An integrated wheel end system refers to a self-contained hub assembly on heavy trucks and trailers that integrates the wheel bearings, seals, and hub into one pre-assembled unit.
This integrated design offers several benefits over traditional hub assemblies:
- Simplified maintenance – Integrated hub assemblies are easier to install and service compared to assembling individual components. The sealed bearings and hub are pre-adjusted so no end-play adjustments are needed.
- Enhanced durability – Integrated seals and precision bearing adjustment from the factory lead to longer service life and improved reliability. The components work together as an optimized system.
- Reduced contamination – Integrated seals help prevent contaminants from entering the wheel end and degrading the lubricant. This prolongs component life.
- Improved safety – Factory integration and adjustment ensure proper preload on the wheel bearings for safe operation. Loose bearings are a common cause of failures in non-integrated designs.
Integrated wheel end systems are now used on most heavy trucks and trailers in North America.
The sealed for life design eliminates the need to periodically repack the wheel bearings with grease.
Integrated wheel end systems reduce maintenance costs and downtime for fleets while providing enhanced durability and safety.
Common Failure Modes
Wheel end components like bearings, seals, fasteners, and hubs can fail for a variety of reasons. Some of the most common failure modes include:
Bearing Failures
Bearings support the wheel hub and allow it to spin freely. Over time, bearings wear down through normal use.
Excessive wear leads to looseness, noise, and eventual failure. Contamination from dirt, moisture, or grease breakdown accelerates bearing wear.
Overheating and improper lubrication also damage bearings. Failed bearings must be replaced immediately to avoid catastrophic wheel separation.
Seal Failures
Seals keep lubricant in and contaminants out of the wheel end. Normal wear, tears, cuts, and installation damage can all cause seal failure.
Once seals fail, lubricant leaks out and contaminants enter, leading to accelerated wear of bearings and other components. Failed seals should be replaced promptly.
Corrosion
Exposure to water, road salt, and chemicals corrodes metal wheel end components.
Corrosion damages mounting surfaces, fastener threads, seals, bearings, and electrical connections.
Thorough cleaning and use of corrosion-inhibiting lubricants help prevent corrosion damage. Heavily corroded parts may need replacement.
Loose Fasteners
Vibration during normal operation can loosen wheel end fasteners over time. Loose fasteners reduce clamping force on bearings and allow more movement.
This accelerates wear and can lead to catastrophic separation of the wheel if left unchecked.
Regular fastener inspections and proper torquing is critical to avoid loose fastener issues.
Bearing Failures
Bearing failures are one of the most common issues with integrated wheel ends. This is often due to improper installation, contamination, or excessive load.
Causes
- Improper Installation – If bearings are not installed correctly, with proper preload, this can lead to premature failure. Technicians must follow manufacturer procedures carefully.
- Contamination – Any contamination of the bearing grease can cause wear. Common contaminants are water, dirt, or even the wrong grease. Seals must be intact to prevent ingress.
- Excessive Load – Overloading the wheel end beyond the rating of the bearing can cause failure. Loads should be calculated properly.
Symptoms
- Noise – Grinding, squeaking or other noises from the wheel end indicate a bearing issue.
- Looseness – Any looseness or play in the wheel when rocked indicates loss of preload.
- Leaks – Grease leaks around seals point to seal damage and bearing wear.
Solutions
- Replacement – If a bearing is worn out, it must be replaced with the exact OEM part per manufacturer guidelines.
- Maintenance – Regular cleaning, lubrication and inspection will maximize bearing life. Contamination must be avoided.
- Load Monitoring – Keep loads within specifications to prevent overload failures.
Seal Failures
Seals play a critical role in protecting wheel end components from contamination. Over time, seals can fail due to normal wear, improper installation, or damage from road hazards.
Failed seals will result in oil leaks and allow contaminants like water, dirt, and road salt to enter the wheel end.
Some common symptoms of a failed seal include:
- Visible leaks around the wheel seal area, usually accompanied by oil drips on the brake components or wheel
- Grease or oil splattered on the inside of the wheel rim
- Evidence of rust/corrosion on wheel end components due to moisture ingress
- Contaminants like dirt visible inside the wheel end or on internal components
- Abnormal noise from the wheel end, potentially from contaminated grease
If a failed seal is detected, the wheel end should be disassembled and inspected. The seal will need to be replaced to prevent further contamination.
Proper seal selection and installation is critical for long service life. Technicians should take care not to damage the seal during installation.
The mating surfaces should be cleaned and inspected to ensure no defects are present.
Applying grease on the seal lip during assembly can help prevent dry starts and ensure proper sealing.
Replacing failed seals promptly can prevent more extensive repairs down the road.
