Deltic - Dinosaur or Died too Early?

I remember deltics well of course, even if i had a fleeting relationship to them in their BR service swansong when I was a nipper. Deltics weren't a locomotive you just saw and heard, you felt their power and prescence.

By the last old days of 1980 the deltic reign had ended. All be that ten years after the anticipated life time on  the ECML metals. Just as with the pacific steam locos the deltics replaced, they themselves were superceded . They had become dinosaurs.

Or had they? In reality the fleet got a stay of execution in 1978 and ploughed on with various east coast and the final rather ill suited liverpool - newcastle semi fast diagrams. Rationalised with two of their brethren becoming parts bins,  the rest in reality kept as an exhibition fleet into 1980.

The remarkable thing is that the remaining  locos have survived much longer in preservation: now more than half as long again as their active service wijth BR. The "third age" of the deltics with proffessional management and main line certification.

What then for the alternative history where BR or a private body supported their utility say another decade in service?

Well if privatisation had been happening in the 1970s then gyou can bet that they would have been. A private railway would not have invested in a hundred 56s and the entire class 58. Standardisation versus reliability was a BR mantra , the opposite has been seen across europe and the usa. So the brush type 4 and its under delivered promise and poor reliability would have stopped the later builds. Class 50s would have been sent back to by then GEC leaving deltics, peaks and the more reliable hydraulics to be the main 100mph service providers outside HST diagrams.

Another alterntaive future would have been re-engining.  By 1980 the Ruston Paxman Valenta would have been available in either a v8 at 1650bhp or a v16.  Twin v 12s could maybe fit in a deltic, giving them thus standard units to hst and an RA 6 not to mention 4000 bhp plus!

Maybe other improvements to lub oil and piston / crank systems in the deltic power unit could have made them less smokey and extended service interval to over 3000 hours. Or a turbo version tuned for efficiency.

Whatever the locos when compared to ageing 45s and dodgey engined 47s , deltics were only a tad more smokey and it was burnt oil not spewing diesel and lub. They werent the only relics of the rush to dieselise which were environmentally non PC even by the mid eighties.

Where would they have worked?

If there had been a gap for them to work in an extended lifetime, then it would have been in the west country that they would have thrived. Well into the 1980s there were enough north to south west diagrams with loco change from WCmL or the need for speed from Newcastle or York right through.

However there were also 50 class d400s and seemingly endless ETH peaks in the post oil-sloshing GWR. Not to mention duffs a plenty, one fails send out another until you are down to 47/3s and ice cold trains!

Deltics had higher ETH capacity than 50s and arguably better performance in the 85 to 110 mph range. However it was only the eastern depots, Paxman colchester and donnie works who had the expertise needed in the early 80s in order to keep an ageing fleet going.  Newcastle could then have been a centre for diagrams NE-SW with temporary stabling and driver training only at brum and bristol.

As a small, specialist fleet though there could be a case for remote allocation of servicing.

My own choice would be phasing out 50s over to HGR and including an upgrade to their eth. Thus allocating them to semi fast passengers, over night sleepers and speedlink on the ecml,. Then having 15 deltics allocated to Doncaster with a preserved demo fleet of four to newcstle and haymarket for railtours.

The donne main liners would actually work the west country with extensive drijver training for the wcml to Sw services during the day and the brum and newcastle sleepers at njight. This would be only to 1986 when boilered "bedz" were finally erradicated and enough hsts were released from ecml electrification to free up class 50 to take over any remaining GwR services in their new proven and fully rectified guise.

Full Circle with the Development of the CSVT engine

Proving the internet is a fragmented place not particularly suited to amateur qausi academic research with any comprehensive coverage, I finally complete the full cycle of the history of the CSVT power unit prior to it becoming the RK270 as fitted to the class 56 and 58, and with around 35-75% more power per cylinder than the two 1960s locos in the UK fitted with said beasty, growling power units, the 37 and the 50.

The first two links in this evolutionary tale come from in fact the V8: used in the portugeuse Switcher type locos and the NIR class 101 "thumper" class , where I had heard they were rated up at 1500 hp, but Wiki informs us 1350 the same as the iberian ones. At around the same time, the Aussies had successfully rated the v8 at 1760 hp in the KTM Class 22, which prove to be more reliable than both the Class 50 and the 101s of NIR.

