SIDEBAR: An RP Is Coming…

The trucking industry is waiting for the re-write of The Maintenance Council’s Recommended Practice 631 concerning wheel-end lubrication. It aims to integrate semi-fluid grease more fully into the RP with the addition of updated lube-fill and inspection advice tailored to “00” users.

Bob Tanis, lubricant engineer with Henkel Lubricant Technologies, chairs the RP 631 Task Force and presided over a somewhat raucous meeting at the TMC annual gathering in Nashville, Tenn., earlier this year. The nearly complete draft RP was accepted overwhelmingly by those in attendance, but it needed many refinements. The final version should be published around the end of September, with final touches being applied as we went to press, during the TMC summer meeting at the end of June.

The re-write includes a four-level inspection regime for grease-lubricated wheel ends. Here’s a preview:

It begins with the driver’s pre-trip routine, suggesting he look for seepage and feel the hubs for excessive temperature.

Level 2 is a detailed external inspection to be done at PM intervals or at least annually. Among other things, it urges that the vehicle be raised to check for smooth rolling of the wheel and for excessive end play. The hub cap is not removed.

In Level 3, at intervals determined by the vehicle maker, lubricant quantity and condition are checked by pulling the outer bearing.

There is simply no other way to get an accurate picture with semi-fluid grease (this stage would be skipped with hard grease). The presence of lube on the outer bearing is part of the check, of course, and re-filling to 50% is advised.

Level 4 is only to be reached, the draft RP says, if abnormal conditions have been found in the previous stage. It involves a complete system tear-down and suggests that prematurely failed parts and lubricant samples be kept for analysis.

During the task force meeting in Nashville, an interesting suggestion came from the floor. Lorne Brock, senior technical specialist with Imperial Oil in Toronto, said Canadian cold-weather experience has proven the value of lubricating the spindle with a molybdenum-containing grease.

The purpose: to prevent fretting corrosion, which occurs in metal-to-metal contact when small particles of metal come adrift and form a very hard ferrous oxide crystal. (The damage can be extreme if corrosion gets in the bearing raceway, Brock said in a subsequent interview, and it can form in as little as two months.)

“It’s not a time issue,” he said. “It’s a matter of type of service and [ambient] temperature.” And for the benefit of the Americans in the room, Brock added that it gets just as cold in Wisconsin and in several other states as it does in most of Canada.

How do you spot fretting corrosion? In the absence of lube and/or water, this corrosion appears red, like ordinary rust. With lube present, it appears black. It forms on the bore of the bearing cone and on the spindle bearing journal, underneath the cone. A moly grease is the only solution, Brock said, because “we know it works.” Asked whether graphite would also do the job, Brock said he and his colleagues couldn’t find a graphite that was compatible with semi-fluid greases.

Tanis was looking for further comment on this point with a view to adding it to the RP, and Con Met engineer Mark Wagner agrees that Brock’s point was a good one. Contact: TMC, 703/838-1753.