Sometimes a trailer just isn't long enough. A 6-foot trailer won't comfortably carry 8-foot panels of plywood or wallboard or framing lumber or a variety of other objects. It's possible and often easy to "trade up," to replace the short trailer with a longer one, but that may not be an option for every owner of a house, farm, ranch or business. Extending the trailer may be the only choice. It can be done, but requires welding equipment and expertise and stong mechanical skills.
Plan the trailer extension carefully. Don't just add a couple of feet on the end. Trailers must be balanced for safe and efficient operation. Plan to add one foot to the front for every foot of extension on the back. Calculate for new braces and a longer yoke; an extension may alter turning ratios. Examine the existing frame to determine the size and type of metal framing; some trailers use angle iron, some square tubing and some u-channel with one side open.
Remove any flooring and any wiring for tail and brake lights; preserve the wiring for help in installing replacements. Buy new steel to match the existing frame; get extra for waste and added braces. Measure the frame and mark spots to install extensions. Buy some sheet or strap steel to use for gussets or reinforcements on new joints.
Cut the frame at the marked spots with an angle grinder, metal saw or welder's cutting torch. Brace the trailer so removing sections doesn't cause it to tip. Set the removed ends aside. Remove the existing yoke on the front by cutting its welded joints on the frame with an angle grinder or welder's cutting torch.
Measure and cut with the chop saw extension framing. Clamp it in place with welder's clamps and weld to the existing frame on both ends. Cut sheet or strap steel and weld underneath the new joint for extra support. Weld the back extension first. Remove the yoke completely from the front and weld in extensions to that frame, adding supports underneath.
Replace the yoke. If the existing one can be welded back, use it. Make a new yoke or extend the old one so the back ends of the yoke can be welded to the frame just in front of the axle spring hangers. Extend an existing yoke either by replacing the triangular sections or by removing the hitch ball cap and welding on a single extension, then replacing the hitch ball cap. Weld a cross brace or triangular gusset where the bar is added.
Install new flooring and replace the brake and tail light wiring, either by running new wire or by splicing the old with crimp-on connections. Tape any wire splices with electrical tape to seal them.