What grease should I use on boat trailer wheel bearings, and how often should I repack them?
My boat trailer goes into salt water most weekends, and I don't know what grease the previous owner used. What should I repack the wheel bearings with, and does pumping grease into the bearing caps count as servicing them?
Answer
Use a water-resistant NLGI 2 grease approved for trailer wheel bearings, preferably with an ASTM D4950 GC-LB rating, unless your hub manufacturer specifies otherwise. For conventional serviceable bearings, strip, inspect and repack annually or at the manufacturer's mileage limit, whichever comes first, and service immediately if water gets inside.
Identify the hub and grease
Identify the axle and hub before starting work. Conventional tapered roller bearings can be removed and repacked; sealed cartridge bearings generally need replacing when worn, while oil-filled hubs need their specified oil.
A grease nipple alone does not identify the system. A spring-loaded bearing protector, such as a Bearing Buddy, maintains slight positive pressure inside the hub. A spindle-fed system, such as Dexter E-Z Lube, feeds grease through a drilled spindle. Both still require bearing inspection.
If you cannot identify the existing grease, clean it out during the first service. Colour tells you little: two blue greases can have different thickeners and incompatible formulations.
Choose grease for water and heat
Grease must resist water during launching and cope with road-running temperatures, especially in braked hubs. Check the cartridge or technical data sheet for:
- NLGI 2: the usual consistency for conventional trailer wheel bearings.
- Wheel-bearing approval: an explicit statement that the product suits trailer wheel bearings; GC-LB is a useful performance classification.
- Water resistance and corrosion protection: preferably with boat-trailer or salt-water service specifically listed.
- Compatibility with the hub specification: including any required thickener type or temperature range.
Lithium-complex marine wheel-bearing grease is a common choice. Calcium-sulphonate-complex products also suit immersed bearings if approved for that application. General-purpose chassis grease, stern-gland grease and copper anti-seize are unsuitable substitutes.
Do not mix greases just because both say "marine". When changing products, remove the old grease from the bearings and hub, clean and dry the parts, then use the new grease throughout. Follow the cleaner's instructions. Never spin a bearing with compressed air.
Match servicing to launching conditions
Many conventional trailer axles have a published service interval of 12 months or 12,000 miles, whichever comes first. Check your axle's manual. Frequent immersion, damaged seals and small wheels working hard on long motorway journeys call for closer attention.
- Occasional freshwater launching: annual inspection and repacking is a sensible baseline.
- Regular salt-water launching: inspect through the season as well as servicing annually; shorten the interval if you find moisture or deteriorating seals.
- Unknown service history: repack before the next substantial tow.
- Milky grease, water, rust or gritty rotation: strip the hub promptly rather than adding fresh grease.