When considering the average mileage of most commercial motor vehicles, considering the load and job type, wheel bearing replacement generally occurs between 90,000 and 120,000 miles. Still, regardless of the vehicle’s age, it is prudent to inspect the wheel bearings any time you are also doing brake replacement work or brake inspections.
Most OEMs recommend brake lubrication at around 25,000 miles for front wheel bearings. If bearings are not lubricated until each time the brakes are replaced, that is fine. Bearings can go double the time before requiring re-lubrication. Any technician or shop assistant should always be on the lookout for the signs of worn-out bearings. From friction to noise on the wheel rotation or unusual slowness, it is critical that bearings are addressed at the first sign of a problem.
When replacing wheel bearings, any shop technician worth their salt will tell you that you must replace the bearings on both hubs. The wheels will have the same mileage and be subjected to the same amount of wear, so they should get bearings at the same time. This way you can prevent unfortunate service calls and ensure the safety of your truck drivers and equipment.
Don’t assume that it is okay to stop at the bearings. Why not check the seals while you are at it? Just be very careful. Bearings are made of tough stuff but are actually composed of sensitive machinery equipment.
Unlike a tire, a bearing is not something that should be just tossed around; they must be handled with great care. Even the smallest mishandling of a bearing, whether during transport or installation, can damage internal components. Damage can lead to premature failure and a cascading of effects to other equipment on the truck.
When working with a bearing, there is a cardinal rule all technicians should live by: Dirty is deadly. Always make sure your work area is as clean as possible – although, let’s face it, you should be doing this anyway as a best practice. The fact is, even the tiniest of dirt or particular matter can damage a bearing internally and lead to a shorter lifespan.
Bearings must also be installed with the proper tools. Removal and installation cannot be handled with a screwdriver, wrench, and hammer. With the right tools, the job can be done more accurately and efficiently. Never hesitate to consult the vehicle’s manual when going through a mounting procedure. Technicians should never rely on simple gut instinct or be too proud to consult a manual.
The most important part of a bearing install or replacement is the mounting force, which is why consultation may be required. If improper force is applied, the indentations in the bearing raceways will eventually lead to other parts of the bearing failing. The same occurs if a seal is not mounted properly. If a bearing replacement has occurred and a truck driver is already hearing noise while on the road, the shop needs to take a second look at the job.
Bearing replacement best practices include:
- Utilizing clean tools.
- Using the proper grease.
- Operating in a clean workspace.
- Checking the contact surface for the seal lip.
- Avoiding using a blunt object to hit the bearing if you are having a problem using physical force.
- Avoiding setting clearances on the hub units.
- Hub unit clearances are set at the factory.
- Checking the condition of the housing and axle when changing the bearing.
- Not taking a hub unit apart before mounting it.
- Not attempting to move or adjust the seal on the hub unit.
Remember, even the smallest mark, rust, or debris could damage a seal lip and will allow water to penetrate the bearing and induce corrosion. Many bearings are also already set at the factory with the correct preload. Use the workshop manual if you need to tighten the nut to the correct preload. Also, keep in mind that the bearings are set to the correct clearance preload at the factory.
The last thing you ever want is for a raceway seals to be damaged and the bearings eventually destroyed, otherwise the unit will fail prematurely. Premature failure, water penetration and corrosion are your worst enemies.
Steering Clear of Defects
Well, the annual CVSA road check just passed and this time they put a special emphasis on checking steering and suspension. The 72-hour Roadcheck blitz wanted to look closer at components that tend to be fairly reliable and do not require a lot of shop time. For this reason, shops tend to overlook these components. As they age, problems can sneak up. While many shop technicians more-or-less leave them alone for the first couple of years, they should never be ignored completely. In many cases, a truck requiring alignment will need some suspension work done as well.
The average four-year-old truck with 500,000 miles on it or more will generally have some undercarriage issues that need to be addressed. Things like loose U-bolts are common on vehicles with under-slung suspension systems. Considering the entirety of the truck’s weight rests on the nut, which stretches the bolt, problems are common.
When a bolt stretches too much, the axle can move within the assembly, which can cause a misalignment to occur. This could be followed by loose spring packs, cocked air springs and other problems that give shop technicians big headaches. The main problem is that suspension issues can be difficult to spot. Problems often occur underneath the suspension components. It is best that a technician looks for suspension problems on an undercarriage using a creeper.
Steering components can also be a major headache and were certainly on the viewing block at this years Roadcheck. Looking at last year’s Roadcheck event, there were 538 violations for suspension defects and 286 steering-related violations. While these might not seem like large numbers, for the fleets running those vehicles, OOS violations could be crippling to the bottom line.
Even more, steering and suspension systems are safety critical. These are the systems that support the heavy loads truckers carry. They also are vitally important for buses and utility vehicles. When a commercial motor vehicle is under acceleration and braking, proper suspension and steering systems are critical to keeping the vehicle safely on the road. They also help ensure the tires stay in alignment and reduce the chances for uneven tire wear or tire failure. Finally, they maximize contact between the tires and the road.
The Most Common Violations
Some of the most common suspension violations were missing or defective axle positioning parts. These include loose suspension tracking rods, missing or damaged spring hangers or missing, damaged, or hanging spring hangar bolts. Next up on the potential violation list were leaking air springs or air spring lines, followed by broken, missing or separated spring leaves.
When it comes to steering defects, the most common were simply worn components. Improperly welded or missing components were next on the list. When components are not worn properly, missing or misaligned, there may be too much movement within the ball and socket joint of the steering king pin. This could include loose fasteners on steering components.
Loose steering columns, leaks or looseness in the power steering system, excessive free play in the steering wheel, worn steering boxes, loose pitman arms and more, were all listed as steering violations that result an out-of-service decisions.
Not to be left out, problems with trailers were also included in the stats related to OOS violations related to suspension problems. Roadcheck inspectors found a problem that was alarming considering the safety implications, sliding-axle locking pins missing or not engaged. So, what is a shop technician to do to ensure they are not caught on the wrong end of the inspection stick?
One word: Proactive Inspections
Be Proactive, Not Reactive
You have got to get your shop in the habit of conducting proactive checks. Check the steering lash by turning the wheel in one direction until the tires begin to pivot. If there is too much play, there may be a problem. You want to mark the steering wheel at a fixed point and turn the wheel in the opposite direction until the tires again begin to move.
Where your suspension components are concerned, inspect the suspension system for indications of misaligned, shifted, cracked or missing springs. You also need to be on the lookout for loose shackles, missing bolts, unsecured spring hangars, or cracked or loose u-bolts. Signs of cracked axles or obvious misalignment should be obvious to any technician worth their salt.
Most importantly, ask your truck drivers. If they begin to feel bumps, shakes, or excessive steering play as they drive, make sure there is a process in place to reports such problems. The vehicle suspensions should support its weight and keep it level. If one side of the vehicle is resting higher than another, then you know you have a problem.
In the end, it is important to keep a close eye on such safety-critical aspects of your vehicles, from bearings to suspension and steering. This year’s Roadcheck may be over, but you never know when an inspection might be just around the corner. Don’t get caught unaware and find yourself out-of-service.