The KTM class 22s were built in the early seventies in Aus' by EE / AEI. The clue here is that they used the CSVT mark III engine. It seems that this engine was not developed in Europe, where the major project was the metric RK instead.

Indeed then the Aussies were pretty keen on EE and developing locos as the power unit technology advanced, seen perfectly with the v 12 going from say the QR class 1270, 1300 (1540 and 1800 hp respc.) up to the 2350 a the same nominal bhp, and there is a quote of taking it to 2550hp ( far short however of the 3300 hp in the class 58) . The RK270 was then first installed in 47 601 at the time, in 1974 thus being built at the same time as the aussie MrkIIIs and probably sharing technology.

The Mrk III engine was the last used in Aus,  I believe from EE and its later GEC who by then owned all of EE and subsidiaries including Rustons and those in Aus. It differed from the predecessors in having gear driven cams and a single stack cumulative exhaust route deliverying to a single, very much larger turbo charger. In the 2350 (at their full rating, not the Tasrail down throttelign to 1750) they sound most like the RK215 engines in fact, spluttering a bit and couging rather more than dubbing, but still recognisable as a thrashy v 12 from Rustons, as in fact is the v12 in the class 58 if you listen carefully or see the video from Tinsley depot, which included footage of them running around with their silencers removed.

The mark II is familiar in the class 37 and class 50, being at ratings of  167 bhp / cylinder in the 50 and 37 292 (2000hp experiment) and 145bhp. Meanwhile the aussies did the KTM at 220 bhp per each of her 8 cylinders, and the eventual 2350 at 195 bhp per cyclinder in her v 12.  This compares to "47 601 " and the class 56 at 3250 hp overall, as 203 hp, and the 47 901  v 12 er then at the massive 275hp. Jumps of 30- 40 horse power then per cylinder in the early seventies and finally the sky was the limit for rustons and the smooth running v 12.

However now the missing gap in my mind, within the evolution from 10000/100001 , the humble class 08, the 20/40 rating and the UK ratings of the CSVT for traction use. A jump of 40hp per cylinder to the Mrk III and then a while went by before the class 58 came along. I sigh a little sigh of relief

The APT: Britains Most Succesful of Failures

Back to another of my chestnuts - the APT - P in particular and a glance at the " E" for experimental predecessor.

The concept of tilting trains dates back some considerable time before even the APT- E (experimental, the single gas turbine version) made the light of day. 1970s technology was adequate for the APT-P , the prototype.

Only we didn't get a prototype, the first of it's type, we got six pre-production types, the class 370.

The crux of the matter lies in this very over ambition. Yes a gas turbine one off had been produced but it was a running laboratory using an already disfavoured power unit supply. Proof of concept was established. However what was needed was a single prototype of the APT-P and not a whole pre-production class.

Why not though, produce a further proof-of-commerciality if you like by having a viable class of APTs running actual passenger specials which reflected the belief in BR management that this was a faite accomplis, as before the HST and the Deltic and electrification had been. In the 1970s though and into the 1980s this arrogance would meet its match in an in patient, road-oriented Magaret Thatcher.

There are major issues with managing a project with six train sets: firstly you have a longer time for delivery and your overall budget is much bigger, despite being lower per unit than a single set. Secondly and most crucially, when you have something go wrong on one set which is serious, then you have to take all the other sets out of service (tests, PR visits and demonstration ADDEXs essentially) . Further to this you then have a very much larger burdon on resources and spare parts when you come to repair the problem or redesign the system.

The tilting system was somewhat problematic however all reports are that eventually this was solved to a level of reliability concordant with operational service. The braking system's design oversights would have been typical "punch list" items for the redesign between and APT- P single electric unit and any pre production run or actual production run (squadron)

Launching the train officially as an operational Faite Accomplis in a January was really just another example of project management not removing elements which could challenge the reliability of the project and its then key PR presentation.

