You’ve probably never lost any sleep over a steering maintenance issue. The systems are proven and reliable and don’t require a lot of hands-on contact. Sticking to scheduled fluid and filter changes, lubrication, and visual inspections during regular preventive maintenance inspections is probably all the attention they need — at least when they’re new.
As trucks age, though, parts loosen up, hoses weather and crack, and seals wear out. Normal wear and tear of the other components in the steering system (the ball-joints, drag links, kingpins, etc.) can affect how the vehicle handles. These can lead to driver complaints about steering and vehicle handling.
A complete visual inspection should be part of a routine PM, including components that don’t typically require a lot of attention.
“You’ll want to ensure that bolts are securely torqued across the system — the Pitman arms, drag links, even the tie rods,” says Mike Bolen, Bendix’s steering reman product manager. “Check those connections to make sure nothing is loose. And it’s important to know the recommended steering fluid life, as well as the replacement schedule for the filters on the system that protect the steering gear by keeping the fluid clean.”
Regular visual inspections also should include the steering reservoir and fluid level, plus checking hoses for weathering or cracks and keeping an eye out for fluid leaks. If steering fluid is leaking out, air could be leaking in, warns Scott Jones, a senior steering product specialist at ZF.
“You need to keep an eye on the hoses from the reservoir down to the inlet of the power steering pump, including the input seal of the pump,” he says. “The input seal is a primary source of air getting into the system. And it can go either direction. I’ve seen it pull air in the system. I’ve seen it transfer [steering fluid] into the crankcase. And I’ve seen it pull engine oil into the hydraulic system itself.”
Air in the system can cause catastrophic damage to the pump due to cavitation. The same problem can arise from letting the reservoir run dry. If the reservoir is dry, then air can get in. It’s hard not to notice a cavitating pump. It makes a loud whine that any driver should recognize as unusual. In fact, any amount of air in the system will make the pump whine.
“The telltale signs of entrained air include pink-colored frothing or foam in the reservoir and/or tiny air bubbles in the fluid,” Jones says. “The bubbles will look like glitter or diamond crystals in the fluid.”
In addition to the noise from the steering pump, the driver may also notice a lumpy feel to the steering, or a chatter, like the steering wheel is vibrating.
Diagnosing Steering Complaints
When drivers write up a steering complaint, they don’t always provide a lot of information for the technicians. If the shop does not use a power steering system analyzer (PSSA), getting input from the driver can save a lot of troubleshooting time.
“Without input from the driver, where do you even start?” Jones asks. “There are so many variables that [drivers] can help isolate, such as whether the problem occurs when the vehicle is empty or loaded, or whether the problem is more noticeable when turning right or when turning left.”
You can try narrowing the problem down with an inspection of the front-end steering components, such as tie-rods, kingpins, ball joints, etc., eliminating as many variables as possible. If there’s nothing wrong with the front end, the steering gear is usually the first suspect.
“If the problem occurs only one direction, even without a PSSA test, that leads me directly to the steering gear,” Jones says. “The power steering pump doesn’t care. It’s probably going to give you the same pressure and the same flow both directions. Typically, a loss of [steering] assist in one direction only suggests a problem with the steering gear.”
The PSSA is a combination flow and pressure gauge. It guides a technician through a set of procedures to determine whether the problem is in the gear or the pump — and that matters to the bottom line.
“One of the biggest problems is that people will start replacing parts without knowing which is malfunctioning,” says Jonathon Gerke, Bendix product manager for steering. “They tend to start with the pump, because it’s cheaper, although if the gear is easier to access, they’ll start there. In any case, if they’re wrong, now they’re out the time and cost of that repair, and they still have to replace the other part.”
Sources of Trouble
Jones says the inadvertent installation of incorrect steering components, such as the wrong pitman arm or an incorrectly set drag link, can produce adverse steering effects. “You might see bump steering or brake dive because of that change in steering geometry,” he says.
Air in the hydraulic system can create symptoms some fleets mistake for a failed steering gear, says Roy Molter, marketing manager at ZF Global Commercial Steering. “You’ll see a lot of people wanting to change out a steering gear when they should have gone through an air bleed process or some basic diagnostics first,” he says.
While air in the system usually produces hard steering one direction, hard steering in both directions can indicate an incorrectly set poppet valve inside the steering gear, says Gerke.
“The poppet is an internal unloading valve inside the gear, so you don’t build pressure against the axle stops, which causes unnecessary loads across the entire steering linkage. It’s important not to rotate the steering gear input or output shaft until it’s installed on the truck and connected to the linkage with the wheels straight,” he cautions.
Technicians must also check that the axle stops are properly set so that the poppet valves are timed correctly. This provides clearance between the front tire and other components such as the frame rail, allowing free angular movement of the tire. Again, verify that all fasteners are securely torqued across the system, adds Gerke.
This article first appeared in the December 2021 issue of Heavy Duty Trucking.