Diesel Mechanical Multiple Unit performance

[jp4712]

AEC, Leyland and Gardner all had vertical and horizontal engines available by the mid 1950s. It so happens that one of my preserved buses has a vertical AEC engine, and the other has a horizontal Gardner 6HLX.

I suspect that the reason why only AECs and Leylands were fitted to DMUs was that the standard truck/bus engine made by Gardner, designated 6HLW in horizontal form, was underpowered compared to the AEC and Leyland (although it had other advantages such as low fuel consumption and unrivalled reliability). The more powerful Gardner 6LX and 6HLX didn't become available until around 1960, long after most first generation DMUs were built.

Now, the thing about Gardner engines were that they were modular - 4LW, 6LW, 8LW, even 5LW etc - so BR could have had 8HLW engines for more power. But that would have given problems of fitting, as the 8-cylinder Gardner was much longer than a six-cylinder equivalent.

Gardner also made a separate line, called the L3 series, also modular and originally intended for marine applications to be a real low speed 'slogger' with bags of torque. So BR fitted the 8L3 Gardner engine to classes 03, 04 and 05 (maybe others too) as the length of engine with eight cylinders wasn't a problem and a low-speed high-torque 'slogger' was ideal for shunting.

There's one other possible reason why Gardner engines weren't fitted to first generation DMUs: Hugh Gardner. Hugh picked his customers and if he didn't like you, you couldn't have them - it was as simple as that! It's possible that Gardner simply declined to supply BR, although maybe not given the supply of 8L3 engines for shunters. I do know that Hugh was very conservative, for example he prevented experiments with turbochargers until the day he retired, and Gardner may have been reluctant to risk its hard-won reputation for reliability by exposing their engines to this new usage.

Anyway, back on topic: in the mid 1980s I often travelled from Birchwood (near Warrington) to Manchester Oxford Road via the CLC, and if the service was due to stop at Irlam then there'd be zero chance of reaching top gear on the climb from there to the Manchester Ship Canal bridge. I play train simulators a lot, and I do agree that the thing they have in common is being over-powered compared to my recollections.

 

[lostwin(m)]

In my bashing days, probably ‘84, I caught something fairly tasty out of BNS, but had to bail at Gloucester - being the limit of my Rover ticket. The only way back was on an all stops unit, a 3 car perhaps.

We trundled interminably, eventually getting to the Bromsgrove stop and a signal then checked us at the foot of the Lickey. Once released the driver gave it the full beans, by the top we must have been doing at least 50mph, with no sign of the acceleration tailing off.

Mind you, the 4000hp shove up our backside from the pair of 37’s may have had something to do with it

The only time I had the bankers up the Lickey.

 

[Merle Haggard]

In the 1960s, Accrington shed was the home to the exciting 'power twin' Cravens 2 car sets. They had a very raucous exhaust and on visits to Newton Heath shed from Victoria they certainly seem to have a lot of 'go' up the bank; they were also a common sight at Preston, leaving the East Lancs side eastwards with great gusto.
Of course, being Cravens, the sensation of rapid acceleration and high speed was accentuated by the high amplitude vibration of everything metal - luggage racks, window-vents, etc..
But, looking at books about d.m.u. there's the suggestion that, although both cars were powered, there was only one engine in each, making my idea of them being a GT dmu a misunderstanding.
Does anyone know the origins? They were particularly short-lived, even compared to other Cravens sets.

 

[Bevan Price]

In the 1960s, Accrington shed was the home to the exciting 'power twin' Cravens 2 car sets. They had a very raucous exhaust and on visits to Newton Heath shed from Victoria they certainly seem to have a lot of 'go' up the bank; they were also a common sight at Preston, leaving the East Lancs side eastwards with great gusto.
Of course, being Cravens, the sensation of rapid acceleration and high speed was accentuated by the high amplitude vibration of everything metal - luggage racks, window-vents, etc..
But, looking at books about d.m.u. there's the suggestion that, although both cars were powered, there was only one engine in each, making my idea of them being a GT dmu a misunderstanding.
Does anyone know the origins? They were particularly short-lived, even compared to other Cravens sets.

