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BR’s most successful DMU?

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delt1c

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I'm sure there was a 90mph variant of these which ran Paddington-Banbury services on introduction.
They were chronically unreliable and perpetuated the cramped WR 4-a-side compartment format.
They were quickly withdrawn.

156s for me. It still cheers me up to see one turning up instead of a 150 or Pacer.
Go anywhere, reasonably comfortable and a smooth ride, good view out, highly reliable, still going strong.
158s were problem children at the start (the last stock built before BREL was sold to ABB).
For me they are too cramped to have an inter-city ambience, though the recent ATW upgrade was nicely done.
I seemed to travel on a lot of Derby 108s in the early days in the north-west, far better than the push-pull steam they replaced.
But really most of the 1st generation were rubbish commuter trains and were put on unsuitable long-distance services (eg Manchester-Holyhead), because BR had run out of money to buy proper long-distance DMUs.
Not many votes for the Turbos I see, but they were a great improvement on the high-density and fume-ridden Thames 116s they replaced.
I think you will find that the Turbos replaced 117's which went on to replace many other classes on other regions.
 
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Spartacus

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I’d go 150 or 156. Major thing letting down the 158 is the oven like conditions frequently experienced in hot weather, and to a letter degree the original toilet flush which was prone to leaving any sticky turn left in a dry pan; not good when combined with a hot day! The 158s had quite a protracted introduction too.
 

yorksrob

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I’d go 150 or 156. Major thing letting down the 158 is the oven like conditions frequently experienced in hot weather, and to a letter degree the original toilet flush which was prone to leaving any sticky turn left in a dry pan; not good when combined with a hot day! The 158s had quite a protracted introduction too.

Yes, the original high-tec toilets were a drawback for the 158's - weak flushes, weak hand driers, dodgy doors.

One could have the 156 as a good low tec alternative, however I believe their original seats weren't as good.
 

hexagon789

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One could have the 156 as a good low tec alternative, however I believe their original seats weren't as good.

In my many years travelling on original seat ScotRail 156s I never thought they were uncomfortable, indeed now most have been reseated the old seats seem much comfier!
 

py_megapixel

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I’d go 150 or 156. Major thing letting down the 158 is the oven like conditions frequently experienced in hot weather, and to a letter degree the original toilet flush which was prone to leaving any sticky turn left in a dry pan;
At introduction the 158s were meant to have air con weren't they? It is very ineffective nowadays because it was designed for CFC refrigerants which are now illegal, but it's there in theory.
 

yorksrob

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In my many years travelling on original seat ScotRail 156s I never thought they were uncomfortable, indeed now most have been reseated the old seats seem much comfier!

That's a fair point. I say that in comparison to the original 158 seats and those in the refurbished ones on Northern (even though Northern inexplicably seem intent on replacing these with ironing boards).
 

ac6000cw

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At introduction the 158s were meant to have air con weren't they?

They were all built with air con (as far as I know) - they were meant to have an 'InterCity' ambiance (which is also reflected in the end door only configuration).

Of the Mk1 BR DMUs, my favourites were probably the Met-Cam 101's and the ex-WR 'Cross-Country' units, although the ride on CWR at speed was poor on all of them. Of the 2nd generation, the 156s (I particularly dislike the 150s - I find the interior ambiance awful, I'd rather ride in a 153 than those).

(I suspect if you ran a Mk1 DMU on a twisty bit of CWR at speed today with a load of passengers who hadn't experienced them before, they'd probably wonder if it was a) about to derail as the bogies hunted from side-to-side and b) about to fall apart as everything was vibrating so loudly inside...)
 
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hexagon789

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At introduction the 158s were meant to have air con weren't they? It is very ineffective nowadays because it was designed for CFC refrigerants which are now illegal, but it's there in theory.

They all did, the systems they now have vary wildly in effectiveness
 

hexagon789

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That's a fair point. I say that in comparison to the original 158 seats and those in the refurbished ones on Northern (even though Northern inexplicably seem intent on replacing these with ironing boards).

I know they are different types of seat but to me the original 156 and 158 seats are about the same comfort-wise
 

185

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Either 156 or 158.

158 for build quality, comfort, passenger ride, speed, reliability, driver & guard operating facilities (relative to when it was built).

