Wheel-offs are a serious, costly and potentially deadly safety problem.
But what do you do when you're faced with a loose wheel situation or working with a fleet that has chronic loose wheels? How do you determine the cause so that you can correct the problem?
Finding the cause of loose wheels can be as difficult as playing ``Where's Waldo?''-you know, that kid's game in which you have to study a very busy picture such as a circus scene and try to find the goofy guy wearing glasses and red and white striped shirt and hat.
There are loads of things going on in the picture and plenty of people and animals milling about, some of them wearing red and white stripes to throw you off. But you study each figure and persevere until you find the little creep.
Likewise, the same perseverance has to be given to troubleshooting disc wheel looseness. Troubleshooting loose disc wheels can be tough if you don't know what to look for and tricky even if you do. The parts on the axle end all look ``normal'' and OK until you really start to examine them and study the picture in front of you closely.
Pinpointing the causes
The American Trucking Associations' Technology & Maintenance Council (TMC) has developed a new Wheel End Looseness Troubleshooting Guide, which has some good tips you can follow when at-tempting to diagnose a loose wheel situation. I'm sure you as well as your fleet customers can benefit from this information and perhaps find the ``Waldo'' in the axle end sooner than you expected.
There are several components that can present a series of possible causes for loose wheels. Sometimes, loose wheel problems in a fleet may be the result of multiple causes. If you are faced with a loose wheel problem, check all components on a wheel end to ensure all the causes are discovered. These multiple causes may vary from vehicle to vehicle and wheel position to wheel position.
Naturally, stud-piloted and hub-piloted disc wheel systems are different, but they do have a lot of factors in common that can cause wheels to run loose.
Improper installation is probably the leading cause of loose wheels.
1. The biggest culprit in this area is lack of proper torque. The procedure for attaining proper torque consists of:
* Using a criss-cross torquing sequence;
* Tightening the nuts to the recommended torque of 450 to 500 ft. lbs.; and
* Using a calibrated torque wrench to bring the fasteners to the final torque.
Always perform the final torque while allowing the torque to be achieved as the nut is rotating. Do not run nuts up excessively tight using an impact wrench and then use a ``clicker'' type torque wrench, which may click at a setting much lower than that achieved by the impact wrench.
If any of these steps is skipped, loose wheels can be the result.
2. Lack of proper lubrication on the threads on the studs and nuts of hub-piloted wheel systems can cause loose wheels.
Look for lack of oil residue on studs and nuts. Hub-piloted systems require that one to two drops of 30-weight oil be applied to the first two to three threads of each stud and two or three drops of this same oil are applied to the swivel joint of the two-piece flange nuts. Care must be taken not to get oil on the face of the nuts or over-oil the studs. Oil on the mounting surfaces will cause loose wheels. Look for oil residue on the disc face.
3. Failure to clean wheel and brake drum mounting faces will cause loose wheels.
Look for rust, debris and lubricant on the mounting faces. A scraper, wire brush or die grinder equipped with Scotch-Brite should be used to remove all scale, rust, corrosion, lubricant and/or debris thoroughly from both mounting surfaces of the brake drum and wheels so that they are clean, smooth and dry. Make sure any lubricant is removed from the face of the wheels.
4. A cocked drum or wheel will result in loose wheels.
Make sure the wheel and drum are seated against the hub fully and resting on the hub pilot pads. Following the criss-cross torque sequence will help ensure the components are properly seated.
The condition of the fasteners also can be the root cause of wheel end looseness. Corroded, worn, damaged or stripped studs will prevent proper clamp load from being attained. Check each stud for these conditions.
Clean corrosion from stud threads thoroughly with a wire brush.
Apply one to two drops of 30-weight oil to studs used in hub-piloted systems. Replace damaged, worn or stripped studs. You can detect yielded studs by running a nut all the way down the stud threads.
If the nut hangs up, the threads are stretched and the stud is most likely yielded.
Corroded, worn, damaged or stripped nuts also will prevent proper clamp load from being attained.
Check each nut for these conditions. Replace stud and hub-piloted nuts if these conditions exist. Also, replace hub-piloted flange nuts if they do not swivel freely after lubrication.
Improper installation
One problem that most people don't look for is studs that are improperly installed. When troubleshooting a wheel system, inspect stud heads on the backside of the hub to ensure they have full contact with the hub. If you can see a space between the stud and hub, you have a problem. Bending the stud head with hammer blows when installing the stud usually causes this. Studs with bent heads have to be replaced.