The Cravens units with Rolls Royce engines were somewhat unreliable, and one or two "self-ignited". Unlike earlier Cravens units, they had almost solved the "rattling components" problem. However, following the numerous line closures and service reductions (Marples/Beeching, etc.), there was a surplus of dmus, and non-standard or problematic classes were amongst the first to be withdrawn.

 

[Merle Haggard]

The Cravens units with Rolls Royce engines were somewhat unreliable, and one or two "self-ignited". Unlike earlier Cravens units, they had almost solved the "rattling components" problem. However, following the numerous line closures and service reductions (Marples/Beeching, etc.), there was a surplus of dmus, and non-standard or problematic classes were amongst the first to be withdrawn.

One of the innovative ideas on the Cravens was for the prop shaft (cardon shaft) to go through a 'tunnel' in the fuel tank. What could go wrong?
I recollect some mishap which, when investigated, seemed to suggest that 9D fitters didn't altogether understand the importance of lubricating U.J.s correctly. At least, after a U.J. has given up, the prop shaft doesn't flail about so much in a Cravens - it's restrained by the fuel tank - initially...

 

[D6130]

The two car Cravens 'power twin' units were delivered in two batches of 25 units, each having a single 238 bhp Rolls-Royce engine in each car. The first batch (TOPS class 112) had standard mechanical transmission and were initially allocated to Speke Junction and Newton Heath depots for local services in the Liverpool and Manchester areas. The second batch (TOPS class 113) had R-R hydraulic transmission and were initially allocated to Accrington depot, whence their acceleration and high power/weight ratio proved invaluable on the 1 in 40 Baxenden Bank (Accrington-Manchester via Bury line) as well as the 1 in 70 gradients either side of Sough Tunnel on the Blackburn-Bolton line. They operated cyclic diagrams which covered - amongst other routes - Manchester Victoria-Bury-Accrington-Colne-Skipton and Skipton-Settle-Appleby-Carlisle local services. For a while in the mid-1960s, some of the hydraulic units - which could be distinguished by their large combined four character headcode and destination displays above the windscreens - worked out of Cricklewood, where they were used on peak hour services to and from Moorgate and on the Gospel Oak-Barking line....before returning to Accrington for their last couple of years' service, being withdrawn in 1969-70 after only ten or eleven years in traffic. When they worked, they were powerful and efficient units but - as has been alluded to upthread - the major design flaw of having the cardan drive shafts passing through an aperture in the fuel tank caused two major fires and several lesser ones. The most serious fire - in the middle of Sough Tunnel - completely destroyed one unit....to the extent that its frames and bodywork were so badly distorted that the remains had to be dragged out of the tunnel and cut up at the lineside. A second unit was damaged beyond repair a short time later after catching fire at Shoe Mill on a Skipton-Manchester Victoria service. (Source: www.railcar.co.uk).

 

[Merle Haggard]

The two car Cravens 'power twin' units were delivered in two batches of 25 units, each having a single 238 bhp Rolls-Royce engine in each car. The first batch (TOPS class 112) had standard mechanical transmission and were initially allocated to Speke Junction and Newton Heath depots for local services in the Liverpool and Manchester areas. The second batch (TOPS class 113) had R-R hydraulic transmission and were initially allocated to Accrington depot, whence their acceleration and high power/weight ratio proved invaluable on the 1 in 40 Baxenden Bank (Accrington-Manchester via Bury line) as well as the 1 in 70 gradients either side of Sough Tunnel on the Blackburn-Bolton line. They operated cyclic diagrams which covered - amongst other routes - Manchester Victoria-Bury-Accrington-Colne-Skipton and Skipton-Settle-Appleby-Carlisle local services. For a while in the mid-1960s, some of the hydraulic units - which could be distinguished by their large combined four character headcode and destination displays above the windscreens - worked out of Cricklewood, where they were used on peak hour services to and from Moorgate and on the Gospel Oak-Barking line....before returning to Accrington for their last couple of years' service, being withdrawn in 1969-70 after only ten or eleven years in traffic. When they worked, they were powerful and efficient units but - as has been alluded to upthread - the major design flaw of having the cardan drive shafts passing through an aperture in the fuel tank caused two major fires and several lesser ones. The most serious fire - in the middle of Sough Tunnel - completely destroyed one unit....to the extent that its frames and bodywork were so badly distorted that the remains had to be dragged out of the tunnel and cut up at the lineside. A second unit was damaged beyond repair a short time later after catching fire at Shoe Mill on a Skipton-Manchester Victoria service. (Source: www.railcar.co.uk).

