When I signed these units there was a pull test as part of the coupling procedure, so I presume that one was done on this train also. However, even assuming that the unit was only formed up in the sidings at Cambridge and this was it's first trip together in multiple, it still got quite a decent distance before coming apart. But it could have been coupled together for quite a lot longer than this as the
modus operandi for these units is to have them in pairs, and I'm not sure to what extent trains are split and reformed at Cambridge. It's certainly not something that seems to happen as a matter of routine. Any train that divides like this will come to a stop automatically and immediately due to the loss of brake continuity.
Linespeed through Harlow is 80mph, but I believe this was a stopping service so probably wouldn't have been going quite that fast.
Not heard of it with 379s but I was on a train which divided three times on a Rugeley - Birmingham service. I got in the 153 which was trailing a 2 car 170 at Landywood. Things went well until Pleck Jn when the brakes went in as were going through the Slow to Fast crossover. The driver obviously knew what had happened so got the 170 onto the Up Main then walked back to drive us back onto it, then we continued until the same thing happened at the top of Soho bank. After some more walking he coupled us together and we proceeded. Just popping out of Monument Lane tunnel it happened again, so he took the 170 down the platform, then walked back again to fetch us.
bit of a shambles really
Not quite the same thing. Cl170s used to suffer from loss of brake continuity due to the connector blocks on the BSI couplers between units pulling apart, but the train itself would not divide. This was particularly the case on tight curves or through pointwork. The only remedy was to unhook and couple up again. It's better now than it was but it's not unheard of for it to happen even now (I've had it three times on ECS moves).