When the time comes to replace the axle on a trailer, many people choose to hire a mechanic to take care of the task. With a little knowledge, a few tools and a solid plan, changing a trailer axle is a task easily enough completed by the average do it yourself type person. The first task is to determine the correct size and specification for the replacement axle. Maximum load per axle can be found on the trailer's vehicle identification tag. Along with the weight rating, there are a few measurements to be taken to order the new part. First, the axle length should be measured. If the wheel hubs have already been removed, the overall length from tip to tip can be taken. If the wheel hubs are still in place, the axle should be measured from hub face to hub face. Next, the spring seat center measurement should be taken. If the leaf springs are still installed, the measurement should be taken across the axle, from center to center on the leaf springs. If the springs are not installed, measure from center to center on the spring pads. Using these measurements, a replacement axle can be purchased. It is also a good idea to replace all associated mounting hardware and to recycle the old hardware. If the wheel hubs have not been serviced or replaced recently, show visible signs of wear or damage, or are making noises indicative of worn bearings, this would be a good time to replace them since they have to be removed anyway. With all new parts in hand, it is now time to install the axle. This is best accomplished with the help of another person to help lift and move the axle. Start by loosening the lugs nuts on both tires. Next, raise the trailer using a hydraulic jack, and secure it on jack stands at four points. With the trailer securely resting on the jack stands, remove the tires and set aside. If the trailer is equipped with brakes, disconnect the brake lines and take care to ensure the lines do not get snagged during removal of the axle. If the trailer is equipped with shocks, disconnect the lower shock mount from the axle and set the mounting bolt aside. Inspect the shocks for leaks or worn mounting grommets and replace if they are worn. Remove the wheel hubs and brake hardware and set aside. The axle is secured to the leaf springs with a U-Bolt. Remove the U-Bolts on both ends of the axle, and the axle should be completely disconnected from the trailer. With an assistant on the other end of the axle, lift and move it to the side until completely free of the leaf springs. Once clear of the springs, pull the axle all the way out from under the trailer. Installation of the new axle is simply the reverse of the removal process. Slide the axle under the trailer and position it so the leaf springs rest on the spring seats. Using new hardware, bolt the axle in place, and reconnect the shock absorbers if applicable. Reinstall the wheel hubs and brake assembly, and reconnect the brake lines. Finally, install the wheels and lower the trailer from the jack stands. Be sure to check brakes for proper function, and the job is complete.