This reflects on poor project management and too much power invested in decision making in BR in my opinion. Today if the railways were still public, or as with HST2 a public-private alliance,  then the project would be subject to tender and also to an expert committee and nost likely the "quantum leap" from the APT-E to the electrified prototype would be managed by a single unit or in fact competing designs.  Subsequently a fleet of pre-scale production models could have been established to introduce the trains such that the flagship services could be accelerated gradually and revenue returns on a 3 hour London-Glasgow, and shorter timings from Manchester, Liverpool and the West Midland towns on the WCML,  services be assessed.

Type threes that never were ... Tantalising possible fantasy locos

Not a lot of people know that most "syphon bashers" actually rated class 33s and hymeks. Given our mutual disrespect for the classes 31, 25 and 27 in particular it may come as a surprise. Type 3s though have to work for a living and have all proven to be capable of running type 4 diagrams. If in 1955 the folly of all the underpowered type 2s had been recognised then we may have had some interesting alternative type 3s.

A fact i did not know is that the 8LDA in the "shreddie" was actually rated at the same per cylinder as the humble class 26, another favourite of syphon bashers as variety on the far north and to annoy 27 bashers. This would mean a potential power output of just under 1700hp in the same locomotive.

How would then an RA5 version of the shreddie with a boiler as a competitor to the EE type 3? AIA configuration. Maybe he same gearing as a shreddie and also eth. Stretch a shreddie for the first of the class and then later orders into the 1960s are roof mounted head code box and a 25 / lion body style? Up at maybe 1685 hp. Given the loco had different field diversion speeds then it could have been a better alternative to the syphon for those draggy 40-50 mph diagrams so loathed by drivers. I can imagine this machine becoming a passenger dedicated dual heat affaire in the late 1970s and working a pile of regional and cross country semi fasts and standing in for duffs on expresses. Scr would have been delighted with them for whl, highland and far north, fife circuit, perth routes and south of glasgow central.

What though if SR had decided on a dual mode version, on an AIA  format with a boiler for non ETH through trains. I rather fancy then a class 34 and 78.  Dual mode deltic with a single PU and 25kv overhead where the other engine used to be?

Another tantalus a diesel electric hymek in co co ? That could have lead to a nice class with uprating possibility for ETH. Or of they had put a decent ventura or valenta in the "Goil" class 31 at over 1600. No matter, there should have been space for the CSVT in there and that would have been then a greater loco than the rather pedestrian accelerating 31.

If Bayer & Peacock were in there then why not NBL ? An MAN v16 or a smaller twin engine type three? A scottish hymek, mini warship completely capable on the route times of the ScR in DE version for north of the border and as an oil slosher.

Finally back to a light weight bobo single engined deltic type 3 to 4. The trouble of the baby deltic was that it was built on a traditional heavy frame chassis rather than the tubular and space frame deltic

Euro Locos gone Loco ?

As I predicted some years ago, dual mode locomotives would become more prominent in r and d, and emerge. They are now the next big thing with rail head transport becoming more cost effective as companies produce scale to compete and road haulage becomes more expensive and slower.

Environmental Politics and economics play as large a part now in shaping the locomotive species as they did in 1955. Now with the emissions vogue for mid to high speed diesel power units things have changed. This means smaller space for the PU more space for scrubbing, but also the possibility for a return to the electro diesel and of course multi engine.

In the 1950's twin engines were chosen due to high power output relative to the available hydraulic and DE transmission systems which were then limited to about 2000 kw at a push in Germany,  and for UK budgets and loading gauges, little over 1000 kw. 

EE worked this one out in relation to getting "3000hp under the bonnet" for sustained 100mph express running, and the WR dedicated to light weight DH power by the early 1950s following the early adventures into heavier 1500-2000hp single engine units. Brush followed suite with the ugly duckling "Hawk" , which could have proven a swan in terms of performance at up to 3000hp compared to the castrated class 47. Even in the ashes of the deltic rose the phoenix of the uk's most successful passenger train, the HST with its high speed Valentas.

First the anglo belgian powered diesel hydraulic to raise eyebrows with its wheel slip free creep lifting enormous coal trains. Then we noticed the reverse, with old locomotives being refurbed sometimes reengined and sent out with new, smaller operators. Suddenly after the predominance of the GM/EMD v 12 two stroke mid speed whiner was under threat by the fragmentation of the industry and the nervousness over buying any loco which may be legislated out of traction wijthin its payback time

Now Bombardier shock us all with not two but four bustly little 750bhp units. This is a modular Traxx loco and they admit to hedging their bets by having a plan for battery replacing one or more power units.

