IN HIS TRAVELS across America, Bob Tanis has seen some shop practices he wishes he hadn't.
Tanis, a recently retired technical trainer who works as a consultant and expert witness in lawsuits involving wheel losses, is fascinated by the methods used by mechanics to adjust wheel bearings.
Unless the shop has a mandatory bearing-adjustment procedure in place, it's possible that many technicians will admit that they still adjust bearings by how the assembly feels after they have inspected and reassembled the wheel-end components. They traditionally are taught a bearing-adjustment procedure, not a final axial end play movement value, and might benefit from more bearing-adjustment science and an investment in more tools.
Tanis tells this story of being in between classes at a south Texas facility and wandering into the shop.
“I watched a guy putting on studs to hold the wheel on,” he says. “There were 10 of them, and he was doing it with an air gun. I was talking to shop manager and I asked, ‘What torque is he using?’ The manager said, ‘Well, he should be going to 450 or 500 ft-lb, but 500 ft-lb is where we want it to be.’
“The mechanic finished putting them on with an air gun. I said, ‘What are those torques?’ He said, ‘I don't know. I don't own a torque wrench.’ I said, ‘Here, borrow mine.’ He had adjusted them around the circle instead of using a cross pattern as you should. So we put the torque wrench on first one, set it at 500 ft-lb, and actually the nut was at 160 ft-lb. It was the first one. He didn't recheck it. The next eight were between 550 and 600 ft-lb. So they were all over-adjusted. He had stretched the lug on every one of those nuts. You wonder why the studs break. That's because they've been stretched by running them up to what you think it should be, without a torque wrench and with an air gun.
“So we put it on the 10th one and he set it at 500 ft-lb, and it clicked instantly. And so we checked the breakaway torque as we did the other eight. He broke the adapter on my tool. I have no idea what that nut was at. It was so high it actually broke my wrench when he was trying to take it off.
“He was very concerned. He said, ‘Should I take it off and redo it?’ I said, ‘If you plan on replacing all the studs on that wheel, yes, take it off. If you don't plan on doing that, leave it. The damage is already done.’
“These are the scary things. He didn't even own a torque wrench, when that is a very critical factor. He couldn't even possibly get close to putting a wheel end on correctly. There's scary stuff going on out there. I've had shop managers go, ‘Oh, we do have a dial indicator. It's still in the bubble wrap.’ And you ask, ‘What can go wrong?’ A bunch.”
Tanis says there are now three different bearing systems, and each has exclusive bearings that involve different adjustment procedures.
“Typically, the double-nut adjustable system. When you get into conventional wheel ends, you need to follow Technology & Maintenance Council's (TMC) Recommended Practice 618 in adjusting the nuts. The most important aspect of that is using the dial indicator when you finish, because of the many variables involved in components as well as the equipment used to install them. For instance, was your torque wrench calibrated in last 12 months? Did you click it once or twice when you made adjustments? With all the variables, if you don't check it with dial indicator, you're not sure where you're at.”
“They typically use a cone or spacer between the two bearing sets, and it contacts the inner race of the inner and outer bearing, so your end play is set by the dimensions of that spacer or cone. Therefore, you adjust it to the manufacturer's recommendations, typically 300 ft-lb on the adjusting nut.”
“You put it on with anywhere between 500 ft-lb and 770 ft-lb of force, depending on the manufacturer. The wheel-end adjustment is designed into the system, whether it's a packaged bearing or whether the inner races are cut into the hub. But they come as a unit. You cannot maintain them. You replace them if they malfunction.”
Says Tanis, “The other aspect is, how does this apply to single-nut systems? You first follow the hub manufacturer's recommendation if you have a specialized hub. If you don't have a specialized hub, then you use the nut manufacturer's instructions to adjust that nut. And if you're putting the single-nut system on a conventional system, you follow RP 618 and need to adjust it and measure it with a dial indicator.”
The purpose of RP 618 is to “achieve a verifiable wheel bearing end play of 0.001” to 0.005” (0.025 mm to 0.127 mm).”
RP 618's service procedures apply to steer, drive, and trailer axle assemblies using conventional double-nut or single-nut systems. It recommends following the service procedures carefully to prevent premature wheel-end component failure and increase seal and bearing life. ABS (anti-lock braking systems) and traction control systems with wheel-end sensing require precise bearing adjustment to function properly.
The RP details proper service procedures for D-type, bendable-type, and dowel-type spindle nut washers. (For single nut self-locking systems, consult manufacturers' instructions.)
“If you have a system that differs from what is indicated in this procedure, consult the vehicle manufacturer's recommended procedure.
“WARNING: Never work under a unit supported by only a jack. Always support the vehicle with stands. Block the wheels and make sure the unit will not roll before releasing brakes.
“CAUTION: If your axle is equipped with spoke wheels and the rim clamps have been disassembled to remove the tire and rim assembly, the tire and rim assembly must be reinstalled and the rim clamps properly torqued BEFORE adjusting the wheel bearings. Failure to do this may result in improper wheel bearing adjustment.
