The LNER Encyclopedia

The mark 3 hauled coaching stock on the Norwich to Liverpool St line appear to have the short swing link type BT10 bogie. It’s not that the links are any shorter than on the long swing link bogie, but that the sideways motion is restricted by – and get this – wire rope attached to the bogie frame!
Maybe that explains why the riding is a little inferior to the GW HST sets. (or it could be the track). Anyway, they’re a step forward from the mark 2’s, especially during hot weather when the mark 2 air con was inclined to pack up.

The Swedey, as it was known to GN blokes, always seemed to be the repository for hand-me-down loco hauled stock, particularly in BR days when money was tight. Certainly the track gets a real bashing on the London side of Colchester so not sure where the blame may lie for poor ride quality but BT10s were good in their day, as they say, now eclipsed for ride quality by those devilish Germans and their Desiros. Hardly surprising as there is about 30 years difference in the designs. Mark 2 vehicles again, were fine in their day but air con was something BR never seemed to master. Thought that when I saw the 1620 Wl'oo - Exeter run in to Basingstoke to take me home last night, several cars had the windows open - a sure sign the air con has packed up. Despite spending millions on the problem, even SWT haven't been entirely successful.