Regular inspections and planned seal replacements at manufacturer intervals can also help avoid unplanned downtime from seal failures in the field.
Corrosion
Corrosion is a common cause of failure in integrated wheel ends. Water and road salts can seep into the wheel end and cause corrosion on components like bearings, fasteners, and mounts.
Over time, this corrosion can lead to premature wear, looseness, and even component fractures.
There are a few main causes of corrosive damage in wheel ends:
- Water ingress – Contaminants like water and salt can enter the wheel end through damaged seals, breathers, or other openings. Once inside, the water allows corrosion to form.
- Road salts – Salts used for winter road treatments are highly corrosive to steel components. As the wheel rotates, it picks up these salty solutions and brings them into the wheel end.
- Dissimilar metals – When two different metals are used together, like steel and aluminum, galvanic corrosion can occur. This greatly accelerates corrosion damage.
The most susceptible components to corrosion damage include:
- Bearings – Corrosion on the bearing races, rollers, and cages can cause premature wear, flaking, and bearing failure.
- Fasteners – Corrosion on fasteners like wheel studs, hub nuts, and mounting bolts can lead to fracture, stripping, or coming loose.
- Mounts – Corrosion on suspension mounts and brackets reduces strength, leading to cracking or detachment.
There are a few ways to combat corrosive damage:
- Protective coatings – Applying corrosion-resistant paints, undercoating, or greases to components can provide an extra layer of protection.
- Regular inspection – Frequently checking for early signs of corrosion allows proactive repair before major damage occurs.
- Improved sealing – Upgrading seals, breathers, and gaskets prevents contaminant ingress into the wheel end.
With proper preventative measures, the effects of corrosion on integrated wheel ends can be minimized for improved safety and service life.
Careful inspection paired with protective coatings and improved sealing helps ward off this common failure mode.
Loose Fasteners
Loose fasteners are a common cause of problems in wheel ends. Vibration and road impacts can cause fasteners like wheel studs, hub bolts, and brake hardware to loosen over time.
This can lead to a variety of issues:
Causes
- Improper torque – If fasteners are not torqued to the correct spec initially, they are more likely to loosen. Proper torque specs vary by application and component.
- Vibration – The constant forces from vibration during driving can cause threaded fasteners to loosen. The more vibration, the faster they loosen.
Symptoms
- Clunking noises – As fasteners loosen, you may hear clunking noises from the wheel end when going over bumps or during braking. This indicates looseness.
- Wobbling – Loose fasteners can allow components like wheels and brake drums to wobble or move excessively. This may be visible upon inspection or lead to vibration issues.
Solutions
- Re-torque fasteners – Loose fasteners should be cleaned, reapplied with thread locker, and torqued to spec. This may require partially disassembling the wheel end.
- Use thread locker – Applying a medium-strength thread locker helps prevent fasteners from loosening. It should be reapplied anytime fasteners are disturbed.
- Check torque – Fasteners should be checked periodically to ensure they are still tight. How often depends on the application and driving conditions.
Properly torquing fasteners and using thread locker can help prevent loosening and potential wheel end issues down the road. Periodic inspections are key to catch any looseness before major problems occur.
Maintenance
Proper maintenance is critical for avoiding integrated wheel end failures. This involves regular inspection, lubrication, and component replacement when needed.
Inspection Intervals and Procedures
- Visual inspections should be conducted frequently, such as during pre-trip inspections, to check for leaks, loose or missing fasteners, cracks, rust, and other signs of damage. Any issues should be addressed immediately.
- More thorough inspections should occur at regular intervals as recommended by the manufacturer, such as every 6 months or 12,000 miles. This involves disassembling components to check for wear, corrosion, proper lubrication, and smooth operation.
- When inspecting, look closely at seals for leaks or tears. Check bearings for smooth rotation without play or noise. Ensure fasteners are tightened to spec. Examine all parts for rust, pitting, or other deterioration.
- Follow OEM procedures for properly disassembling, cleaning, inspecting, re-lubricating, and reassembling components. Use torque wrenches when tightening fasteners.
Lubrication Schedules and Methods
- Wheel end lubricant should be replaced at intervals specified by the OEM, usually around 100,000 miles. Shorter intervals may be needed for severe duty cycles.
- Only use lubricants meeting OEM specifications. For most applications, NLGI #2 lithium complex grease is recommended. Avoid mixing greases.
- Thoroughly clean and repack bearings when replacing lubricant. Pump grease through the hub until fresh grease purges out the seals. This indicates all old grease is flushed out.
- For oil-lubricated systems, drain used oil and refill with new oil per OEM procedures. Check seals and gaskets for leaks.
When to Replace Components
- Bearings should be replaced if inspections reveal damage, corrosion, embedded debris, excessive wear, or when they have reached their maximum recommended service life.