Thanks, that's really informative. I did travel on some other routes listed (including Skipton - Preston) though my aim was chasing steam and I didn't take as much notice of them as I now wish I had. I do remember it was easy to sit close to the (interior) exhaust to savour the resonance at particular revs.
In the 'railcar' summary, I found a good example of 1960s ameliorating a problem rather than solving it - the 'lower footsteps fitted at one end of each car' after the Sandridge accident are presumably to make it safer to evacuate the car when it catches fire, rather than addressing the primary problem. (I think there was a fatality due to evacuation through a window)

 

[Magdalia]

When they worked, they were powerful and efficient units but - as has been alluded to upthread - the major design flaw of having the cardan drive shafts passing through an aperture in the fuel tank caused two major fires and several lesser ones. The most serious fire - in the middle of Sough Tunnel - completely destroyed one unit....to the extent that its frames and bodywork were so badly distorted that the remains had to be dragged out of the tunnel and cut up at the lineside. A second unit was damaged beyond repair a short time later after catching fire at Shoe Mill on a Skipton-Manchester Victoria service.

There was also a fire at Sandridge, near St Albans, on 12 June 1968, with two fatalities, involving M51726 and M51690.

The Accident Report is here:

https://www.railwaysarchive.co.uk/documents/MoT_Sandridge1968.pdf

Report on a fire that occurred on a Diesel Multiple-Unit Passenger Train on 12th June 1968 at Sandridge near St. Albans​

It includes the following description of the incident:

The fire was caused by a transmission failure resulting from a lack of lubrication in an epicyclic gearbox which seized and was torn away from its mounting. The universal joint at the output side of the gearbox broke and the free end of the cardan shaft, flailing within the tunnel formed by the main fuel tank, ruptured the latter, releasing some 100 gallons of diesel fuel which immediately caught fire. Though the fire did not penetrate the floor of the passenger accommodation, a quantity of smoke found its way into both the seventh and eighth coaches. The exteriors of both vehicles were badly damaged

 

[Grumpy]

If you wanted an "exciting power twin" experience there was little to beat the WR Bubble cars. Nothing to shout about when ambling along branch lines with DTS attached. However when running as single units on the main line they could really shift-300hp for 38 tons.
In the mid 1970's they ran singly on some of the Reading-Bedwyn services. Rapid acceleration between stops then flat out running-noisy/hunting/yawing/bouncing/vibrating/rattling. Almost a theme park experience.

 

[Taunton]

If you wanted an "exciting power twin" experience there was little to beat the WR Bubble cars. Nothing to shout about when ambling along branch lines with DTS attached. However when running as single units on the main line they could really shift-300hp for 38 tons.
In the mid 1970's they ran singly on some of the Reading-Bedwyn services. Rapid acceleration between stops then flat out running-noisy/hunting/yawing/bouncing. Almost a theme park experience.

They were also used, in pairs, on the Plymouth to Saltash local shuttle, which was heavily used before the road bridge opened. Pairs of powered bubble cars, that is, not one with a driving trailer. This was in part because there was a creamery at Saltash, and through the day several workings used to bring GWR 6-wheel milk tankers, a couple at a time, across to Plymouth, where the station pilot assembled them into a longer milk train for London. The power was also handy for nipping onto the single line section across the Royal Albert bridge quickly.

