You can add an axle, springs, mounting brackets, links, and the extra set of wheels and tires for between $200-300. Then you could add some additional angle iron crossmembers for another $150 or so.

What you'll end up with is a trailer with two axles and several extra crossmembers, and all that stuff you added will still be attached to the original frame. Unless the main frame was very overbuilt to begin with, (and utility trailers frames usually aren't), I don't think it's worth it.

Of course there will be several replies saying that if your trailer is rated for 3500 lbs. now, you could easily haul two of your tractors without beefing up a thing....

;-)

If you "add an axle", it should not be just another separate or independent axle assembly attached to the frame. A properly engineered two axle (or more) suspension utilizes "equalizer" brackets (hangers or shackles) between the ends of each pair of springs to help distribute (or "equalize") the load bearing points during movement over uneven surfaces. Equalizing is critical for a number of reasons. Equalizers helps to "spread" the loading between the two (or more) axles so that no single tire (on a given side of trailer) or spring ends up bearing all the load (on that side), due to uneven surfaces. Equalizing also spreads the load to more points on the frame of the trailer which means less bending of the frame on uneven surfaces. If separate, indepenent axles are mounted (without equalizers), it will be the trailer frame that attempts to "equalize the load". You might do a bit of research to see if a "greater capacity" single axle set-up could be used to replace the current one. A heavier single axle with beefier tires and bigger, longer springs would still be more maneuverable than a tandem axle. If it were my decision to replace the lighter axle with a heavier duty single axle, I would reinforce the trailer mainframe side angles (where the spring hangers attach to the frame) with some overlay plates or gusseting (welded to frame at all four points) to strengthen the frame. If you are tempted to use the trailer "as is", remember this: A "static load" of 1,700 Lb. becomes a "huge hammer" when you encounter bumps or dips in the road (or off road) surface. Also, when you go over bumps or dips where only one side of the axle (left or right) is involved, a "tipping effect", or "shock leaning" occurs (causing an increase in the loading of one side for a moment). A similar effect happens when taking a curve or cornering. And what about the occasions when you might want to haul more than just the 1,700 Lb tractor?

I think I might have just got lucky. My youngest son just called and said that he thinks he might have my old trailer sold with only about a $150 loss. I would be very pleased!
So now I'm going to start looking for a good quality 12-14ft trailer tandem axle.
What should I look for?
Any brand suggestions?
I need to stay in the $1,500 price range.
Thanks!

Paint it with Ospho and oily base paint or something like that expensive por before you do much with it.

Utility Trailer Manufacturing is spreading its own sort of reefer madness. Utility Trailer is the largest concern of refrigerated trailers, called reefers, in the US. The consort also produces dry freight trailers, flatbeds, and curtain-sided trailers.

Here is a link that might be useful: Utility trailers

I found this site to be very usefull! Hope this helps

Here is a link that might be useful: us27 motorsports & trailers

PJ makes a nice trailer using Bulldog hitches and Bulldog jacks along with diamond plate aluminum fenders. They also have a spring assisted tailgate (ramp) on certain models.

Worth a look... http://www.pjtrailers.com/