In our last issue, experts from Arvin Meritor and The Timken Company offered advice on the installation and maintenance of manual-adjust and unitized wheel ends. In Part II, we continue with ConMet's PreSet®Hubs and wheel end lubrication tips from SKF Sealing Solutions.
PRESET® HUBS
"Driver pre-trip inspections are still useful but not the end of the story," declared Roger Maye of Consolidated Metco. "When PreSet and unitized hubs first hit the market, people thought they required no maintenance, when in fact they are low-maintenance. You still have to use common sense and perform required inspections.
"When you do your standard PM on the vehicle, be sure to:
1. Inspect the hub caps and seals for damage and leaks;
2. Jack the wheel off the ground and check for endplay;
3. Rotate the wheel to check for rough bearings; and
4. Check the condition and level of the lube.
"There's a lot of confusion in the industry," Maye continued. "People are confusing manual adjust, PreSet and unitized wheel ends. A unitized wheel end is replaced as a unit: it comes from the factory with the bearing installed, pre-adjusted and pre-lubricated. If you have an issue in the field with a unitized wheel end, you replace the whole unit, unlike the PreSet, which is completely serviceable in the field. You can replace any component, from a seal to a bearing; or under one part number we provide a complete rebuild kit: cups, cones, spacer and seal, to completely rebuild that PreSet hub.
Maye went over the installation procedure for ConMet's PreSet hubs:
1. Lube the spindle with Grade Two grease, and the bearing and seal with the same lube that will be in the hub;
2. Install the hub onto the spindle, keeping the outer bearing in place;
3. Torque the spindle nut to 300 ft.-lbs., with no back-off;
4. Engage the locking device;
5. If it's a double-nut, torque the outer nut to 200 ft.-lbs.;
6. Install the hub cap; and
7. Fill the hub with lube.
"Now with the PreSet and the unitized hub, you don't have to measure endplay when you do the installation. Because of the components and the close tolerance of the product, the endplay is controlled by the stack up of tolerances in the system. On a PreSet, it's controlled by the seat-to-seat spacing, where the bearing cups seat, or the race seats, it's controlled by a precision-machined spacer, and an NP series part number bearing. It's mandatory that you replace like part numbers with like part numbers, and this NP bearing is a close-tolerance bearing that allows us to achieve the end play without requiring adjustment by the mechanic.
"Even though the PreSet and the unitized hub typically require little maintenance or adjustment, we do require periodic inspection on the PreSet, as well as maintaining the lube level and cleanliness just like you would a traditional wheel end with a manual adjust bearing.
"The PreSet hub operates on a variety of lubricant types. A list of approved lubricants for PreSet hubs is available on our website. Maintenance of hubs using semi-fluid grease, has been addressed by TMC specifically, because the minimum fill level is very critical. On a traditional oil hubcap, you just put it in until the oil level is in the range marked on the PreSet hubcap. Semi-fluid grease, when you install it, must be measured during installation in some way to achieve the minimum fill level recommended by the hub, axle or trailer OEM. Semi-fluid grease is only approved for use with PreSet hubs in trailer applications, which have specific procedures and fill levels for filling with semi-fluid. Tractor applications require oil lubrication.
"One thing that's really important: technicians see these for the first time, and don't know what they're looking at: all component manufacturers have on their websites now complete service manuals, service bulletins, instructions for step-by-step inspection, installation and maintenance. So if you can identify the product, go to the manufacturer's website, and download the service information.
"If you've got a lot of mechanics in the class, you get a lot of comments like, gee whiz, we really screwed that up! That's why getting the right information before you start on these things is critical. On if you followed RP618, you would not end up with your wheel end in the right endplay range. Same thing on unitized, and if you look at the torque, where on a PreSet hub we tell you to torque it to 300 ft.-lbs., on the inner nut, and 200 ft.-lbs. on the outer nut, or if it's a one-piece nut, 300 ft.-lbs., if you go to the unitized, ArvinMeritor tells you 300-500 ft.-lbs. on the inner nut, 200-300 ft.-lbs. on the outer nut. If you look at the Volvo unitized system, it has a special nut system that torques to 740 ft.-lbs., and it's got a special locking mechanism.