The later Cravens twins described above were of course a BR idea, Cravens were just the contractor who were asked to build them (and got stuck with the notoriety). More power was wanted, so Rolls-Royce 238hp engines instead of the usual 150hp ones, same as on St Pancras to Bedford, except that two such engines fitted between the bogies of the latter, long-frame cars, but not under the shorter low density ones. Never mind, instead of the nicely symmetrical two engines under a power car, plus an unpowered driving trailer, let's put one engine under each car. What could possibly go wrong?

Well, for a start the nice symmetrical balance of the car is upset by just one engine on each. High powered Rolls engines had not been put through mechanical transmission before, only hydraulics. Both in combination led to considerable vibration, and as described before ultimately mechanical failures.

 

[75A]

I remember during the ASLEF Strike in 1982, that some Western Region DMMU's were used on the Brighton mail line running backwards and forwards between Brighton & Victoria, needless to say they couldn't keep time, but I'm sure the people that used them (including me going to a Test Match) were appreciative.

Being a Southern Man I've no idea what units they were other than they usually were on the Reading/Gatwick services via Redhill.

 

[D6130]

Being a Southern Man I've no idea what units they were other than they usually were on the Reading/Gatwick services via Redhill.

Gloucester Railway Carriage & Wagon Company class 119 three car cross-country units, with Derby-designed low-density bodies and - by then disused - buffet counters at one end of the centre trailer car.

 

[75A]

Thank you, certainly the morning one up to Viv was 3, 3 car units which were very noisy and smoky leaving Brighton.

 

[randyrippley]

Gloucester Railway Carriage & Wagon Company class 119 three car cross-country units, with Derby-designed low-density bodies and - by then disused - buffet counters at one end of the centre trailer car.

Swindon designed bodies
Derby cabs

 

[The Crab]

I remember during the ASLEF Strike in 1982, that some Western Region DMMU's were used on the Brighton mail line running backwards and forwards between Brighton & Victoria, needless to say they couldn't keep time, but I'm sure the people that used them (including me going to a Test Match) were appreciative.

Being a Southern Man I've no idea what units they were other than they usually were on the Reading/Gatwick services via Redhill.

Did they have to be double-manned to provide traction knowledge?

 

[Taunton]

Thank you, certainly the morning one up to Viv was 3, 3 car units which were very noisy and smoky leaving Brighton.

If capacity was wanted, and it sounds like it, then I guess Reading depot, which ran them, would have turned out a formation of their Pressed Steel units, which would provide a far higher seat count than the Gloucesters.

Swindon designed bodies
Derby cabs

And, for the Pressed Steel cars, wholly a Derby design, with the drawings sent up, Pressed Steel in Paisley didn't have any railway design capability, but built a lot under subcontract, including these, BR standard Mk1 hauled stock, and a lot of 4-wheel wagons.

 

[Merle Haggard]

And, for the Pressed Steel cars, wholly a Derby design, with the drawings sent up, Pressed Steel in Paisley didn't have any railway design capability, but built a lot under subcontract, including these, BR standard Mk1 hauled stock, and a lot of 4-wheel wagons.

This is something I have often wondered about; when the same design was built at different workshops were all the patterns (for cast items) made by pattern-makers at each works? Or did one work's pattern-makers knock out several copies to send to each works? It's possible that, for large quantity parts, there might be more than one pattern in use at a particular works. Same question arises for the moulds for glass fibre mouldings. I don't know if jigs were used, but same duplication would apply to them

It just seems a massive duplication of effort - not so much in d.m.u. and coaches, but think of the number of different patterns requires to build a G.W. - design '9400', built at several private builders + Swindon.

 

[randyrippley]

Pure conjecture, but somewhere like Pressed Steel was primarily a bodyshell fabrication / erection shop, which had branched into assembling complete coaches. They would have no problem bending and welding steel, but I suspect for castings they would have been dependent on supplies from the BR workshop foundries.
Same with the class 119 - they were said to be essentially the same as the Swindon 120 except for the Derby cab. A lot of castings and components probably came from Swindon. As for the cabs, most references simply describe them as "Derby cabs" or "Derby designed", but I have seen references that the cabs were actually built at Derby. It would be interesting to know the truth.

