A 40 meter 1/4 wavelength vertical with 1/4 wavelength elevated radials should resonant on 40 meters and close to 15 meters. There should not be a resonance on 17 meters. However it should work OK on 17 meters if you solve the SWR problem.
There is a way to make a vertical resonate on both 40 and 17 meters, although it's a little tricky. I hate to recommend this because of the common mode problem. It's a little like creating a vertical version of an OCF antenna. That would be to shorten the radials and lengthen the vertical element, something like six 25 ft wire radials and a 38 ft, 1 inch diameter vertical element. Maybe that is what you had. That should work OK on both bands. You will need a good feedline choke to keep the common mode currents off the feedline. Another combination that works is four 25 ft radials and a 37 ft vertical element, all made from wire. If the vertical element is not wire (maybe the vertical is a mast, you will have to modify both of those dimensions).
A 40 meter delta loop won't have a resonance on 17 meters, the SWR will be very high. It should resonate close to even multiples of the fundamental, i.e., 40M, 20M, 15M, etc. Worse yet, with horizontal polarization most of the signal will be directed up at a very high angle on 17 meters. You could feed it with ladder line in the middle of a vertical side and that would be OK on 17 meters.
Jerry where is the best place to put the balun on a 40m deltaloop on the top or in de corner downstairs??