How to Identify Wheel Bearings

Trailer wheel bearings are matched by the numbers stamped on them, not by how they look. Two bearings can look almost identical and be a few thousandths of an inch apart, which is enough to ruin a hub. Here’s how to find the numbers and what to do if they’re gone.

How the parts fit together

Each hub has two tapered roller bearings: a larger inner bearing and a smaller outer bearing. Each one has two parts, the cone (the rollers in their cage) and the cup or race, a steel ring pressed into the hub. A grease seal sits behind the inner bearing, and a dust cap covers the outer one.

Step 1: Take the hub apart

1. Jack up the trailer, support it on a jack stand and remove the wheel.

2. Pry off the dust cap.

3. Remove the cotter pin or retainer, then the spindle nut and washer.

4. Pull the hub toward you. The outer bearing will slide out first.

5. Turn the hub over and gently tap the inner bearing and seal out from the inside.

Step 2: Clean the parts and read the numbers

Wipe off the old grease with a rag or parts cleaner. The bearing number is stamped on the wide face of the cone, and the race number is on the edge of the cup. The inner and outer numbers are different, so write down all four.

These are the sets we see most often in the shop:

Step 3: If the numbers are worn off

Measure the spindle with calipers where each bearing sits. On a common 3,500 lb axle the inner seat is 1-3/8″ and the outer is 1-1/16″. On a 5,200–7,000 lb axle they’re 1-3/4″ and 1-1/4″. Or simply bring the hub and old bearings to the store and we’ll match them on the counter.

Step 4: Inspect before you reuse

Replace a bearing if you see pitting, rust, flat spots on the rollers, or blue or dark straw-colored steel, which means it’s been overheated. Spin it in your hand: it should feel smooth, not gritty.

Always replace the cone and its race together. A new bearing running in an old race wears out fast.

Seals and grease

Replace the grease seal every time the hub comes off. Seals are sized by the spindle and the hub bore, so bring the old one if you can. Pack the bearings fully with fresh grease, and use a marine-grade grease on boat trailers. Plan to inspect and repack bearings at least once a year or every 12,000 miles, and more often if the trailer goes in the water.

Signs a bearing is failing

• Grinding, growling or squealing from a wheel

• One hub much hotter than the others after a drive

• A wheel that wobbles when you rock it top to bottom

• Grease slung onto the inside of the wheel

Get the part or the repair

Shop online for local pickup, or bring the old part to our Port St. Lucie store at 496 SW Voltair Terrace and we’ll help you match it. Not comfortable doing the job yourself? Request a repair and we’ll take care of it, or call us on 772-924-7299.