sources

• 49 CFR 393.209, Steering wheel systems
• 49 CFR 393.207, Suspension systems

Related reading

Low Oil Pressure Warning on a Semi: Stop the Engine — Get off the road at the first safe place and shut the engine down.

Fifth Wheel Won't Release the Kingpin: Why and What to Do — A fifth wheel that will not release is usually binding because the tractor is pulling or pushing against the kingpin, which loads the locking jaws.

Semi Losing Power on Hills: Normal Pulling or a Fault? — Some slowing on a grade is normal for a loaded truck: weight and gearing set how fast it can climb.