What were the safeguards interworking auto + manual 1st gen DMUs?

[Egg Centric]

It is my understanding that it was technically possible for 1st gen DMUs of the same multiple working code to inter operate, even if one was hydraulic transmission and one was mechanical, and indeed this was done for a while. Unfortunately several drivers “forgot”, didn’t change gear, seized the engines of the mechanical rail car and so it was prohibited.

As an occasional driver of the astonishingly good and highly recommend nieche piece of software known as diesel rail car simulator I understand how in an informal devil may care environment this could happen all the time.

However - the railway even back then wasn’t exactly devil may care. I assume this was an obvious risk and there were procedures back then which mostly (but not successfully enough!) avoided this occurring - what were they?

 

[The Chimaera]

If I remember correctly if you had the combination of first gen units you describe you were only allowed to drive from the manual gear change unit so it had to be on the front. If you did drive from the auto change unit the manual gearbox unit would always be stuck in first gear so you would wreck the elliptical gearbox.

 

[Egg Centric]

I cannot say for sure you are incorrect but both in the cab in the simulator and what is described on rail car site it is certainly possible to select gears from the hydraulic transmission unit- gears go 1,2,3,D!

 

[MadMac]

The always informative Railcar site covers this.

 

[Egg Centric]

The always informative Railcar site covers this.

All I see there - and I agree it’s a bloody brilliant site btw - is “There was trouble if the driver had a mechanical set at the back and forgot to change gear - any speed was possible in gear - causing major problems for the gearbox in the mechanical set. Apparently there was a plate in front of the driver which could be lifted to reveal a reminder (something like "Gearbox Stock").”

Perhaps said plate was the entirety of the procedure? But it’s not explicitly stated to be so.

 

[O L Leigh]

I think the point was that the hydraulics were meant to be compatible with mechanical stock to ensure flexibility of utilisation. Therefore any safeguards to prevent that from happening would have been counterproductive. The cab layout was designed as such to permit full multiple working provided that the driver worked the train correctly. As the Railcar website explains, drivers had got habituated to not working with mechanical stock until some were later allocated to the same routes, which is when the problems began. The safeguard then became to change the coupling code to prevent units getting mixed, even though they still remained technically compatible.

How common it was to wreck a mechanical by driving it incorrectly from a hydraulic in multiple is moot. There was the one incident that resulted in the Cravens catching fire as described, but I wouldn't like to say how common it might have been. It appears that multiple working of this type was rare enough anyway, but it could be that this was an isolated incident. I'm sure someone with more knowledge will be along to correct me presently. My point being that if multiple working only resulted in a single incident (although quite a dramatic one) then the procedures set in place to govern this sort of operation could be said to have worked well after all.

But these sorts of issues still happen today. You can still have mixed DMU formations made up of 75mph and 90/100mph units, so it's important to remember that the "slow" unit is in the formation.

There was the infamous story of the Cl153 that had been clocked on it's data recorder at 100mph. The disbelieving managers eventually worked out that it only managed to do this because it had been clipped onto the back of a Cl170. The driver responsible had taken the train over mid-route but hadn't been told about the formation on the handover, so had no idea it was even there and drove the Cl170 to it's permitted maximum. In those instances there aren't even any in-cab reminders, so it's down to the driver to pay attention and do whatever needs to be done not to forget (presumably by writing 75mph in big letters on their job card).

 

[LowLevel]

But these sorts of issues still happen today. You can still have mixed DMU formations made up of 75mph and 90/100mph units, so it's important to remember that the "slow" unit is in the formation.

There was the infamous story of the Cl153 that had been clocked on it's data recorder at 100mph. The disbelieving managers eventually worked out that it only managed to do this because it had been clipped onto the back of a Cl170. The driver responsible had taken the train over mid-route but hadn't been told about the formation on the handover, so had no idea it was even there and drove the Cl170 to it's permitted maximum. In those instances there aren't even any in-cab reminders, so it's down to the driver to pay attention and do whatever needs to be done not to forget (presumably by writing 75mph in big letters on their job card).

The non technical but generally effective solution is that drivers are issued with a pad of small sticky post it notes to write 75 on and stick over the speedo to cover up beyond that point.

I usually stick to the driver drives and the guard guards but in the past I have had cause to ring up and remind them as I've gone banging around rather more quickly than a waddling 153 is comfortable to ride in

 

[Ashley Hill]

If I remember correctly if you had the combination of first gen units you describe you were only allowed to drive from the manual gear change unit so it had to be on the front. If you did drive from the auto change unit the manual gearbox unit would always be stuck in first gear so you would wreck the elliptical gearbox.

The gear selector on a class 127 had the usual 1 to 3 plus D (Drive) gear positions. D if coupled with a mechanical set was the equivalent of 4th gear ie direct drive through the mechanical box. If driven by itself it didn't matter which gear you selected,you just left it there. If you had a mechanical set coupled in multiple behind you, you had to change up down through the gears from the 127 as necessary. 15,27 and 41mph were the change up speeds IIRC.