This brings a lot of questions up. Firstly how often do you run on less than all units? Well deltics often ran the aberdeen route north of edinburgh on one unit, pairs of thirty sevens were often switched leading to control only. Another intention from the DB V200, the deltics to the HST was to allow for failure redundancy. This was often the case allowing the service to be completed even on time for the slacker diagrams. DMUs are generally 

Secondly then you have all this on and off, which is bad news however. Larger diesel power units are high compression, long stroke and dual air charged, and the higher speed engines before in time did not respond to idle start stop in traffic.

Thirdly how much power do u really need to start a train? This is a major plus point for the next generation electro diesels which may only need to crawl from the rail head to the overhead AC wires. Here you can haul a thousand tonnes with one of those wee units in the new traxx without a gradient to ply. A class 37 first series once hauled a 1600 tonne dead train in south wales, the lower geared RA 7 version would have maybe done 2000 all be it at less than 20mph.

The next thing is back to longevity versus life cycle. I think it is pretty ridiculous to impose stingent and eventually zero emissions to frieght and express passenger given how many car and lorry journeys they replace. However the road lobby and the percieved need to have clear emissions limits on larger power units across the board means that some locos will maybe only have a 20 years life span and may be reengined or dual moded within that.

Historically rail operators have always tried to run powerunits at longer than manufacturers recommended service intervals and with rarer locomotives like the soveriegn class 60, they attempted to reduce intermidiary "examinations" as they call inspections and filter changes. Given low sales of this new traxx four PU or any other high speed engined loco, then they do not acheive a redundancy in servicing ie there are not enough powerunits spare or ready serviced to feed the small fleet. The pluss side is standard servicing at non rail depots though ,and if it comes to it, a cheaper replacement cost than a single v16 mid or high speed unit.

The future is a bit like 1955 if you ask me , a fragmented approach with some locos.trying hard to fix a political problem, orders being small and a some specialised to country or purpose, deisel electric or hydraulic , flirts with electro diesel, battery and alternatjive combustion. Fifth  generation locos start to sound a lot like first generation fifties ones.

The 37/4s - Why were they built and the Other Rumours at the Time ?

As a thirty seven fan and former addict to haulage by them, I do get de-tractors from time to time ;-)

That is people who question how good they were and why they bothered refurbishing so many of them.

The 37/4 story is the one most at hand here:

The core here is that BR actually had a twenty year old committment to ridding the network of steam heated stock. By the end of steam in 1968, boilers were a complete anachronism but so much of the new coaching stock had been built such that steam could still work them that the phenomenom would tender white whisps and hissing from two tone blue coaches for another 20 years.

For the west highland line this meant that the turning point would be the introduction of the Mrk III sleeper coaches, which had replaced most of the then extensive sleeper services on the main lines,. In addition it wasonly the scottish overnight services retaining steam heat by the early 1980s on the older Mrk I sleepers (Bedz as we called them)

At one point during trials of the stock, Scotrail were quoted in the media as saying the coaches were not suitable and the service was going to be abandoned, but the coaches were in fact pretty suitable for the duty, in particular the air cushioned ride and sound proofing leant themselves to some decent "doss" on the highland and higher speed metals the services ran over to London.

Why did BR not utilise an existing locomotive class with ETH ?

Well the rumour is that Eastfield had at some point asked if they could get the unofficially RA 5 class 33/2s, the slim Jims. However they produce a lower ampage than needed for the sleeper services. Also Eastleigh wanted them for their own purposes of keeping fitters in a job.

The more obvious candidate was the higher ETH rated class 31/4- there is some confusion on how much power these can apply, but realistically a 250 tonne train would be a piece of cake even if they are only sending 1000hp or so down to the wheels. GIven the decision making time of say 1980-82, then in fact these locomotives were very much in use on the cross pennine roots via derby and in the west country where in both cases they had replaced unreliable 1st generation DMU operations. So they were not up for grabs.

