I doubt the vibration you felt was from the sides of the floats, but maybe.
We once acquired several sets of brand new never used EDO 3430 floats from military. Problem was they all had rigging for the C 195. Spreader bars were longer than 185 rigging, but no problem. But rear vertical struts were much longer than those for a 185.
So, figure out the ideal length for aft struts, cut to that length, and off you go.
At one point, I was in need of a replacement 185. Our Aircraft folks said they’d have one on floats by the time I got there. So, next morning I jumped a jet to ANC, and walked to our maint. base on Lake Hood.
Out front sat my new ride, on a set of those surplus floats. It sure looked nose high sitting there, but I assumed that was because the plane was tied in to the slip.
Plane needed a maint test flight after annual and float install. So off I went.
Lift off from Hood and OMG, what the hey is that vibration? Power to idle and plop back in water. Taxi to maint. Short conversation with Management, who concluded Weenie Pilot type don’t know shit, so one of THEIR Super Pilots will now conduct a proper post maintenance flight.
Like a dumb shit, I plop down in right seat to observe.
Super Pilot gets airborne and sits there, as this thing shakes like a dog shitting peach pits……and I am speechless. He turns to me and says “Seems okay to me.”
I asked him what our airspeed was. “Holy shit, I can’t read ANY instruments!” Vibrating that bad. We are now over Cook Inlet, and he’s thinking about landing there.
“I have the controls!” Call LHD Tower and tell them we’re returning.
Turns out the new guys in our maint shop had cut the aft struts off something like 2 inches too much. They got out the “old guy’s notes” and cut a new set of struts.
Problem solved. We figured those vibrations were from prop pulses hitting the aft decks of the flat top floats.
Turned out to be a great rig once they got the aft struts right…..they actually were a couple inches shorter than standard 185 struts. That thing ripped out of the water.
MTV