Wheel bearings: the failure that ends the trip
A hot hub that has been in cold lake water sucks water in past the seal as it cools. Water in the grease is how bearings rust out, and when a bearing fails it can take the hub and the spindle with it. Repack or replace bearings and seals on a schedule and you'll spend a fraction of what a roadside failure costs.
The warning signs are simple: a hub that is much hotter than the others after a run, grease slung out on the inside of the wheel, a grinding noise, or play when the wheel is rocked side to side with the trailer jacked up.
Brakes, lights and wiring
Trailer brakes and trailer lights both live in a hard place: they go under water at the ramp. Surge brake parts corrode and seize, and brake lines and fittings corrode with them. Light sockets and wiring connections go green and stop working, usually one lamp at a time, until a whole side is out.
Lights and wiring are a safety item on the road and a common fix. The usual fixes are replacing corroded connectors with sealed ones and cleaning up the ground connection — the cause of a surprising number of dim or dead trailer lights.
Bunks, rollers, winch and strap
Bunks and their carpet carry the hull. Rotted boards and worn carpet let the boat ride on bolts and brackets, which marks the hull. Rollers split and seize. The winch strap and its hook take the load every time the boat is pulled up, and a frayed strap is as much of a hazard as a frayed lift cable.
Tires, coupler and safety chains
Trailer tires usually age out before they wear out. Good tread doesn't mean much: after a few seasons parked in the sun a tire can be cracked and dry, and that's the one that lets go at speed. The coupler, its latch and the safety chains are the other quick checks worth doing every spring.
Cracked a member or a bracket on an aluminum trailer? A weld will often fix it, and aluminum welding is part of the same service.
When to do it
The best time is before launch, when the boat is still on it and the trip to the ramp is still ahead. Spring is one of the booked-out seasons, so an early call gets a choice of date.