Also there is CHris Greene's comments, as the then general manager of the ScR aka Scotrail by then, who did not entertain the idea of class 50s at ED (the question was posed and the rumour about in the early 8os as the IC 125s displaced 50s from their top spots in the course of less than 6 years. This rumour may have come with the fact that ED was ridding itself of 6LDA sulzers with then three or four types of EE SVT/CSVT locos being manageable) He said a new class in ScR was a bad idea in terms of crew training, spares and repairs.

The 31 Brush type two had been "failed" for services on the west highland line in its rather puny Mirlees day, but the SVT 1470 hp unit may have fitted rather well into ED as a depot. However, it would mean all the above Chris Green mentions,  despite their eminence in the reliability stakes.

Also there was another point of view- 37/4s would have to work both bigger passenger trains, and as an allocation to ED would work freights. The CP7 bogie offered the ideal solution for all round services out of ED where there is little opportunity for 37s to work at 90mph anyway on the allocated RA5 services, while often pairs had to be used to ensure starting and progress on WHL freights which were subsequently handled by a single 37/4.

A really grand allocation they became then! Being able to work until 2010 on the sleeper if I read correctly and I remember hearing them on the service after 2004 when sleeping at a relative's house near the line- with some disbelief having given up bashing 18 years before!

I gave up bashing for all the right reasons- my era was in those whisps of steam and 37s doing over 90mph when they got let loose on the west coast main line or a replacement Glasgow-Edinburgh service and so on. 37/4s marked modernity and shiny stuff and I nodded and smiled and retired from bashing as they began plying their trade of fast acceleration and better wheel slip control on the routes. Later when I saw they had displaced duffs on Highland Line services a little part of me wanted to get a freedom-of-Scotland and clear some numbers and lines but really that was just a tiny part of me by then. A lot of bashers went on to misspend youths and budding romances by carrying on with the several incarnations of liveries and routes the 37s then went on to work, and I am glad for them and glad that I did not follow them!

Class 37 Self Steering "Bendy Bogies" (CP5)

  The desire for more power to move passengers faster and lift heavier freights on the west highland line, and lines north of Inverness, lead to the obvious candidate being the RA5 EE type 3 aka the class 37, 1750hp CoCo loco. In a techincal paper recently made available I find a fascinating insight into what was a class novelty soon brushed under the carpet by 1986, namely the "bendy bogie" experiment.

As a design, the CoCo bogie has many advantages, but one challenge is getting them to go round curves and we have a lot of those in the Highlands of Scotland!

The fact is of course that Class 37s had a much longer history with the ScR than most bashers and cranks knew, although that being largely a non boilered allocation to Eastfield and Grangemouth and thus in fact, their use limited due to demands for steam heating even in May and late August on these routes.

It seems that the WHL was not a route of choice for 1960s controllers allocating out EE type 3 motive power, and I propose they were probably either a) reserved for medium weight coal and petrochemical freights elsewhere ;  or b) banned from the route due to Co Co configuration.

Prior to tests of boilered EE type 3 locomotives at some point around 1977-78, I never saw myself or heard any "tractors" living within earshot of the route, nor did I see then or now any photos of 37s on even freights up there despite a decade of allocation to relevant depots. Someone will no doubt correct me and please, be my guest!

The Background History, Geography, Engineering and Economics!

By the late 70s, the mainstay of WHL traction, the class 27s, were becoming unreliable and there was a desire to have faster timetables on the west-highland line in order to compete with road transport. To put it in perspective, 27s ran a timetable almost 50 minutes longer from ft william and suprisingly 40 minutes from Oban. In a later twist of irony, these timings are similar  to sprinters which required a fudging of class 37 timetables in order to look competitive.

Road improvements at various points on the Mallaig to Glasgow "A82", the  road-to-the-road-to-the-Isles as they call it, were either in planning in the late 70s or actually completed. In order to remain relevant on passenger timings and also to have a synergy with the aluminum and paper industries at fortwilliam and oil/petrol to Oban, then more horse power would be needed and the 37 of course being RA5 with the pulling power (max' tractive effort) as high as many type 4 and even the type 5 deltic, would seem to be ideal (55,000lbs force at 18mph for the EE type 3)

The west highland line however is less than ideal for any locomotive or indeed multiple unit due to its torturous nature in gradients, curves and slippy rails. In steam days the line eventually demanded the somewhat over-spec'ed Black 5 be utilised, but this measure of power and superior tractive effort prove successful in steam as it did in diesel with the essentially more power than needed class 37. Many steam fans in their 40s and 50s would tell us that the black 5s would out perform the little tin-cans in classes 24,25,26,27 and 29 which replaced them from the route.