156 for durability... in winter rescuing other failed trains with them, five hours in a snowdrift on the S&C - they just keep going, can see why Scotrail use them on their Obans & FW.
 

py_megapixel

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Of the 2nd generation, the 156s (I particularly dislike the 150s - I find the interior ambiance awful, I'd rather ride in a 153 than those).
The 156 interior ambiance is an interesting one, because I think that recent refurbishments of them have actually made them worse. I am particularly talking about Northern here; in the Serco-Abellio they were rather nice and I quite liked them; despite the seating moquette being an eyesore in my opinion, there was some nice wood panelling (or maybe it was just a different colour of plastic, can't remeber), the lighting wasn't too bright and it generally felt comfortable. Arriva, on the other hand, have just painted the entire thing white, inside and out, and installed the brightest LED lighting known to man. It's more like an operating theatre than a regional train service. And don't even get me started on the passenger information system...

I have to agree with you about the 150s though; before their recent refurb they were dingy and felt falling-apart, now they feel like an operating theatre, just like the 156s. With the same horrid PIS and the bonus of being sat near to the doors so there are draughts and they slam every time a fast train comes past.

I mean, surely some diffusers for the lights wouldn't have been so much extra expense?
 
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Spartacus

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At introduction the 158s were meant to have air con weren't they? It is very ineffective nowadays because it was designed for CFC refrigerants which are now illegal, but it's there in theory.

Yeah, though if maintained and topped up regularly they do tend to work well, but it needs a lot more work than originally required. One of the big issues is a tendency for the air-con to go into heating mode instead of cooling if it’s still working/on when the windows are opened due to the sensors getting a false reading due to their location.

Speaking of seats, I always thought the original 158 seats had a tendency to go ‘flat’ very quickly, giving you the feeling of sitting in the bucket frame with just fabric covering it, worse than any ‘ironing board’ seat. I remember opting for the luggage space over one of those on a trip over to Manchester once!
 

Cowley

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Class 121s, can't argue with 57 years service!
I mean that’s a pretty good shout to be honest.
I have a feeling that some of the second gen DMUs will be around for a good few years to come mind, although 57 years will take some beating.
 

hexagon789

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Class 121s, can't argue with 57 years service!

Except that for passenger use it wasn't continous, there being a break from 2001 when Silverlink finished with them until Chiltern commenced using a bubble on the Aylesbury-Princes Risborough in 2003. 101s however had continual service 1956-2004.
 

AM9

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I agree they were probably not the right thing to have ordered. I remember reading an article in a magazine of the period which expressed concern at the 70mph top speed! I'm not sure they were that underpowered 6.2hp per ton for an 8-car set is pretty good for the time and would've been plenty for the flat GWML.
Having grown up in suburban Essex, there was little opportunity to ride DMUS, and my multiple unit of choice was the 309. However I was aware of the 123s (and 124s) through their entries in Ian Allen books and can imagine that they had many of the passenger benefits of the 309s. As has been mentioned by others, the inadequate performance must have been quite frustrating, especially on GW metals as linespeed limits wouldn't be an issue for most express services. A hp/tonne figure of 6.2 is misleading because of the meaningless way that diesel trains are rated, the 309s were only 6.8 hp/tonne but that was at the axle and nearly always available.
 

hexagon789

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Having grown up in suburban Essex, there was little opportunity to ride DMUS, and my multiple unit of choice was the 309. However I was aware of the 123s (and 124s) through their entries in Ian Allen books and can imagine that they had many of the passenger benefits of the 309s. As has been mentioned by others, the inadequate performance must have been quite frustrating, especially on GW metals as linespeed limits wouldn't be an issue for most express services. A hp/tonne figure of 6.2 is misleading because of the meaningless way that diesel trains are rated, the 309s were only 6.8 hp/tonne but that was at the axle and nearly always available.

Trouble is I've no idea how you calculate the power-at-rail for mechanical transmission. I know electric transmission was generally quoted as 81% efficient at maximum, hydraulic a bit less but mechanical doesn't get a mention as such.

Even allowing for electric transmission being perhaps more efficient (?), the 123s of would say still had more power for traction compared to their weight than the Blue Pullmans. If you take the traction motor continous rating as the BP's power-at-rail, the WR sets had only about 4.3hp per ton. Would transmission losses reduce even a derated 123 to as low
 

birchesgreen

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Except that for passenger use it wasn't continous, there being a break from 2001 when Silverlink finished with them until Chiltern commenced using a bubble on the Aylesbury-Princes Risborough in 2003. 101s however had continual service 1956-2004.

Class 121 still had longer service life though the Class 101's 48 years is certainly very impressive. I suspect the Class 150 will be the eventual winner for longevity though.
 