"A lot of guys are getting unitized hubs standard on the vehicle, and when they service it for the first time, it's very different from what they've seen in the past, and they're struggling," Maye concluded. "The bottom line is, the PreSet and unitized hubs have made it easier for the technician. There are less things that he has to be involved in as far as setting endplay and lubricating, but... there are some basic things they need to know about the wheel end system. What he knows about manual-adjust bearings is not necessarily going to apply to PreSet or unitized."
To conclude, Maye suggested that a basic understanding of the Technology & Maintenance Council's Recommended Practice (RP) 618 and manual wheel bearing adjustment is essential, no matter what type of wheel ends your fleet uses. "A lot of shops try and do manual adjust bearings and don't even use a dial indicator," he said. "It's necessary to verify that 1-5/1000ths endplay with the dial indicator to know that you've accurately adjusted those bearings."
LUBRICATION
If Bob Tanis, technical trainer for SKF Sealing Solutions, could eliminate one term from wheel end maintenance parlance, it would be 'lube failure.'
"Wheel end failures used to always be blamed on lube failures," he said. "The weakest link in the wheel end system is the seal, and if the seal fails, the lubricant comes out. So it's easy to say, 'That's a lube failure,' when it may have been a bad seal, or bad installation, or it may have been that the bearings were going bad. But when things go bad in a wheel end, the weakest link is going to fail, and the weakest link is a seal.
"The only 'lube failure,' he declared, "is when there isn't any in there."
Like the other experts, Tanis stressed that 'maintenance-free' wheel bearings must be inspected at regular intervals. "If you have an oil lubricant," he explained, "if you have something in the system that goes bad, the weakest link dies and oil runs all over everything. If you're running with a grease system, you don't have those tell-tale signs of oil running out. You have to look for other cues. You should check the level once a year or every 100,000 miles, but many people don't do that because it's 'maintenance-free.' You've got to look at it; you've got to inspect it to make sure that something hasn't gone wrong, and there's a myriad of things that can go wrong with a wheel end."
According to Tanis, when choosing a wheel end lubricant, the most important aspect to consider is an oil's viscosity, and a grease's equivalent to viscosity: its hardness, or consistency. "If I had my preference, if I were using an oil, the product I'd use would be the synthetic transmission lubricant, for its longevity," he explained. "Second choice would be a synthetic EP (extreme pressure) lubricant, like the axle lubricant.
"And then I would prefer a synthetic over a petroleum, because in the trucking environment it's a better type of product. Synthetics have benefits in oxidation, temperature, power savings, and environmental factors. But then when you get into synthetics, you have to worry about whether it's a Group III synthetic or a Group IV synthetic. Group III are highly refined petroleum oils; Group IV is a synthetic hydrocarbon, used historically in the heavy duty trucking. Group IIIs have been allowed to be called synthetics, so you have to differentiate.
"I would prefer an oil over a grease, but the greases work very well, too," he went on. "Grease is the 'sponge' holding the oil; the oil still lubricates, but the soap thickener holds it in place." Unfortunately, that characteristic of grease makes it more maintenance-intensive. "In order to check the level of an oil, all I have to look at is the sight glass," Tanis explained. "In order to check the level of a grease, I've got to pull the outer bearing."
"Grease hardness classifications are 000, 00 (semi-fluid), 0 (soft), One, Two, Three, Four, Five and Six (hard)," said Tanis. "Typically a chassis lube is a Number Two Grade. Anything between a Number Two and a 00 would work well in a wheel end application."
Tanis' last word was a warning: "Do not mix lubes. Sometimes technicians think they can mix a transmission oil with an axle lubricant, and there can be an additive incompatibility. If you're using greases, typically you're all right if you keep to the same soap thickener, but you could still have minor reactions between the additive systems. The supplier of your lubricants could give you a guide, but if you don't mix them, you're ok."
