Upgrading Boat Trailer Hubs: Grease-Through Spindles, Oil Bath, Protectors and Pre-Packed Kits

Be honest about how you use the trailer:

• Launch in salt water, or launch often: a grease-through spindle with a protector-style cap, or a quality oil-bath system you check every trip, is worth the money.
• Long highway trips: hub heat matters most. Any good setup works if it is adjusted right and checked at every fuel stop.
• Trailer sits most of the year: grease is usually the better choice than oil, per BoatUS.
• Old hubs, pitted bearings or a spun race: a complete new hub kit is often cheaper and faster than rebuilding.

Before you buy anything, look for the axle maker's label or stamp (often on the axle tube) and the trailer's certification label (usually on the tongue). Write down the axle make and rated capacity. Then pull one hub (see our wheel bearings guide) and record:

• The numbers stamped on the inner and outer bearings and on the seal
• Whether the spindle end has a grease fitting (grease-through) or is plain
• The wheel bolt pattern (number of studs and their spacing)
• Whether the hub is a plain hub or a hub-drum (trailer with brakes)
• Whether the hub body itself has a grease fitting (some trailer hubs do, often hidden behind the wheel)

The cap must match the spindle. A dust cap with a rubber plug in the middle is made for grease-through spindles: the plug gives the grease gun access to the fitting on the spindle end. On a plain spindle with no fitting, that cap does nothing extra; that's where a spring-loaded bearing protector belongs. Owners mix these up often.

Take photos. Bring the old parts to the store if you can. Bearings and seals are matched sets; "close enough" is how hubs fail.

Clean the spindle and look closely. A new hub will not survive on a bad spindle. Stop and plan an axle repair or replacement (step 11) if you see:

• Scoring or grooves where the bearings sit
• Blue or straw-colored heat marks
• A bearing race welded or worn into the spindle
• Damaged threads for the spindle nut
• A seal surface that is pitted or rusty

Light surface rust that cleans off is usually fine.

Dexter's pre-greased kits are a good example of what a complete kit includes: hub (or hub-drum) with the seal and greased bearings already installed, both E-Z Lube and standard grease caps, spindle hardware and lug nuts. Dexter says having the seal and bearings pre-installed saves about 30 minutes per hub, and its light-duty kits cover axles from 2,200 to 7,000 lb. Whatever brand you buy, confirm:

• It fits your spindle and bearing numbers (or your axle model)
• The bolt pattern matches your wheels
• It is rated for your axle's capacity
• The cap style suits your choice (protector, E-Z Lube cap or oil cap), and a bearing protector matches the hub's cap bore (measure it; protectors come in several diameters, and buyers often order the wrong one)
• For braked trailers, the drum matches your brake size and type

Galvanized or otherwise corrosion-resistant hubs are worth it for salt water.

Dexter warns against mixing lithium, calcium, sodium and barium-complex greases because some do not get along. If you switch grease type, clean out all of the old grease first. Pre-packed kits come filled with the maker's grease; use the same type when you top up, or check with the kit maker.

Switching an oil-bath hub to grease, or the reverse, is more than changing the cap. The seal, cap and sometimes the hub itself are different. The simplest and most reliable path is usually a complete new hub kit of the type you want. If you plan to convert the parts you have, follow the hub maker's conversion instructions and use their seal and cap.

With the trailer safely supported and the old hub off:

1. Wipe the spindle clean and put a light film of the approved grease on the bearing and seal surfaces.
2. Slide the new hub straight on, keeping it square so the seal lip is not damaged on the spindle threads.
3. Install the outer bearing (if it is packed separately), the washer and the nut.

If your new hub is not pre-packed, pack the bearings fully by hand first. Do not just smear grease on the outside.

This is the step that makes or breaks the job. Too tight and the bearings run hot; too loose and the wheel wobbles and the bearings hammer themselves apart. Axle makers use different nuts and retainers, and each has its own procedure (some include a torque value). Follow the instruction sheet that came with the kit or your axle's service manual to the letter.

When you are done the hub should turn smoothly with no roughness, and you should feel no rock when you grab the hub (or tire) at the top and bottom. Lock the nut with a new cotter pin or the retainer the maker specifies. Never "add a bit" past the locking position to make the pin line up.

• Bearing protector: use a hand grease gun and add grease slowly until the spring-loaded piston just starts to move out. Stop there. Overfilling can push grease past the inner seal.
• E-Z Lube or other grease-through spindle: Dexter's method is to remove the rubber plug, seat a manual grease gun fully on the fitting, and pump slowly while turning the hub until clean grease appears around the nozzle; then wipe off the excess and refit the plug. Dexter warns that air-powered guns can push grease past the seal or even dislodge it. On E-Z Lube axles, Dexter also says that if a hub has been removed, the seal must be replaced before you grease it, to keep grease off the brakes.
• Oil-bath: fill with the oil type the hub or axle maker names (Dexter specifies hypoid gear oil) to the level mark on the clear cap, through the fill plug in the hub or the rubber plug in the cap. Wipe the cap clean so you can read it later.

Fit the wheels, snug the lug nuts in a star pattern and torque them to the value in your trailer or axle manual. Lower the trailer. Tow a few miles, stop, and feel each hub with the back of your hand: warm and similar is good. One hub much hotter than the others means stop and recheck adjustment (and brakes on braked trailers). Recheck lug nut torque after the first short drive and again as your trailer maker advises. Look behind each wheel for grease or oil leaking past the seal.

New hubs will not fix:

• A damaged spindle (step 3). On many straight axles the spindle is welded on, so the fix is often a new axle.
• A bent axle or spindle. Uneven or fast tire wear, a trailer that tracks to one side, or a wheel that leans at the top are clues. Note that many trailer axles have a slight built-in arch on purpose so the tires sit flat when loaded; that arch is normal. A shop can measure camber and alignment.
• Heavy rust on the axle tube, spring seats or springs, especially rust that flakes or pits deeply.
• An axle rated too low for the boat, motor, fuel and gear. Weigh the loaded rig and compare with the axle and tire ratings on the trailer label.
• A worn torsion axle (rubber suspension inside the tube) that has sagged so the trailer sits low or bottoms out.

When you order a replacement axle, the supplier will typically ask for the axle's rated capacity, the hub face to hub face width, the spring center to spring center distance, the spring type and the bearing numbers. Measure twice.

Record the date, hub brand, bearing and seal numbers and the grease or oil used in your BoatMend log. Keep the kit instruction sheet with the trailer papers. Then set a reminder to pull and inspect the bearings on your axle maker's schedule, and to check hub heat and cap condition every trip.