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.
"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.