The tires on a boat trailer are supposed to be perfectly parallel to one another as they travel down the highway. Makers of boat trailer axles weld the spindles to the axle using perfectly aligned jigs to ensure the wheels are properly aligned when the trailer is new. A boat trailer can get out of alignment when an accident occurs or from hard bouncing when the trailer navigates down extremely rough roads, resulting in the axle being bent out of shape. The only way to correct the problem is to bend it back into its original position.
Hold the end of a tape measure on the inside of one of the trailer tires at the outer edge of the wheel rim as close to the front of the trailer as possible.
Stretch the tape to the inside of the wheel on the other side of the trailer, again to the outer edge of the wheel rim as close to the front of the trailer as possible and make note of the distance between the two rims.
Measure the distance between the insides of the wheel rims as you did in the first two steps, but this time at a position as close to the rear of the trailer as possible. The measurements need to be identical and, if they aren't, the measurements will reveal which direction to bend the axle to bring the wheels into alignment.
Fasten a log chain securely around the axle and spring bracket on each end of the axle, with enough droop in the chain to allow a hydraulic bottle jack to be inserted between the chain and the axle at the axle's midpoint.
Position a 2-foot long two-by-six board between the bottom of the jack and the axle to spread the force of the jack over a greater distance; then position the chain across the top of the jack and lever the jack until the chain gets tight. This step will be infinitely easier with a helper.
Continue levering the jack to pull the chain tighter, eventually bending the axle a little. Bend the axle incrementally instead of trying to do the bend all at one time and risk bending it too far. Bend it a little, let off the pressure, measure the rim to rim spacing to see if it's correct or needs a bit more of a bend. When the measurements on the forward part of the rim and the back side of the rim are identical, the trailer is aligned.
- This procedure is designed to make only slight adjustments to an axle. If the original damage is extensive, resulting in the front and back measurements being several inches different, you'd be better off installing a new axle than repairing the damaged one.
- This alignment process will adjust the tow-in or tow-out of a trailer's tire. If the axle is bent up or down, the camber of the tire (the amount they lean in or out), use the same process to make that adjustment.
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