 

[eastwestdivide]

If capacity was wanted, and it sounds like it, then I guess Reading depot, which ran them, would have turned out a formation of their Pressed Steel units, which would provide a far higher seat count than the Gloucesters

I think the 119s were the standard traction for Reading-Gatwick-Tonbridge services around then, so that Brighton run could possibly have been cobbled togeth from units on hand at Tonbridge/Redhill. Don’t know the details of the dispute - if SR only, then maybe the 117s were needed elsewhere? Just a theory!

 

[Taunton]

Pure conjecture, but somewhere like Pressed Steel was primarily a bodyshell fabrication / erection shop, which had branched into assembling complete coaches. They would have no problem bending and welding steel, but I suspect for castings they would have been dependent on supplies from the BR workshop foundries.
Same with the class 119 - they were said to be essentially the same as the Swindon 120 except for the Derby cab. A lot of castings and components probably came from Swindon. As for the cabs, most references simply describe them as "Derby cabs" or "Derby designed", but I have seen references that the cabs were actually built at Derby. It would be interesting to know the truth.

The Western Region, for whatever reason, seemed to like the Derby cabs, and specified them for all their units built by others, Pressed Steel (as here), Gloucester RCW and Birmingham RCW, the latter two having had their own designs used elsewhere. Only exception was, bizarrely, the units built at Swindon itself.

Gloucester, who built the 119s, had been a longstanding subcontractor to Swindon works, and had previously built the first production run of the GWR streamlined railcars. The Western were very attached to their exact shade of livery, and the chocolate and cream paint was shipped out from Swindon stores to Gloucester for all they built which was so painted.

The regions played a significant part in specifications. A major order was placed with Birmingham RCW for cars for the LMR and NER, all built together, but each region had specified a quite different interior fitout, with not only their own colours but the actual materials used. One asked for timber veneer sidewalls, the other melamine.

 

[75A]

I think the 119s were the standard traction for Reading-Gatwick-Tonbridge services around then, so that Brighton run could possibly have been cobbled togeth from units on hand at Tonbridge/Redhill. Don’t know the details of the dispute - if SR only, then maybe the 117s were needed elsewhere? Just a theory!

No, it was a national dispute about flexible rostering, went on for ages.

 

[Magdalia]

The regions played a significant part in specifications. A major order was placed with Birmingham RCW for cars for the LMR and NER, all built together, but each region had specified a quite different interior fitout, with not only their own colours but the actual materials used. One asked for timber veneer sidewalls, the other melamine.

Plus ca change, plus c'est la meme chose.

 

[randyrippley]

The regions played a significant part in specifications. A major order was placed with Birmingham RCW for cars for the LMR and NER, all built together, but each region had specified a quite different interior fitout, with not only their own colours but the actual materials used. One asked for timber veneer sidewalls, the other melamine.

It wasn't even consistent within the same region: e.g. with the WR 119/120 sets. As built one had (blue?) melamine panelling, one had wood veneer (I can't remember which was which)

 

[Grumpy]

A major order was placed with Birmingham RCW for cars for the LMR and NER, all built together, but each region had specified a quite different interior fitout, with not only their own colours but the actual materials used. One asked for timber veneer sidewalls, the other melamine.

This was the case with the Calder Valley units. They also had different seat covers-I think the NER were a green floral pattern, and the LMR bold stripes.

 

[Welshman]

This was the case with the Calder Valley units. They also had different seat covers-I think the NER were a green floral pattern, and the LMR bold stripes.

Also the LMR ones had curtains in first-class whereas the NER had none.

 

[Taunton]

The regional differences were most apparent, of course, on the Southern, who refused to have anything to do with the mechanical cars, although they later ran into there to quite an extent from the Western. I did read a justification that starting a dmu, if the controls from the drivers' desk failed, needed going trackside to start the engine directly, not practical with third rail electrification. Though that may just have been an excuse.

