This is a long way from Cl 304s however - I commuted on them for many years and whilst they had a certain charm I was not sorry to see the back of them. The ride was diabolical with a 'bucking bronco' start and a 'kangaroo' motion once under way. The oscillation could be quite severe if it got into a rythym and would be broken only by crossing points or braking. The Cl 323s were such an improvement and are one of my favourite EMUs - I am pleased that Northern is to retain them and indeed expand the fleet.
The problem with the 304s was only that the leaf springs had been oiled or greased, so the inherent damping had been lost. I liked the AM4s when I commuted on them, the bounciness wan't really a problem.
I have happy memories of AM4s, especially of them slipping around Edge Hill. And of AM10s. And, I think twice, of them running coupled together! This was obviously undesirable as they were differently geared. ...
In the 1970s I worked with the man who did the altered unit diagrams for each week, and on one occasion the aftermath of engineering work had caused a Sunday evening Birmingham - Manchester to be worked by a 304/310 combination, supposedly fully compatible units (I don't know about depot traction knowledge though, that wasn't my patch.)
I was on it with my family and leaving Bham New St and every subsequent station was a nightmare: the 2 units accelerated about half a second apart at each "notching up," so there was a pair of violent longitudinal buffetings over and over again. People still sorting themselves out were falling over, luggage was coming off the racks, it was clearly not an acceptable position.
I told the guard about it when we got off (no through gangways or communication then) and he couldn't understand it ("You mean oscillation?" - "Not really, more like snatching forwards and backwards!")
I told my colleague: he was very interested, and he commented that he had noticed that it was an unusual, but permitted, working and he resolved never to do it again.
p.s so I don't think it was the "gearing" as such, but the different time-delays in the electrical control gear.