Trailer Tongue Jack and Coupler Care: Grease, Adjust and Know When to Replace

• Confirm the ball size stamped on the coupler matches the ball on your hitch. BoatUS warns never to mix sizes: a 2-inch coupler goes only on a 2-inch ball.
• Lower the coupler fully onto the ball, close the latch and put the pin or lock through it.
• Try to lift the tongue with the jack a little: the coupler should stay on the ball. Then lower the weight back onto the hitch.
• Check that the hitch ball's nut is tight with its lock washer. BoatUS points out that many boats are lost when a loose ball lets the trailer separate.
• Raise and swing the jack into its towing position (Step 7), and cross and hook the safety chains (see our safety chain guide).

With the trailer unhitched and the tongue on the jack, look at:

• The socket: cracks, a bent or flared mouth, or a socket worn into an oval shape.
• The latch and its spring: it should snap shut and open without force.
• The mounting bolts to the tongue: tight, not rusted thin, and with nuts in place.
• Rust: surface rust can be cleaned; flaking, pitted or swollen metal around the latch means replacement.

Hose off sand and salt, then scrub the latch area with a wire brush. Let it dry. BoatUS's advice is to always lubricate the moving parts of couplers and balls, and Mercury suggests grease or spray lubricant on the ball, draw bar, hitch pin and receiver to make hookup easier and slow rust and wear.

• Put a light coat of grease inside the socket and on the ball.
• Work light oil or spray lubricant into the latch pivot and spring, and open and close it several times.
• Wipe off the excess so it does not collect grit.

If your trailer has surge brakes, the actuator may also need lubrication at specific points. Discover Boating notes this and says to follow your owner's manual; see our surge brake guide.

BoatUS describes the target: the latch should be tight enough to prevent accidental separation but not so tight that it causes undue friction. With the coupler on the ball and latched:

• If you can lift the coupler and hear or feel it clunk on the ball, it is loose.
• If you have to hammer the latch closed, or it will not release, it is too tight or dirty.

MasterCraft's hookup instructions describe a good latch as one that closes with finger pressure and an audible click, with the pin sliding in easily; if the pin won't go in, the latch isn't fully closed. Never force the handle. If the coupler won't open to unhitch, look for the simple causes first: an oversized or egg-shaped ball, debris in the socket, the tongue jack pushing the coupler up against the ball, or the rig parked facing downhill so the trailer pushes on the hitch. Fix that, then try again.

Many couplers have an adjusting nut (often under the front of the coupler or at the base of the latch) that sets how hard the clamp grips the ball. Turn it in small steps, test, and repeat, following your coupler's instructions. Some couplers, such as Fulton's Fas-Lok, are factory adjusted and have no user adjustment. If the coupler is still loose with the adjustment used up, the socket or ball is worn: replace it.

Look for a ball that is flattened, pitted, rusted or no longer round. A worn ball lets even a good coupler rattle. Make sure the shank nut is tight with its lock washer. If you replace the ball, match both the diameter and the rating to the coupler and trailer, and use the correct shank size for your ball mount.

The weakest link sets your limit. The ball, the ball mount (drawbar), the receiver hitch on the vehicle and the coupler each carry their own stamped or labeled weight rating. Your safe towing weight is the lowest of those numbers, and never more than the tow vehicle's rating. Owners often upgrade the trailer or boat and forget that the old, lower-rated ball is still on the drawbar.

Crank the jack all the way up and down and listen. Grinding, binding or a handle that slips means it needs attention. Typical lubrication points (check your jack's instructions):

• Side-crank jacks have internal gears and bushings. Many have a grease fitting near the crank; give it a few pumps of grease, or remove the top cap and add grease to the gears if your jack is built that way. Crank through full travel to spread it.
• Top-crank jacks usually just need light oil on the screw.
• The handle pivot and the caster wheel axle get light oil.
• The swivel: clean and oil the pivot so it turns freely.

After a salt-water launch, flush the jack, its bushings and the swivel with fresh water and put fresh lubricant on. Some newer jacks are sold as sealed or maintenance-free; follow the maker's instructions for those.

Jack goes underwater at every launch? It's a common complaint on shallow, low-slope ramps, and owners report even good jacks seizing in a single season. What helps: grease the gears under the top cap regularly (not just the factory fill), rinse it every time, and swing it up before backing in if the tongue doesn't need it. Some owners mount the jack farther forward or use a taller jack mounted higher on the tongue so it stays out of the water; that changes the trailer, so check clearance and the jack maker's instructions first.

On a swing-away jack, a spring-loaded pin locks the jack in either the down (working) or up (towing) position. Make sure the pin pops fully into its hole each way. Lock the pin before raising or lowering the tongue, because a jack that swings while loaded can drop the trailer. If the pin is bent, sticky or the spring is weak, replace it. On snap-ring style swivel mounts, check the snap ring is fully seated in its groove.

For towing, the jack should be fully retracted and swung up, or cranked as high as it goes on a fixed jack. Mercury's pre-tow checklist includes confirming the jack is all the way up or locked in its tilted-up position. Remove any drop foot or removable caster before you tow.

Spin the wheel. Replace a wheel that is cracked, flat-spotted, wobbly or seized; a seized caster makes the jack skid and puts side load on it. BoatUS notes single wheels turn more easily on hard pavement and dual wheels roll better on grass. If you park on soft ground, use a pad or board under the wheel or foot so it does not sink.

A wobbly jack is often just loose mounting bolts or U-bolts. Support the tongue on a stand first, then check and tighten the mounting hardware to the spec in the jack's instructions. Check the tongue around the mount for cracks or rust-through.

If the jack is frozen from repeated dunking, soak the screw and gears with penetrating oil, let it sit, then work it gently back and forth in short turns. Do not force it with a cheater bar on the handle. BoatUS suggests spraying corroded mounting bolts with penetrating oil the day before you work on them, and notes that an impact wrench or heat may be needed on old salt-water trailers. If the jack still binds or the tube is rusted through, replace it.

Replace the coupler if it is cracked, bent, worn oval, will not hold adjustment, the latch will not lock, or rust has eaten into the latch or mounting area. Use one with the same ball size and a rating at or above your loaded trailer's weight.

Replace the jack if it grinds or slips under load, the tube is bent or rusted through, the swivel pin will not lock, or it is undersized for your tongue weight. BoatUS notes that swing jacks generally top out at 1,000 to 2,000 pounds of tongue capacity, so heavy boats may need a fixed or powered jack. Measure clearance before switching types: some short tongues do not leave room for a swing jack to fold up.

To swap a jack, block the tongue so no weight is on the jack, remove the old mounting hardware and bolt on the new one as its instructions describe.

Uncoupling safely: MasterCraft says to chock the trailer wheels front and rear before you release the coupler, so the trailer can't roll away. It also warns against moving a surge-brake trailer around by hand on a slope: without the tow vehicle attached, its brakes don't work.