by Paul Abelson
Last month we presented some good news and some bad news about wheel ends. The good news was that thanks to advances in design, materials and manufacture, the need to maintain wheel ends will soon become history. The bad news is that older equipment will still need to be maintained, and because of poor maintenance practices, wheels are still separating from trucks.
Also last month, we wrote about how to remove and replace (R&R) bearings and seals. Now, we'll see what The Maintenance Council (TMC) recommends for lubrication and adjustment. TMC RP631A, "Recommendations for Wheel End Lubrication," examines both driven (drive axle) and non-driven (steer and trailer axle) wheel ends, using both oil and grease. Since we discussed bearing R&R last month, we'll assume we are starting with clean, dry parts, free of contamination and lubricant residue. If that is not the case, "Make it so."
Non-driven, oil lubricated For oil-lubricant wheel ends, pre-lubricate the assembly as it is being replaced. Use the same oil to be used in the hub. Do not pack bearings with grease. Align the hub with the spindle. If tires are mounted on the hub, cover the spindle threads to prevent accidental damage and use lifting equipment to align the hub and spindle. When the hub is in position, fill the hub cavity with clean oil. Install the outer bearing, washers and nuts. You are now ready to adjust bearing endplay.After bearings are adjusted (we'll discuss how later), mount the proper vented hubcap, following the suppliers specific instructions. Then slowly add oil, allowing time for the oil to seep through the outer bearing to fill the cavity. Pause for a few moments and recheck the level until you're sure the oil has reached the fill line. Either over-filling or under-filling can result in premature bearing wear. Replace the filler cap. Torque a side-fill plug to manufacturer's specifications.
Grease lubricated For grease lubricant wheel ends, use the same NLGI (National Lubricating Grease Institute) grade number as was used previously. If installing new wheel ends, select the grade you want. NLGI 000 and 00 are considered semi-fluid greases. NLGI 0 is soft and NLGI 1, 2 and 3 are hard greases. Do not use anything harder than No. 3. You might consider No. 2 grease for one major reason. It is the grease most often used for chassis lubrication, and is therefore readily available.After cleaning all residue or debris, pack both the inner and outer bearing cones full of grease. Work the grease into the bearing from the narrow side of the taper to the wider side. Make sure grease has gone under the bearing cage and to the roller ends. Place a light protective film of grease on all wheel end components before installing them.As with the oil-filled wheel ends, install the hub on the spindle. Use lifting equipment if needed. With the hub supported, before installing the outer bearing cone, fill the hub with grease until the hub is halfway filled (to the three o'clock and nine o'clock positions). Use a template to retain the grease while filling the hub. Be sure there are no air pockets. Install the outer bearings, washers and nuts. Adjust endplay with a dial indicator. Then use a hubcap appropriate for use with grease.Hard greases (including No. 2) should be packed into the hub cavity before installing the outer bearing. Before installing the hub on the spindle, hold it flat and fill the hub up to the level of the bearing races. Mount the hub as described above. Make sure the hubcap is appropriate for the grease used.
Driven It is assumed that all driven axles are oil lubricated, using the same type used in the axle. Do not pack bearings with grease. It will restrict oil flow and could contribute to seal failure. Pre-lubricate parts with oil. Install wheel seals and carefully lift the hub onto the spindle. When the hub is in place, fill the cavity with oil. Adjust bearings as described below. When installing to the flanged drive axle shaft, always use a new gasket. Torque flange nuts to the manufacturer's specs.
All wheel ends Clean up any drips or spills after installation so they will not be mistaken for leaks. After reassembly, check for signs of seepage or leaking. If none, test drive the truck. After driving, check hubs for excessive heat or differences in temperature. Check lubricant level. If low, look for signs of seepage and oil soaked brake linings.Because grease does not spread as easily as oil, look closely for grease seepage or leaks using a bright flashlight or work light. For more detailed maintenance and installation procedures, refer to TMC RP631A.
Wheel bearing adjustment TMC has developed recommendations in RP618 for adjusting wheel bearings so that bearing endplay is between 0.001" and 0.005". When bearings operate, they heat up and expand. With too little endplay, bearings are tight. The heat can make them seize. The resulting friction can score the spindle. With too much endplay, there is insufficient load on the nuts. Wheels can wobble, causing uneven tire wear as well as bearing and spindle damage. The nuts can back off. Loose spindle nuts also let bearings cock in their races. These conditions can result in spindles being worn through or, in some cases, wheel separation.Most spindles use conventional double-nut or single-nut fastening systems, although some now have single, self-locking nuts. For those systems, consult the manufacturer's instructions. Some suppliers, like the Hub Nut Corporation (313-561-8752), make specialized replacement nuts that help eliminate endplay problems.When bearings have been lubricated and assembled on the spindle or fastened to the axle tube, torque the inner (adjusting) nut to 200 lb. ft. while rotating the wheel hub assembly. Now back the inner nut one full turn, then rotate the wheel. Next, retorque the inner nut to 50 lb. ft. while rotating the wheel.For the next few steps, refer to the accompanying table. Again, back the adjusting nut the amount shown on the table, according to axle type and thread pitch. You may wonder why it is important to tighten, then back off, then tighten again and back off again. Doing so properly seats the bearing and gives it a preload so it will run true. Then it lightens the load so the bearings run freely.Now install the locking nut. There should be a mechanism to secure the locking nut: A dowel pin and washer, or a washer tang that mates with a flat on the nut. If the locking device does not properly line up, remove the washer, turn it over and reinstall. Most washers are made so that each side is one-half an adjustment off when reversed and matched to the locating keyway. You may have to loosen the inner nut just enough for alignment. Never tighten the inner nut at this stage. It will put too much preload on the bearing. Install the outer jam nut and torque according to the specifications in the table.
Verify End Play At this point, endplay should be within specification, but it must be verified using a dial indicator. Endplay is the measure of free movement of the tire and wheel assembly along the spindle axis. It is measured by attaching the magnetic base of the indicator to the hub or brake drum. Set up the instrument so the plunger is against the end of the spindle, approximately parallel to its axis.To test endplay, grab the wheel assembly with one hand at the three o'clock position and the other at the nine o'clock position. Push in and out together and alternately. Read the indicator for total movement.If endplay is excessive, remove the outer nut. Pull the washer away from the inner nut, but do not remove. Tighten the inner nut to the next alignment hole of the washer. Then reassemble and retorque the outer nut.If endplay is not present, remove the outer nut and loosen the inner nut to the next alignment hole. Reassemble and retorque.After each readjustment, measure endplay using the dial indicator.If the axle has bendable-type lock washer, verify endplay, then secure the nut by bending one tang over the closest flat of the nut. If equipped with a dowel pin and perforated washer with a key, remove the washer, loosen or tighten the inner nut the equivalent of one-half an alignment hole, then reinstall the washer and retorque. You may have to reverse the washer to make the dowel pin and the keyway line up.
Thanks to TMC for the information in this article, and for the table that accompanies it.
The information in this article is from the Recommended Practices Manual developed by TMC members and published by The Maintenance Council. You can obtain a copy by calling 703-838-1763.
Paul Abelson serves Land Line as technical editor and freelances from his office in Lisle, IL.