Determining the correct trailer bearing size is crucial for safe towing and preventing costly breakdowns. Ignoring this vital aspect can lead to bearing failure, potentially causing wheel detachment and serious accidents. The most reliable method involves physically removing the old bearing and referencing the bearing numbers etched onto its races (inner and outer rings). These numbers precisely identify the bearing dimensions, allowing you to source an exact replacement.
Why Proper Bearing Size Matters
Choosing the right trailer bearing isn’t just about getting a part that fits; it’s about ensuring the load capacity, seal compatibility, and overall performance of your trailer’s axle. Using an incorrect size can lead to premature wear, increased friction, and ultimately, catastrophic failure. A mismatched bearing can also compromise the effectiveness of the bearing seal, allowing water and contaminants to enter, accelerating corrosion and wear. This is why relying on guesswork or inaccurate measurements is never advisable.
Identifying Bearing Size: A Step-by-Step Guide
While referencing the bearing number is the gold standard, there are situations where this isn’t possible. Perhaps the old bearing is completely destroyed, or the numbers are illegible. In these cases, you’ll need to employ alternative methods involving careful measurement.
Step 1: Disassembly and Inspection
- Safety First: Always disconnect the trailer from the tow vehicle and secure it properly with wheel chocks. Wear safety glasses and gloves to protect yourself.
- Wheel Removal: Loosen the lug nuts and jack up the trailer, supporting it with jack stands. Remove the wheel.
- Brake Drum/Rotor Removal: Depending on your trailer’s braking system, you’ll need to remove the brake drum or rotor. This often involves removing a retaining clip or castle nut. Consult your trailer’s manual for specific instructions.
- Seal Removal: Carefully pry out the rear seal from the hub using a seal puller or screwdriver. Be cautious not to damage the hub.
- Outer Bearing Removal: Once the seal is removed, you can typically pull the outer bearing out by hand.
- Hub Removal: The hub should now slide off the spindle.
- Inner Bearing Removal: The inner bearing is often retained by a grease cap or a pressed-in race. You may need to use a hammer and punch to carefully tap the race out from the inside of the hub.
Step 2: Locating the Bearing Number
- Examine the Races: Carefully inspect the inner and outer races of both the inner and outer bearings. The bearing number is usually stamped or etched onto the metal. This is a standardized number (e.g., L44649, LM48548) that identifies the bearing’s dimensions and characteristics.
- Record the Number: Note down the complete bearing number, including any prefixes or suffixes.
Step 3: Measurement as a Last Resort
If the bearing number is unavailable, accurate measurement is necessary. This is a more complex process and should be done with precision using a caliper.
- Inner Diameter (ID): Measure the inner diameter of the inner race of both bearings. This is the diameter of the hole that fits onto the spindle.
- Outer Diameter (OD): Measure the outer diameter of the outer race of both bearings. This is the diameter of the outer surface of the bearing that sits within the hub.
- Width: Measure the width of each bearing. This is the distance between the inner and outer races.
- Compare Measurements: Compare your measurements with bearing size charts available online or at auto parts stores. These charts list bearing dimensions and corresponding bearing numbers. Note: Slight variations in measurements can occur. Aim for the closest match and consult with a bearing specialist if unsure.
Step 4: Sourcing the Correct Bearing
- Auto Parts Stores: Take the bearing number or your measurements to a reputable auto parts store. They can cross-reference the number and provide the correct replacement bearing.
- Online Retailers: Many online retailers specialize in trailer parts and bearings. Ensure you purchase from a trusted source to guarantee quality and authenticity.
- Bearing Suppliers: Specialized bearing suppliers can offer expert advice and a wider selection of bearings, especially for less common trailer models.
Essential Tools for Bearing Replacement
- Jack and Jack Stands: For safely lifting and supporting the trailer.
- Wheel Chocks: To prevent the trailer from rolling.
- Socket Set and Wrenches: For removing lug nuts and other fasteners.
- Pliers: For removing cotter pins and retaining clips.
- Screwdrivers: For prying and removing seals.
- Hammer and Punch: For tapping out races.
- Caliper: For accurate measurements.
- Grease Gun: For applying grease to the new bearings.
- Bearing Packer: For efficiently packing grease into the bearings.
- Seal Driver: For properly installing the new seal.
FAQs: Trailer Bearing Size
FAQ 1: What happens if I use the wrong size trailer bearing?
Using the wrong size bearing can lead to several problems, including premature wear, increased friction, overheating, and ultimately, bearing failure. This can result in wheel wobble, difficulty towing, and potentially a wheel detachment, leading to a dangerous accident.
FAQ 2: Can I use a bearing with a slightly different size than the original?
Generally, no. Trailer bearings are precision components, and even slight deviations in size can compromise their performance and longevity. Stick to the exact bearing number or measurements specified for your trailer axle.
FAQ 3: Where can I find a bearing size chart?
Bearing size charts are readily available online. Search for “bearing size chart” on Google or visit the websites of major bearing manufacturers like Timken or SKF. Auto parts stores often have these charts available as well.
FAQ 4: What does the bearing number signify?
The bearing number is a standardized code that identifies the bearing’s dimensions, including its inner diameter, outer diameter, width, and other specific characteristics. It allows for precise identification and replacement.
FAQ 5: How do I pack grease into trailer bearings?
Properly packing grease into the bearings is crucial for lubrication and preventing premature wear. You can use a bearing packer tool or manually pack the grease by forcing it into the bearing until it fills all the voids between the rollers.
FAQ 6: What type of grease should I use for trailer bearings?
Use a high-quality wheel bearing grease specifically formulated for trailer applications. These greases are typically lithium-based and contain additives to resist water washout and extreme temperatures.
FAQ 7: How often should I repack my trailer bearings?
Repack your trailer bearings at least once a year or every 12,000 miles, whichever comes first. More frequent repacking may be necessary for trailers used in harsh conditions or subjected to heavy loads.
FAQ 8: What is a bearing race?
The bearing race is the hardened steel ring that the bearing rollers or balls run on. There’s an inner race and an outer race, which are precisely matched to the bearing. Damaged races must be replaced along with the bearings.
FAQ 9: Can I reuse old bearings if they look okay?
It’s generally not recommended to reuse old bearings, even if they appear to be in good condition. Bearings are subject to wear and fatigue over time, and reusing them can increase the risk of failure. It’s best to replace them with new bearings for optimal safety and performance.
FAQ 10: Do I need to replace both bearings on an axle at the same time?
Yes, it’s highly recommended to replace both bearings on an axle at the same time. If one bearing is showing signs of wear, the other is likely to be in a similar condition. Replacing both ensures even load distribution and prevents premature failure of the remaining old bearing.
FAQ 11: What is the difference between a tapered roller bearing and a ball bearing in a trailer?
Tapered roller bearings are generally preferred for trailer applications due to their ability to handle both radial and axial loads. Ball bearings primarily handle radial loads and are less suitable for the stresses experienced by trailer axles.
FAQ 12: How do I know if my trailer bearings are failing?
Common signs of failing trailer bearings include wheel wobble, unusual noises (grinding, squealing), excessive heat at the hub, grease leakage, and uneven tire wear. If you notice any of these symptoms, inspect and replace your bearings immediately.