How to Adjust Trailer Bearings

Why bearing adjustment matters

Trailer bearings don’t stay set forever. On a boat trailer, adjustment is especially important because the hubs and bearings are exposed to both road stress and frequent water immersion. Over time, bearings can loosen or tighten, which impacts safety and performance.

You may need to adjust your bearings if:

Break-in and Settling: After initial installation or repacking, bearings can “seat” deeper into the races, reducing preload and creating extra play.
Normal Wear: Over time, grease compresses, seals wear, and vibration can loosen the adjustment.
Seasonal Maintenance: Trailers often sit for long periods, and it’s common for bearings to need checking/adjustment at the start of each boating season.
Signs of Incorrect Adjustment:
- Excessive wheel end play or wobble
- Grinding or humming noises when towing
- Heat at the hub after a short drive
- Uneven or premature tire wear

⚠️ If bearings are too tight → they overheat, causing grease breakdown, scoring, or even bearing failure.
⚠️ If bearings are too loose → the hub wobbles, leading to poor tracking, seal leaks, and accelerated wear and could lead to hub/wheel separation from the trailer.

Proper adjustment ensures the hub spins freely with minimal play, extending bearing life and keeping your trailer safe on the road.

How to Adjust Boat Trailer Bearings (Without Repacking)

1. Raise and Secure the Trailer

Park on level ground, chock the wheels, and raise the trailer with a jack.
Support with jack stands for safety.

2. Remove Cotter Pin / Tang Washer

Take off the dust cap.
Remove the cotter pin or bend the tang washer tab away from the castle nut.

3. Seat the Bearings

Tighten the castle nut while rotating the hub/wheel.
Apply firm torque (50 ft lbs.) to fully seat the bearings into their races. It is not required to use a torque wrench.
Rotate the hub while applying approximately 50 ft. lbs of torque to the spindle nut. This translates into a full hand pressure load with a 12″ long wrench. This “seats” the bearings.

4. Back Off the Castle Nut

Loosen the nut about 1/6 to 1/4 turn to remove the torque applied. Do not rotate the hub.
The goal is no drag but no looseness.

5. Secure the Nut

Tighten the spindle nut until snug, backing off only enough to align the nut slot with the cotter pin hole (or tang washer tab).
Insert cotter pin and bend, or re-bend tang washer tab.
Replace the dust cap.

6. Check End Play

Rock the hub or wheel by hand.
You should feel just perceptible play (typically .001″–.005″).
Too tight = overheating risk; too loose = wobble and wear.

7. Final Check

Spin the wheel: it should rotate freely without binding.
Tug the wheel side to side: very slight play is acceptable, but no clunking.

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Technical Service Bulletin-Bearing Adjustment