i know that harley started making the softail in 84 but what im not sure what years if any they used a round backbone rather than a square one. im looking to buy one that has a round backbone if possible. any help in the facts department is appreciated.

 

Tom84fxst knows a ton about these bikes, he is on the Evo forum a lot as well.

 

Here is a picture of a 1984 FXST frame. In 1986 they changed a couple things. Got rid of the flame cut curved piece on each side that bridges the upper and lower frame in the rear. That was replaced with a forging. That piece had smaller holes for the rear struts, so the bolts holding the struts/struts are slightly different after 85. They also changed the transmission mounting pad too since they went to a 5 speed for 86.

After that point they didn't make any changes I can find (aside from eliminating the braket that holds the rear shock reservoirs on the early models) until they came out with the twin cam in 99. The rear down tube was eliminated and the whole frame was changed and stiffened.

Hope that helps, but to answer your question directly, any Evo softail should fit the bill. The backbone isn't a perfectly straight line though, (like a chopper frame typically would be) they basically hacked the back half of the FX frame and welded on the softail parts.