The Western ignored the common "low density" cars altogether, and devised their own Cross Country units, which were later well regarded elsewhere. The Western were the only one to do "bubble car" single units, and also used suburban-type high density cars on rural routes across the system, including a late build of them by Birmingham RCW for the West Country, which was really the last place you might expect to need them - such cars ran the various local services from Taunton.

The Scottish Region did a variation on the Western's Cross-Country units, with an oddball control arrangement which made them incompatible with anything else, for no particularly apparent reason.

 

[D6130]

The regional differences were most apparent, of course, on the Southern, who refused to have anything to do with the mechanical cars, although they later ran into there to quite an extent from the Western. I did read a justification that starting a dmu, if the controls from the drivers' desk failed, needed going trackside to start the engine directly, not practical with third rail electrification. Though that may just have been an excuse.

The Western ignored the common "low density" cars altogether, and devised their own Cross Country units, which were later well regarded elsewhere. The Western were the only one to do "bubble car" single units, and also used suburban-type high density cars on rural routes across the system, including a late build of them by Birmingham RCW for the West Country, which was really the last place you might expect to need them - such cars ran the various local services from Taunton.

The Scottish Region did a variation on the Western's Cross-Country units, with an oddball control arrangement which made them incompatible with anything else, for no particularly apparent reason.

I have seen the Scottish Swindon-built class 120 cross-country units running in multiple with class 101, 107 and 122 ('bubble car') units. I think you may be confusing them with the class 126 Swindon-built Inter-City units which had a different control system and could not operate in multiple with other classes.

 

[matchmaker]

I have seen the Scottish Swindon-built class 120 cross-country units running in multiple with class 101, 107 and 122 ('bubble car') units. I think you may be confusing them with the class 126 Swindon-built Inter-City units which had a different control system and could not operate in multiple with other classes.

79xxx Edinburgh - Glasgow units, rather than 126 which came later. White Circle control system, instead of Blue Square.

 

[Taunton]

There were apparently two versions of the White Circle control system, so the Edinburgh-Glasgow cars could not couple with the Class 126 Ayrshire cars. It was broadly the same upgrade that happened from the Yellow Diamond to Blue Square mainstream cars, but then applied to the non-standard Scottish control system, so although both coded White Circle they were not compatible. Later they got a few standard Blue Square units as well for the Aberdeen-Inverness line, so that was three separate control systems on the Scottish Swindon-built cars. There was some rebuilding afterwards to make the White Circle cars compatible, in part, but still with some restrictions.

 

[hexagon789]

There were apparently two versions of the White Circle control system, so the Edinburgh-Glasgow cars could not couple with the Class 126 Ayrshire cars. It was broadly the same upgrade that happened from the Yellow Diamond to Blue Square mainstream cars, but then applied to the non-standard Scottish control system, so although both coded White Circle they were not compatible. Later they got a few standard Blue Square units as well for the Aberdeen-Inverness line, so that was three separate control systems on the Scottish Swindon-built cars. There was some rebuilding afterwards to make the White Circle cars compatible, in part, but still with some restrictions.

The 79xxx very soon had a modification made to enable multiple working with what became the Class 126. Incompatibility evidently lasted less than a year, maybe just months, because there are several reports of mixed 79xxx & 126 cars on Ayrshire workings in days before the entire 126 fleet had been delivered and even for some years after as strengthening vehicles in the summer for instance.

There was arguably no need for the 79xxx/126 to be compatible with the 120s, as they never came into contact really.

The only other Class in the area of 120 operations was the 105s based at Kittybrewester and those were Blue Square and frequently operated together with the 120s, even all the way to Inverness at times.

79xxx Edinburgh - Glasgow units, rather than 126 which came later. White Circle control system, instead of Blue Square.

Both 79xxx and 126 were White Circle but the 79xxx system was based on the early Yellow Diamond system, the 126s on the later standard Blue Square system.

Initially the two batches thus had some control and wiring incompatibilities but these were soon resolved and the two batches were used in mixed formations very early on.