At one point there was chat and a reference in some rag about the 37s speeding up timetable and improving cornering. Perhaps that was either wishful thinking or outright propaganda then. BR was already planning for some way of working around this and although open to modification, they did not want to invest in new bogies (although at a cost we heard for a new wheel and axle with driving gears- set of over a hundred grand and this being not infrequent for Eastfield cl 37s it may have been wiser!) Perhaps someone could offer a comment on the BoBo bogies of the various type 2 designs and how the axle to axle span differs or other benefits of the double bogie with fewer axles, but that is immaterial: we were going to get more "horse" and not going to get RA6 Bo Bo class 33s up the WHL!!

They Knew All Along About CoCo Issues to be Found midst Lochs and Mountains Then? 

British rail technical and the class 37 fleet management in operational engineering must have known about the potential problems of running at maximum line speeds with a Co Co loco from experience with such routes in Wales, and it is reported that some modifciations, or tweaks, to the existing bogies on ED allocated "syphons" were made to allow probably for a more compliant ride at cost of some high speed stability ( with better track bed and in particular modern points, this was probably not such  an issue as it had been in late 40s BR!)

Eastfiled locos turned out with a white stripe at the tumble home bend on the locos body sides to denote this apparently, while I do not recall 37 175 having this actually, and we believed the time that 081 had it for some ceremonial/royal/tour working with an ETHEL. I do seem to remember that the white stripe denoted a speed limit on the specific locos though.



UK DE loco Bogie Design from 1947-1990 : A Fundemental Fudge ?

British locomotives like any other have vertical suspension, with the springs and dampers an obvious part of the construction. Hidden from view, the traction motors are "nose suspended" to the internal main-frame of the bogie with their own suspension such that they can ride with the axle while being cushioned from verticle shocks and horizontal movements.

Now here is the rub, you must also spring and dampen horizontal movements, because you do not want the massive forces created by the usual uneven ride of a loco as it rolls, pitches and yaws ; three aircraft and nautical terms for "shoogeling" as in Glaswegian.

Essentially this then has more to do with building engineering for earthqaukes, in reverse, where the mass which is oscillating is above the earth! There is a requirement to reduce impact forces on corners and dampen any horizontal movement transverse to the direction of travel.

So the bogies allows for this in the "commonwealth" type by having a main frame higher up in the bogie with the main circular bearing the bogie rotates under the loco on, while the axles and traction motors are then suspended on other structures which allow for some independent movement. Conversely, the characteristic 'cantilever" beam of this type of bogie  then holds all three axles vertically compliant and transmits these conjoined elements and forces to the suspension springs.

So in this way the wheel set can move to follow the rail even if the loco above is pitching, rolling or yawing, and dampen the forces. Further to this then the axles and traction motors can move to a given degree of horizontal independence with the vertical forces being resolved by the cantilever beam.

As young spotters then, we thought that the cylinder and rod arrangements on this type of bogie were brake pistons, but in fact these are an ingenious part of the system to control the extent of horizontal, independent movement while actually being laterally mounted to fit in the space available to the BR gauge.

Compromise Makes for A Good All Round Bogie System in the UK:

The independent axles main advantage is of course actually in tackling curves of a radius shorter than cant of the line and wheel bevel angle would not require this (as in fact is part of the practice of very high speed trains now, where unwanted horizontal movements under application of tractive effort or braking resistance may set up oscillations, greatly amplified by the high speed: hence HS1 and HS2, bullet train in Japan and the whole TGV thing running on very shallow curves with enormous radii) The axles of a locomotive or rolling stock for that matter must to some extent follow the radius of the curves which are sharper than allowed for in the tolerances of the higher-speed-track bed solution.

Essentially despite the whole bogie rotating around a sensible designed pivot point on the loco, the wheel set when presented with a prominent curve shall we say, are on one side forming a cord on the arc of the rail and on the inside trying to form a tangent. This has to be further corrected for in order to reduce wear to both the track and the bogies, in particular the wheel flanges and tyres but also other components which we will discuss here.