- Seals should be replaced if leaking, torn, or otherwise damaged. Proactively replace seals during major maintenance intervals.
- Fasteners and other components should be replaced if damaged or extremely corroded. Rusty fasteners can result in improper torque.
- Follow OEM guidelines for routine replacement intervals of bearings, seals, gaskets, and other wear items. This prevents failures and extends wheel end life.
Proper maintenance keeps all wheel end components in good working order, avoiding premature failures, extending service intervals, improving safety and reliability. Consistent inspection, lubrication, and strategic component replacement is key.
Diagnosing Failures
Diagnosing issues with integrated wheel ends starts with understanding the common failure modes and associated symptoms.
Being able to quickly and accurately diagnose problems allows for preventative maintenance or repair before catastrophic failure occurs.
There are three main techniques for diagnosing wheel end issues:
Noise/Vibration Analysis
Carefully listening for new noises or feeling for vibrations coming from the wheel end can reveal problems.
Bearing failures often lead to grinding or rumbling noises. Excessive seal wear allows contaminants in, which can cause clicking or scraping sounds.
Loose fasteners will click or clunk when the wheel hits bumps. Any new vibration or noise likely indicates an issue needing attention.
Leak Checks
Seal failures will result in leaking lubricant. Look for wetness around the wheel end, hub, and brake components.
Oil slung around the wheel can also indicate a seal leak. Sniff the wheel end – the smell of oil is a giveaway.
Leaks mean at minimum the seals need replacement, but further damage may have already occurred.
Play/Looseness Checks
Excess bearing play or looseness of the wheel on the hub indicates wear, incorrect installation, or loose fasteners.
Try rocking the wheel top to bottom and check for clunks. Spin the wheel and feel for any wobble.
Use a dial indicator to precisely measure any play or runout. If the wheel has noticeable looseness, the bearings need inspection and potential replacement.
Repair and Replacement
Deciding whether to repair or replace a failed wheel end component depends on a few key factors.
When to Repair vs. Replace
- Severity of damage – If the damage is relatively minor, such as worn seals or bearings, repair may be feasible. But if there is severe damage like a cracked hub, replacement is likely needed.
- Part availability – Some wheel end parts may no longer be available from the OEM. In that case, repair may not be possible.
- Cost – In some cases, repairing a component is more cost effective than replacing it. But replacement costs can be lower for inexpensive parts.
- Expected remaining service life – Repairing worn parts that are nearing the end of their typical service life provides less value than replacing them.
In general, repairs make the most sense for inexpensive components with minor damage and significant remaining service life. Major damage or parts near the end of their lifespan are better candidates for replacement.
Installation Best Practices
Proper installation is critical to achieve maximum wheel end service life and prevent premature failures.
Here are some best practices:
- Follow OEM bolt torquing specifications and sequences to ensure proper clamping force. Under or over tightening can lead to component damage or loosening.
- Use thread locker on wheel studs and other threaded fasteners per OEM recommendations to prevent loosening.
- Thoroughly clean all mounting surfaces, studs, and fastener threads to prevent contamination and ensure proper torque.
- Replace seals, gaskets, cotter pins, and other secondary hardware when replacing hubs or drums. Don’t reuse these parts.
- Confirm the wheel bearing adjustment is correct after installation to avoid premature bearing wear or failure.
OE vs. Aftermarket Parts
OE parts from the original manufacturer offer a high level of fit, finish, and durability since they are designed for that specific application.
But they are often the most expensive option.
Aftermarket parts can provide a lower cost alternative. However, quality can vary significantly between different aftermarket brands.
Parts that are reverse engineered to OE specifications and manufacturing standards tend to offer the best value and durability.
For critical components like wheel bearings, OE or premium aftermarket parts are recommended when possible.
For secondary hardware like seals, less expensive aftermarket parts may be acceptable if they are from a reputable brand.
Proper installation and maintenance practices are key to maximizing part life regardless of original source.
Summary
Wheel end failures can lead to a range of issues from minor vibrations to catastrophic events, so proactive maintenance is critical.
By understanding the most common failure modes like bearing and seal failures, corrosion, and loose fasteners, fleets can diagnose problems early and prevent breakdowns.
Regular inspections, lubrication, and replacing components at recommended intervals will extend wheel end life dramatically.
Catching small problems before they cascade into larger ones also reduces repair costs and downtime.
Failure to maintain wheel ends properly frequently results in unplanned road service, towing fees, and lost revenue from out of service vehicles.
While the consequences of a wheel end failure can be severe, they are entirely preventable with vigilance.
By making wheel ends a priority in preventive maintenance programs, fleets can avoid issues down the road and keep their trucks running safely and efficiently.
