STEER AXLE SMARTS
Don't let the term 'maintenance-free' fool you.
Deborah Lockridge
Senior Editor
Are your technicians unloading the steer axle when they inspect it? If not, you're probably among a number of companies that have been lulled into thinking "maintenance-free" and "extended-maintenance" components are guaranteed trouble-free.
That's the word from the folks at the American Trucking Associations' Technology and Maintenance Council.
"It's scary, the number of shops I've been into and when I ask them to lift the steer axle, they spend most of the time trying to find a jack that will do it," said Bob Rosenthal, former national service manager for ArvinMeritor, at TMC's annual meeting earlier this year.
Rosenthal was moderating a session exploring a new TMC Recommended Practice – RP 651, which at press time was still in final revisions before formal adoption.
TMC's S.6 Study Group, which is devoted to chassis maintenance, saw a need for this RP because, with the advent of "maintenance-free" and extended-maintenance components, a number of traditional maintenance activities have been eliminated in some PM programs, especially with respect to tie rod ends, U-bolts and wheel ends.
So a task force was formed to develop an RP highlighting the basic elements of a commercial vehicle steer axle maintenance program.
The resulting RP divides the steer axle assembly into four subject areas: suspensions, axles, wheel ends and lubrication. For each, a "general" inspection and a "detailed" inspection/adjustment procedure is laid out. The idea is that the general inspections should be done at each PM, and that will determine if a detailed inspection is needed.
Two of the main concerns discussed at the TMC session were the need to unload the steer axle for inspection and the importance of technicians knowing what's under the hubcap.
Unloading The Axle
"I've seen people try to check end play on steer axles by kicking the pinch bar with the vehicle on the ground," Rosenthal said. "One of the key things is that you have to look for wheel-end looseness. I don't care what it's caused by. You can't just take a pinch bar and sit there on the floor with a loaded axle and say whether that's good or bad."
Whether you're performing a general or a detailed inspection, it needs to be done with the axle in an "unloaded" condition – wheels off the ground, with the vehicle supported at the frame. The parking brake should be on, drive wheels blocked and safety stands supporting the vehicle load.
With the axle unloaded, you can check for wheel end looseness by pushing and pulling on the tire. If movement is felt, apply the service brake and repeat with brake applied. If movement is still present, then you need to take a closer look at the knuckle. If not, you've got a wheel end problem.
The importance of unloading the axle is not only true for checking end play. For instance, you can check for binding or resistance at the wheel end, which could be a sign of improper bearing adjustment, contamination, internal component failure or a brake dragging. Noises heard while rotating the wheel end assembly, such as clicking, scraping or grinding from inside the wheel end, could indicate component failure.
Suspensions, except for checking ride height, should be inspected in the unloaded condition – springs, shock absorbers, shackles, spring pins, bushings, etc. The unloaded position allows you to inspect tie rod ends and cross tube assemblies.
In addition, many parts of the axle assembly should be lubed with the axle in an unloaded position, which is not being done in many cases.
Under The Hubcap
If you don't know what sort of bearing package is behind the hubcap, you don't know what type of maintenance needs to, or can be, performed. Some wheel ends are not field serviceable and disassembly may void the warranty.
"Proper steer axle maintenance isn't difficult or complicated, but it can be confusing for your technicians if they don't know what type of wheel end they are working with," said Wes Smith, director of maintenance at Missouri-based CFI.
There are three types of wheel ends:
• Conventional or standard wheel end – Also called a manually adjusted wheel end, this provides the means to set end play or achieves a slight amount of preload during operational maintenance procedures.
• Factory pre-adjusted wheel end – A preset amount of end play or a slight amount of preload is achieved either by locating a spacer between the inner and outer bearing cones or through use of a shoulder machined into the axle spindle. These units are commonly field serviceable. They are the most popular on today's Class 8 steer axles.
• Unitized wheel end – Internal components on these wheel ends are not field serviceable and should not be disassembled. A preset amount of end play or a slight amount of preload is obtained during the manufacture of the component assembly. These usually have a special hubcap and can be easily identified.
Unitized and pre-adjusted wheel ends have identification markings either on the hubcap or on a supplemental ID ring located on or near the axle spindle nuts.
Other Tips
• If you suspect a problem with your shocks, the only proper way to inspect them is to conduct a heat test. Take the vehicle out over some rough road for 15 minutes to get the shock working. Touch the frame for ambient reference, then lightly touch the shock body. It should be warmer than the frame; that means the hydraulic fluids are heating up and it's working. If it's cold, it needs to be replaced. With today's shocks, removing the shock and doing a push in/pull apart check for force won't tell you much.
• Lubrication is key. On wheel ends, lack of lubrication can cause bearing problems and lead to catastrophic failures – in other words, wheels coming off.
Wheel end lubricant is normally replaced any time the wheel end is removed from the axle for service. Before you dispose of that lube, give it a good look for things such as metallic particles, contamination, foaming, color and smell, all of which can indicate problems inside the wheel end. (Lubricant is not serviceable in unitized wheel end hubs.)