The system design then for a limited amount of independent axle transverse movement has three purposes which relate in their entirety to safe progress:

1) reduce forces on the track: ie the bogie tries to educate the radius to the "chord" between contact point and indeed between bogies.

2) reduce wear on the locos flanges and other components

3) make the ride smoother and both spring load the sideways forces and dampen them  to further this end.


Articulated Bogie Designs (eg Class 66)

Most north American locomotives do not use this approach of significant, radius-following, independent axle movement, but rather allow for a limited articulation in the  whole bogie frame design: often on CoCo design, the innerst axle pivots or rather has a limited rotation on its own frame rather than the axles itself "floating". There are probably some unwanted effects of this under traction and breaking, or over poor points etc, and with transmission/suspension of vertical forces  but now this is of course very wide spread in the UK being a feature of the class 66. For lower speed routes where it is desirable to reduce wear on the flanges and the tyres  on the wheels and the axles, gears, armatures and bearings, it would seem that this would be a better solution.

However the class 37 and most of its contemporaries were based on proven technology from the 1950s and before even, from successful and reliable designs  in the emerging diesel electric traction field. Ironically though, many steam locomotives feature a trailing wheel under the cab behind the main driving wheel which is articulated !!. The issue did not come up until the 37s were sent to Terra Scotia en masse! By then the articulated frame approach had been proven too at various speeds and track beds were far safer for modern locos to ride at higher speeds over.

Typical British Approach: Boffins with Cotton Reels.... Make Do And Mend with Ingenuity 

Confronted with a limited budget for a limited end  benefit in terms of return-on-investment then the engineers were faced with compromise and make-do-and-mend.  Typical for the political atmospehere at the time, the usual public funding issue of getting a budget to repair unsuitable materials every year, but never a larger budget in one year to eliminate or engineer out those issues, no doubt played a part. 37 bogies' would then need to "shoogle" more, yet not cost the earth to do so.

I can imagine the early tweaks were then to allow for softer sideways "preload" so that the axles could react quicker and perhaps small adjustments in the total horizontal movement possible. However, a bit like a plank of wood getting nailed down really hard at one end and the other springing up, eventually you are going to reach a limit of movement in part of the system and that prove to be critical in the "nose suspended" traction motor suspension. This has both an unfortunate simple leverage effect which could amplify small adjustments in axle transversing and also of course this is the absolute key to motive power thus being expensive to get wrong.

To summarise this fascinating article as a layman; and I hope I do justice for the inginuity of the engineers back then:

1. The nose suspension box for the traction motors was critical and modified to include an "X" shaped rubber suspension element to allow for more movement from more directions
2. The axles were engineered or allowed to run further in the lateral direction and to do this quicker
3. New side ways springs and dampers were employed to then work with this longer and faster lateral travel

Success in Engineering and Failure in Economics

The trials with the bogie were evaluated as being very positive, as detailed to a very high technical degree in the paper . The results showed that the new design conformed to tolerances for these type of movements on tracks, thus being safe and the prediction was that there would be significantly less wear on the wheel sets.

However we were in a position by then of 1985 and "sprinterisation" was planned for and the lower geared 37/4s and eventually /5s would be used on heavy frieghts at lower speeds. It seems most likely to me that there was no capital budget for this adaptation to a set of 12 locomotives or so, which seems very short sighted and a result of the whole annual budget bull shit the Uk was in at the time in all departments: on the one hand not being able to spend more on year to save costs in the subsequent years, while on the other using up as much of the budget you had for operations in order that you didnt get it cut back from the actual spend. From water works to the admiralty, this was the Tory fueled "double think" of the 80s and early 90s.

As I heard from railway staff at the time, a new wheel set for a standard 37 was over 100 grand, and maybe that was higher for the new CP7 lower geared bogie. So spending one year to save for the whole life cycle of a sub class would seem sensible. On the other hand, the actual worse cause of wear was wheel spin and some other forms of wheel-spin-prevention and arrest could have been a wiser investment in terms of cost-benefit-saving.

No matter what, 37s are still today in fact working to Mallaig after having had the longest relationship with the line of any diesel loco, spanning 3 decades.