How to Inspect Boat Trailer Axles, Leaf Springs and Hangers

Park the loaded trailer on flat, hard ground with the tow vehicle attached. Walk around it and look at the stance. Does it sit level side to side? Is one fender much closer to its tire than the other? On a tandem, do both axles look like they carry the same weight? A trailer that leans or sits low on one corner often has a sagged or broken spring, a bent hanger or a worn-out torsion arm on that side.

Tires tell you what the axle is doing. Discover Boating and EZ Loader both point out that tires wearing unevenly, especially on the inside or outside edge, can mean a bent axle or an axle out of alignment, often after a hard hit on a curb or pothole. Look at every tire:

• One edge worn on one tire (or on both tires of one axle): possible bent axle, bent spindle or a spring that has shifted on the axle
• Feathered or scalloped tread: possible alignment or bearing problem
• Even wear on both edges or the center: usually tire pressure, not the axle (see the trailer tires guide)

Don't just replace the tires. New tires on a bent axle will wear the same way.

If you need to see between the springs and the frame, lift the frame (never the springs or axle) with a jack rated for the load, and set jack stands under the frame on both sides. Leave the wheels on the ground where you can, so the springs stay loaded and you can see how they sit. Put on safety glasses before you start scraping rust.

Wire-brush a few spots along the tube, especially near the spring seats and on the bottom where water sits. Tap along it with a small hammer or a screwdriver handle. Solid steel rings or gives a sharp knock. A dull thud, flaking layers, pinholes or a spot that dents when you tap it means the tube is rusting from the inside out.

BoatUS explains why: water trapped inside the axle tube rusts it from within, where you can't see it, and a rusted axle can snap on a pothole. Check whether your axle tube is fully sealed or has drain holes, and if it has drains, make sure they're open so the tube empties after each launch.

Also look for cracks around the spring seats and brackets, and for a tube that looks bent or kinked. Load Rite advises inspecting frames and axles for rust, damage and fractures, and replacing any structural part that has been stressed beyond its intended service.

A note on the bend: many axles have a slight upward bow in the middle on purpose. Dexter calls this camber. It's built in so the wheels stand straight once the axle is loaded. Don't mistake it for damage. A kink, a sharp bend near one end, or a tube that sags downward is different and needs a shop.

Look at each spring from the side and from below. Replace the spring (in pairs, both sides of the axle) if you see:

• A broken or cracked leaf, or a leaf that has slid out of line with the others
• A missing or broken spring clip (the small bands that keep the leaves stacked)
• Rust that has eaten into the steel: thick scale, pitting, or leaves that have thinned at the ends
• Gaps opening between leaves or leaves that look flattened

A spring that has lost its arch and sits nearly flat under load has lost its strength, even if nothing is broken.

Light surface rust on a sound spring is normal on a boat trailer. You can wire-brush it and coat it with a rust inhibitor. Heavy flaking rust between the leaves is not cosmetic. BoatUS notes that on a boat trailer the leaf springs usually rust out long before the frame, so worn-out springs on an older trailer are a sign of age rather than neglect, and replacing them is routine.

The hangers are the brackets welded to the frame that hold the spring ends. Look closely at the welds for cracks or rust lines, and check that each hanger is straight, not bent forward or back. Dexter notes that bent hangers, springs or axle tubes cause bad alignment and bad tire wear. On a tandem, check the equalizer for cracks, wear in its bolt holes and a worn center bushing. A cracked hanger weld is a stop-towing problem and needs a welder or trailer shop.

With the trailer weight on the wheels, put a pry bar between the spring eye and the hanger or shackle, and gently lever back and forth. Watch the bolt. Some movement as the bushing flexes is normal; clunking, a bolt that rattles in an egg-shaped hole, or metal-on-metal contact is not. Signs of wear:

• Holes in the shackle plates or hangers that have worn oval
• Bolts worn thin where they pass through the spring eye
• Nylon or bronze bushings that are cracked, missing or squeezed out
• Shiny wear marks where metal parts have been rubbing

Many trailers have spring bolts with grease fittings. If yours do, grease them as your trailer manual describes. Worn bolts, bushings and shackles are cheap compared with a spring eye that wears through, so replace them as a set when you see wear.

The U-bolts hold the axle on the springs. If they loosen, the axle can shift, which throws the wheels out of line and can let the axle slip off the spring seat. Look for:

• Nuts that are rusted away, missing or backed off
• A gap between the axle and the spring seat, or a shiny line showing the axle has moved
• U-bolts that are stretched, cracked or thinned by rust
• Rust streaks running from the nuts (a sign they've been moving)

Tighten them only to the value in your axle or trailer manual, evenly and in a crisscross pattern. U-bolts that have been run loose, or that have been removed, are usually replaced rather than reused. Don't guess at a torque number.

On a leaf spring trailer, measure from the center of the coupler (or a fixed point on the tongue) to the center of each hub on both sides. On a tandem, also measure hub-to-hub between the front and rear axle on each side. The numbers should match side to side. A difference you can easily see on the tape measure means an axle has shifted on its springs or something is bent. Note the numbers in BoatMend and have a trailer or alignment shop confirm.

If you have a torsion axle, the checks are different:

• Check every bolt and bracket that holds the axle to the frame for tightness, cracks and rust (this is Dexter's one routine suspension check for Torflex)
• Compare the angle of the arms on both sides. An arm that sits noticeably lower than its partner, or a tire that now sits much closer to the fender than it used to, can mean the rubber inside has taken a set or the arm is damaged
• Look for rust-through on the tube and arms, the same as a leaf spring axle

Dexter says not to weld anything to a Torflex axle or move its brackets: the heat damages the rubber inside. Torsion axles can't be rebuilt at home. When they're worn, the whole axle is replaced.

• Light surface rust, everything solid: clean, treat, keep an eye on it.
• Worn shackles, bushings or bolts: replace those parts as a kit, both sides.
• Broken leaf, flattened springs or loose U-bolts that moved the axle: replace springs in pairs and fit new U-bolts.
• Cracked hanger welds, a bent or rust-perforated axle, a bent spindle, or a worn-out torsion axle: trailer shop. Many owners replace the whole axle with a new assembly at this point, often with new hubs and brakes. Order by the axle's capacity, track width, spring centers and spring type, not by guesswork.

Replacement springs must match the originals in capacity and type. A heavier or lighter spring changes ride height and how the load is shared.

"Can I flip the axle to get more ground clearance?" Owners ask this a lot when a skeg or drive scrapes on a steep driveway. Moving a leaf spring axle from under the springs to on top of them (or the reverse) is possible on some axles with the maker's conversion kit, but Dexter notes that it changes the trailer's frame height and center of gravity, which can change how it tows, and its kits can't be used with reinforced spring seats. Turning a drop or cambered axle upside down is a different thing: it would point the built-in camber the wrong way, so don't do it without the axle maker's OK. A taller trailer also sits the boat differently at the ramp, so have a trailer shop confirm any change. Often the simpler answer is to raise the drive or motor to the trailering position your engine manual describes, or to approach the driveway at a gentler angle.

After every salt water launch, rinse the springs, hangers and axle with fresh water, aiming between the leaves and at the spring eyes. Once a season, brush and spray rusty spots with a rust inhibitor. Take a photo of each spring and hanger so you can compare next season, and log the date and anything you replaced in BoatMend.