The various types tended to be homebuilt adaptations, starting with the various names - Motor Train, Auto Train, Push-Pull, and possibly others. The LMS used a vacuum pipe control, the Southern used a high level cable control along the carriage tops, and the GWR used a mechanical rotating rod which ran under the centres of the vehicles and loco, and was a right nuisance to connect up. The only auto train at Taunton was the all stations to Castle Cary, withdrawn before my time, but apparently crews often preferred to do it conventionally, and run round at each end, both for ease of coupling and for the controls being very stiff, especially on curves..
The GWR cars were indeed often adaptations of their predecessor steam railmotors, with the engine part removed. In the mid-1950s Swindon built a series of replacements, some of the last GWR-pattern vehicles ever, and had the cheek to paint them chocolate & cream. They were quite soon repainted maroon.
One of the advantages was the avoidance of shunting, particularly at places with restricted space. Both Gloucester to Chalford and Plymouth to Saltash were run like this because of lack of space at the outer terminal. In times before the Tamar road bridge was built the Saltash services were extremely busy, four auto trailers, two either side of the 64xx Pannier Tank, which made the mechanical controls, all connected, even heavier, and not offering the respite of being on the locomotive in one direction.
Lesser auto trains on quiet branches were however notably heavy on the crews; because of the additional responsibilities for the fireman, operating alone on the loco, such as operating the cut-off or the ejector, it was a Passed Fireman role, and the guard I believe also received extra pay for the ticket collecting task. All for often just a small handful of passengers.
The Chalford train served a whole series of stations and halts down to Stonehouse, then ran nonstop to Gloucester where the GWR Swindon line ran parallel for several miles to the LMS Bristol line. This was apparently favoured ground for racing. Noted train timer O S Nock was timing a Bristol to Birmingham express, hauled by a Jubilee, when to his surprise they were slowly but steadily overtaken by a Chalford auto train, propelling carriage first with the loco running in reverse.
I believe some systems had means for the driver in the front car to sound the loco whistle, but the GWR cars had a large pedal-operated gong on the front, same as on their slip coaches, which could be heard from a considerable distance. The driver, right underneath it, must have been deafened by operating it.
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