“Step 1: Lubricate the bearing with clean axle lubricant of the same type used in the axle sump or hub assembly. IMPORTANT: (a) In oil bath systems that rely on differential fill to provide lubricant to the wheel seals, do not pack bearings with grease before installation. Grease will temporarily restrict or prevent the proper circulation of axle lubricant and may contribute to wheel seal failure. (b) Never use an impact wrench to adjust wheel bearings.
“Step 2: After the wheel hub and bearings are assembled on the spindle or axle tube, torque the inner (adjusting) nut to 200 ft-lb while rotating the wheel hub assembly.
“Step 3: Back off the inner (adjusting) nut one full turn. Rotate the wheel.
“Step 4: Re-torque the inner (adjusting) nut to 50 ft-lb while rotating the wheel hub assembly.
“Step 5: Back off the inner (adjusting) nut.
“Step 6: Install the locking washer. If dowel pin and washer (or washer tang and nut flat) are not aligned, remove the washer, turn it over, and reinstall. If required, loosen the inner (adjusting) nut just enough for alignment. IMPORTANT: Never tighten the inner (adjusting) nut for alignment at this point of the procedure. This may pre-load the bearing and cause premature failure.
“Step 7: Install and torque the outer (jam) nut. NOTE: This adjustment allows the wheel to rotate freely with 0.001“ to 0.005“ (0.025 mm to 0.0127 mm) end play.
“Step 8: Verify end play with a dial indicator. Wheel end play is the free movement of the tire and wheel assembly along the spindle axis. (a) Make sure the brake drum-to-hub fasteners are tightened to the manufacturers' specifications. (b) Attach a dial indicator with its magnetic base to the hub or brake drum. (c) Adjust the dial indicator so that its plunger or pointer is against the end of the spindle with its line of action approximately parallel to the axis of the spindle. (d) Grasp the wheel assembly at the 3 o'clock and 9 o'clock positions. Push the wheel assembly in and out while oscillating it to seat the bearings. Read bearing end play as the total indicator movement. NOTE: If end play is not within specification, readjustment is required.
“Step 9: RE-ADJUSTMENT PROCEDURE. If end play is too loose, remove the outer (jam) nut and pull the washer away from the inner (adjusting) nut, but not off the spindle. Tighten the inner (adjusting) nut to the next alignment hole of the washer. Reassemble the washer and re-torque the outer (jam) nut. Verify end play with a dial indicator. If end play is not present, remove the outer (jam) nut and pull the washer away from the inner (adjusting) nut, but not off the spindle. Loosen the inner (adjusting) nut to the next alignment hole of the washer. Reassemble the washer and re-torque the outer (jam) nut. Verify end play with a dial indicator.
“FINE TUNING THE ADJUSTMENT: If, after performing the readjustment procedures, end play is 0.004"-0.005" (0.102 mm - 0.127 mm) range, repeat the appropriate procedures, removing the washer from the spindle, tighten or loosen the inner adjusting nut the equivalent of 1/2 of an alignment hole of the washer, or reversing the alignment washer, and reinstalling it onto the spindle. Reassemble and re-torque the outer (jam) nut. Verify end play with a dial indicator. NOTE: Bendable-type washer lock only: Secure nuts by bending one wheel nut washer tang over the inner and outer nut. Bend the tangs over the closest flap perpendicular to the tang. CAUTION: Before operating the unit, the wheel hub cavities and bearings must be lubricated to prevent failure.”
Tanis says that if you asked 10 different mechanics how to adjust a wheel end, you'd get 10 different answers.
“Their techniques may or may not work,” he says. “They learned it one of three ways: from reading the instructions, from trial and error, or from some guy who retired four years ago. You don't know what you have in adjusting the wheel end unless you use a dial indicator. Typically they don't do that. I've seen people use an air gun to adjust wheel ends, which you can't do.
“The next fallacy is not identifying that they have a specialized hub, a pre-adjusted or unitized, trying to replace the parts in a unitized or not doing the proper adjustments if it's a pre-adjusted.
“Its important, too, that they make sure they put a locking device on any of the nut systems. Some of it's the tang washers that you bend. Some of it's putting a set screw through, joining the two nuts together. If you eliminate that aspect of it, then the nuts on the left side of truck will back off and the ones on the right side will get tighter. That's why typically you'll have wheel-offs on the left side versus the right side.
“If you get a wheel end too tight, it'll actually melt the fasteners. If you get it too loose, you'll beat against the fasteners, mushroom them, and the unit will finally bend them so much that the whole wheel assembly will leave the axle.
“Mechanics go with whatever method they've learned. Some of them just tighten it to 50 ft-lb or 100 ft-lb, or whatever they learned at, and leave it. Even if they follow RP 618 to the letter, they could come up with the wrong answer because it's not up to 0.005" end play. In reality, if you can measure the end play, it can't be in pre-load because you don't want to be in pre-load, because then you don't know where you're at. If you can measure the end play and it's less than 0.005", you're good to go.
“If you don't adjust it properly and you have a failure, one of two things will happen: The wheel is going to come off or it's going to burn up, and neither one is good. And it's extremely important you do it right. A conventional wheel end is where the most variables are, and that's where you have to follow RP 618 and use a dial indicator when you're finished with your adjusting procedure and you use a dial indicator after you put on a jam nut or after its locked. And never use an air gun. If you're going to use an air gun, you run it up short of where you want to go and then finish it with a torque wrench.”