Is it bad for preserved DMUs to not use certain gears?

[Egg Centric]

It's hard to see how a classic DMU could use 3rd gear on a 25mph line (maybe you could change a little bit early but you've still got to keep it under load from my understanding and change into 4th to coast so how do you do 3rd without speeding?) or now that pacers/sprinters are being preserved there's no chance of them changing into 2nd.

If/when we start preserving 185s then they change into 3rd at over 75!

Never using some gears can't be good for the transmission, right? It's meant to be used. Or are my fears overblown?

 

[LYradial]

As far as I can see all the ones with manual gear change were fitted with an epicyclic gearbox so the input from the engine is always in use, and the output to the gear mounted on the axle is always in use so it is just what happens inside the gearbox that changes.
with an epicyclic box the gears are in use but the speed of rotation changes, slower speed equals more torque.

like an old bus that never goes out of town and rarely exceeds 20 mph, never uses top gear, or even my car that never gets out of third in town.

So no I cannot foresee a problem

 

[Sprinkle]

Apart from like, increased wear on the gears being used (if it isn't a constant mesh gearbox, used in some hydraulics) as long as there's proper oil feed to each component that needs it (which for every gearbox design i can think of that is the case in every gear) and proper maintenance is done, like changing fluids and filters, then i don't think there's any problems really

 

[Richard Scott]

It's hard to see how a classic DMU could use 3rd gear on a 25mph line (maybe you could change a little bit early but you've still got to keep it under load from my understanding and change into 4th to coast so how do you do 3rd without speeding?) or now that pacers/sprinters are being preserved there's no chance of them changing into 2nd.

If/when we start preserving 185s then they change into 3rd at over 75!

Never using some gears can't be good for the transmission, right? It's meant to be used. Or are my fears overblown?

You can get into third for a short period of time.
Biggest problem is bands in gearbox becoming loose so there is a procedure at the end of the day to cycle through all the gears with the engines shut down to sort this out and reduce chance of slipping occurring in that particular gear (that's slipping within the gearbox as loose bands means gear not properly engaged so can slip and not drive as it should, hope that makes sense?).

 

[co-tr-paul]

.....like a semi automatic bus. " Toggling " at start of day to tighten the bands.

 

[jupiter]

There's no problem using 3rd at all. It's not a direct mesh and the road speed doesn't feed back to the crank shaft as in a car. For example you might be doing a depot move that doesn't require any power behind it. Once the unit is moving you can knock it into 3rd with idle power and the unit will keep rolling at the same sort of speed just to overcome friction or a slight gradient say, but the unit doesn't have any torque behind it. Easier to experience than to explain.

I was also taught if you haven't released the brakes enough and you're stopping short in the platform, probably without enough time to lift the brakes sufficiently, you can keep the train rolling to your stopping point with the brakes (lightly) on by shifting from neutral (which would be the 'gear' selected for the final approach phase into the platform) into third and give it a couple of notches of throttle. The lack of torque in 3rd at slow approach speed in the platform means it's basically undetectable to passengers as there's no lurch. Again, easier to demonstrate and experience than to explain.

 

[Egg Centric]

Thanks all - above consensus is reassuring when it comes to classic first gen DMUs. How about sprinters/pacers - just starting to enter preservation now - where it's more complicated and we're talking generally from my understanding a torque converter with lockup - but the lockup now never happening?

 

[Richard Scott]

Thanks all - above consensus is reassuring when it comes to classic first gen DMUs. How about sprinters/pacers - just starting to enter preservation now - where it's more complicated and we're talking generally from my understanding a torque converter with lockup - but the lockup now never happening?

They go into direct drive at around 40mph so no, they wouldn't but then a 153 doing Cardiff Bay branch all day wouldn't either (when it used to be just a shuttle service).

 

[jupiter]

Just further, if you're going up a gentle gradient (1 in 200 say) at linespeed (25mph) in a first generation DMU, you definitely need power but not the nearly-full torque of second at nearly maximum revs. Third is perfectly adequate and appropriate.

 

[Egg Centric]

They go into direct drive at around 40mph so no, they wouldn't but then a 153 doing Cardiff Bay branch all day wouldn't either (when it used to be just a shuttle service).

Sure but it wouldn't do that forever, it would be rotated. This won't be the case for eg a pacer on the Weardale Railway.

It's a pretty obvious point so I'm sure it's been thought about; curious of conclusion.

Just further, if you're going up a gentle gradient (1 in 200 say) at linespeed (25mph) in a first generation DMU, you definitely need power but not the nearly-full torque of second at nearly maximum revs. Third is perfectly adequate and appropriate.

This is interesting - the impression I had, based not really on very much other than instruction manuals more or less saying "change at xmph" was you don't have a great deal of discretion on gears with 1st gen DMUs, in the sense that while the gear is entirely manual there are pretty strict rules about what gear to be in at what speed. Is this a misimpression and aside from the 4th only for freewheeling stipulation so long as you're not going past red line or labouring the engine you have car like freedom while remaining professional?

 

[jupiter]

I'm conscious there are many others way more qualified and experienced than me, but these are my views. I'd say it's a perfectly understandable misimpression.

The manual is absolutely correct for accelerating off to 70mph whether on the flat or up/down a gradient. The gaps between the gears is quite large. What it doesn't go on to cover is where you are restricted in speed (aren't we always?), for example 25mph, where you are right at the top end for one gear and the bottom end of the next. (Max in second is 27mph which should equate to 1800 rpm).

There's no need to be screaming along on the flat at the top end of second at 25mph honking out smoke from your many horizontal bus engines, when you can be happily noodling along in third. Third has plenty of torque to maintain your speed once you're there, even up a reasonable gradient.