“It’s part of a system; you can’t set it on a bench before you put it in,” he cautions. “The valve selection and the linkage subsystem and the specifications associated with the valve—the ride height and the linkage—are all part of the total suspension package. The OEM has the final call as far as what valve he chooses, the linkage he chooses, and that’s appropriate for determining what the ride height is at, based on where and how the valve, linkages and lines are installed.”
The trouble is, a lot of things can affect the adjustment of the ride-height valve and linkage.
“It could be just basic wear of the components over time,” says Petresh. “The valve wears, the linkage arms that are attached to the valve assembly—you’ve got one rod between the lever attached to the valve and another attachment point on the axle, or suspension arm—they wear over time, get sloppy, lazy. The linkage connections are vulnerable to damage: road contamination, ice, snow—it gets wiped out, damaged by the environment quite often.
“The technician also should have some idea as to what his ride height should be, within limits, without going through some exhaustive, complicated diagnostic procedure; that’s not necessary until he suspects he’s got an issue,” he says. “He should be able to determine from experience, by the way the vehicle is set up and spec’ed, to know whether it’s sitting properly or not. And that’s really a routine PM check, based on his operation.
“A lot of times the driver should pick it up,” Petresh continues. “If you’ve got a reasonably competent driver who knows what he’s doing, he’ll pick up that vibration. Because when your ride height goes to hell, your driveline angles are out of whack. So then he starts feeling vibration problems and a halfway decent driver is going to feel that. It’s obvious: that’s the biggest clue and the first clue.
“Of course, if you’ve got a camber side-to-side, or the one axle drops down, then you know you’ve got a major problem,” Petresh says. “And usually one of the other things, the adjustment or the height, slips out of position, prior to having a major meltdown—a broken arm, a total valve malfunction or a linkage failure—it’s either been busted or knocked off or it’s worn to the point that you no longer get any decent engagement.”
Clearly, there’s a lot here that the technician needs to be aware of.
“This is critical,” says Hendrickson’s Nash. “A technician really needs to periodically check the height of the suspension. If you don’t…
“I came out of the transmission business over at Meritor, and one of our biggest problems there was synchronizers getting knocked out, and they get knocked out because the driveline angle is off,” he says. “And the biggest culprit for having the driveline angle off is the air-ride height being wrong. You can lose u-joints, you can lose transmission synchronizers, drivers complain of driveline noise.”
“The first step,” says Ridewell’s Barton, “is to make sure they DO inspect. That should be part of the PM schedule.
“They should be looking at the leveling valve,” he says. “Air suspensions will typically have a leveling valve in the system—perhaps just one leveling valve for a series of suspensions. They will need to check that to make sure that it’s set properly, at the right ride height, that it’s functioning correctly. The other things to look at are the air springs on the suspension, to ensure that they’re not cracked or need replacement. I would say that typically you need to take a look at air lines; are they chafing any part of the frame structure, where perhaps you could have a failure going down the road, where a line would bust through because of chafing?”
“The pneumatic controls are probably the most vulnerable, the most susceptible to damage and abuse and wear of anything on the suspension. I don’t think people recognize that,” says Haldex’s Petresh. “I’m in charge of our nationwide field service staff, and I get all my guys together quarterly to review things like this and try to figure out the best way to go after it, new manuals or instruction sheets; we’re always looking for a better way to get that message across. But technicians don’t realize that the controls are not boilerplate like the rest of the suspension is, and as a result they don’t pay any attention to it. It’s just neglected because of this awareness thing. They’re just not aware of it.”