Mixing fasteners (hub- and stud-piloted) and wheel types (aluminum and steel) is becoming a common cause of loose wheels. Ensure that only the type of fasteners for the wheel system being serviced is used whether they are inner and outer cap nuts or flange nuts.
Using counterfeit fasteners-or fasteners that are the wrong grade, type and dimensions-will result in loose wheels, too. Inspect the studs and nuts and replace any fastener that looks strange or has the wrong grade markings.
Fasteners used incorrectly in stud-piloted systems will prevent torque from being achieved. Ensure that left-hand threads are used on the left side (driver's side) of the vehicle and right-hand threads are used on the right side (passenger side) of the vehicle. Look for the ``R'' (right hand) and the ``L'' (left hand) on the studs and nuts.
The condition of the wheels being used on the vehicle can affect wheel end looseness, too.
A disc wheel with an out-of-flat disc face will not allow proper clamp load to be attained. To determine if the wheel is flat, inspect the wheel face using a straight edge and a feeler gauge. The disc face should be within .020 inch as measured on the gauge. Replace the wheel if it exceeds this.
Wheels with excessive corrosion also can be the cause of the problem. Corroded wheels should be refinished provided there are no signs of cracking or loss of metal thickness. Severely corroded wheels should be replaced.
Excessive paint on wheel mounting surfaces is a well-known cause of loose wheels. Check the wheel for paint runs on the mounting face and paint thickness in excess of 3 millimeters. If either of these conditions is found, have the paint removed and the wheel refinished correctly.
If you see paint that has been squeezed out around the nuts, this is an indication that the paint was not cured prior to wheel installation. This will cause loose wheels, too. Remove the excess paint and repaint the disc face again. Allow ample time for the paint on refinished wheels to cure.
Worn chamfers on stud-piloted wheels also will prevent the proper clamp load from being attained. Inspect the chamfers in the bolt holes of stud-piloted wheels. If the thickness of the chamfer is less than the thickness of a dime, replace the wheel.
Stud-piloted wheels with wallowed or elongated bolt holes will no longer be able to center the wheel on the hub and will not provide adequate area in the chamfer to attain proper clamp load either. Therefore, replace any wheel with wallowed bolt holes.
Wallowed and elongated bolt holes on hub-piloted wheels and any type of wheel that is cracked eventually will cause wheels to come off. Replace the wheel when you see these conditions.
Mixed wheel types on an axle end are not compatible. Check the wheels to ensure that only hub-piloted wheels or only stud-piloted wheels are used and that they are not mixed on the axle end. Look for pilots on the hub to determine whether stud-piloted or hub-piloted wheels should be used.
Check brake drums, hubs
While most people concentrate on wheels and fasteners, you should know that brake drums and hubs could be the cause of loose wheels, too. A brake drum mounting surface that is damaged, worn or not flat will prevent proper torque from being achieved. Check the brake drum mounting surface for problems. If any are found, the brake drum should be replaced.
Look for dirt and grease on the brake drum that will cause loss of clamp load. Clean the mounting face of all dirt, rust, debris and grease.
Improper positioning of the brake drum can hold the wheel off the hub, thereby causing the wheel system to run loose. Ensure that the brake drum is positioned on the raised step of the hub pilot and is seated fully against the hub.
In rare cases, you may find that the incorrect brake drum is used on the axle end. You will find that the wrong brake drum does not fit properly and will hold the wheels off the hub, too. It should be replaced with the correct drum.
Hubs also need to be maintained and inspected since they hold the drums and wheels on the vehicle.
Corrosion build-up on the brake drum and wheel pilots can prevent wheels from seating properly. Look for rust or debris buildup in the corner of the hub at the drum pilot. If you find corrosion on the hub mounting face, it also can cause loose wheels.
Use a scraper, wire brush or die grinder equipped with Scotch-Brite to remove all scale, rust, corrosion and debris thoroughly from the mounting surface of the hub.
If the face of a hub or a hub pilot is worn or broken, wheels will not seat properly and will run loose. Inspect the face of the hub and hub pilots for damage and replace the hub if any damage is found.
Remember, just because you find Waldo in one place doesn't mean he's not hiding in another, too. If you're faced with a troubleshooting problem, look for Waldo in the installation process, in the fasteners, wheels, brake drums and hubs.