AM9

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Trouble is I've no idea how you calculate the power-at-rail for mechanical transmission. I know electric transmission was generally quoted as 81% efficient at maximum, hydraulic a bit less but mechanical doesn't get a mention as such.

Even allowing for electric transmission being perhaps more efficient (?), the 123s of would say still had more power for traction compared to their weight than the Blue Pullmans. If you take the traction motor continous rating as the BP's power-at-rail, the WR sets had only about 4.3hp per ton. Would transmission losses reduce even a derated 123 to as low
It's not just the shaft power less the transmission losses, (gearbox or hydraulic converter, +cardan shafts+final drive) that should be considered. The other issue is that even the best diesel engines have power outputs that vary greatly across the working rotational speeds, (as does the equally important torque availability), and that power is also quite dependent on engine temperature, inlet air temperature and maintenance state.
Most traction motors have a much more consistent power output to a final nose-hung pinion drive/quill drive, even in the series DC types that are involved here.

Edit: Ironically, the Leyland engines were later fitted to the class 115 DMUs for whose service duty they were much more suited.
 
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hexagon789

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It's not just the shaft power less the transmission losses, (gearbox or hydraulic converter, +cardan shafts+final drive) that should be considered. The other issue is that even the best diesel engines have power outputs that vary greatly across the working rotational speeds, (as does the equally important torque availability), and that power is also quite dependent on engine temperature, inlet air temperature and maintenance state.
Most traction motors have a much more consistent power output to a final nose-hung pinion drive/quill drive, even in the series DC types that are involved here.

Edit: Ironically, the Leyland engines were later fitted to the class 115 DMUs whose service duty they were much more suited.

The only thing I could find for diesel-mechanical was that the Danish IC3 units are supposedly 95% efficient in terms of transmission losses when they were fitted with a new gearbox replacing the original.
 

hexagon789

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Class 121 still had longer service life though the Class 101's 48 years is certainly very impressive. I suspect the Class 150 will be the eventual winner for longevity though.

Not so sure about 150s myself, still a way to go to their half-century
 

LowLevel

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156 for me - a bit noisy and draughty particularly since the internal doors were removed.

But you can fill them with luggage all day long, apart from the doors sticking they tend to just keep going. Great medium distance Regional trains. I've only ever failed outright with one once when the door interlocking had an electrical fault.

158 could have been a lot better than it was. The right ideas but 5 or 6 years too early for them to be implemented reliably. Everything tech wise on them doesn't work properly. The internal partion doors when they go on the blink are an all day job to take to bits. The air con has been useless for 30 years and while some attempts have been made no one has really sorted it. The toilets and vanity units are crap and prone to appalling smells. The door systems are temperamental both electrically and mechanically. They're underpowered. They leak where the GRP vehicle ends meet the main body of the vehicle. The cabs are like greenhouses. They have the most ridiculous design of thermostat and stink of diesel fumes, the 1980s micropack for controlling the air con is about as user friendly as a video recorder of the same era and when it is playing up drives the driver mad constantly banging in and out of one state or another. The tilt profile renders the overhead racks largely useless and TOCs have a habit of shrinking the ground level stacks to get more seats in so there is little luggage space. As designed the bike space could hardly squeeze a bike into it.

I could go on - I've spent very many miles on 158s in my working life and if you get a rare good unit all around they aren't bad - until the train gets busy when their shortcomings become obvious.
 

Richard Scott

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The only thing I could find for diesel-mechanical was that the Danish IC3 units are supposedly 95% efficient in terms of transmission losses when they were fitted with a new gearbox replacing the original.
Think if you can get the gearbox to 'lock up' at higher speeds so effectively you have a direct drive to the final drive it would be highly efficient.
 

hexagon789

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Think if you can get the gearbox to 'lock up' at higher speeds so effectively you have a direct drive to the final drive it would be highly efficient.

I thinks that's how most mechanical and hydraulic transmissions work, they go into direct drive in top gear/higher speeds?
 

Richard Scott

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I thinks that's how most mechanical and hydraulic transmissions work, they go into direct drive in top gear/higher speeds?
Think some still drive through a torque converter or fluid flywheel, which still causes loses, if this is locked up too so a complete direct drive (think some automotive transmissions may do it) then no frictional loss from that part of transmission.
 

hexagon789

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Think some still drive through a torque converter or fluid flywheel, which still causes loses, if this is locked up too so a complete direct drive (think some automotive transmissions may do it) then no frictional loss from that part of transmission.

I assumed "lock-up" was akin to direct drive, presumably that only applies with fully mechanical gearboxes then
 
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