Why did First Generation DMU's have gears?

[Iskra]

Quick question; Why did First Generation DMU's have manual gears? Particularly when diesel locomotives of the same era didn't?

 

[jadmor]

The simplest answer is that they had a mechanical drive, not a million miles away from a truck or bus set up. I don't have the links but there is a set of Youtube videos filmed for training when the DMUs were introduced that show the transmission in action.

 

[Ashley Hill]

there is a set of Youtube videos filmed for training when the DMUs were introduced that show the transmission in action

It’s a BTF film called Diesel Train Driver. Part Two has the relevant section featuring the epicyclic gearbox. Here’s a link.

 

[hexagon789]

Quick question; Why did First Generation DMU's have manual gears? Particularly when diesel locomotives of the same era didn't?

Most did, but not all.

I suspect some commonality with buses of the time played a major part, but also the diesel railcars already in service before the BR 1st gen units were generally mechanical units - the GWR having an appreciable number that passed to BR and which were mostly pure mechanical transmission. (Some of the earlier railcars had a split mechanical/fluid-flywheel arrangement.)

The transmission arrangement is pretty much the same on the latter batches of GWR railcars as the mechanical 1st gen BR units.

 

[ac6000cw]

Quick question; Why did First Generation DMU's have manual gears? Particularly when diesel locomotives of the same era didn't?

Some diesel shunting locos did have 'manual' gears e.g. the 03's, and the class 127 DMUs had hydraulic/torque converter transmissions (which could operate automatically).

Most BR diesel locos had electric transmission (which doesn't need multiple gear ratios between motor and axle) or hydraulic transmissions using torque converters - these can maintain continuous tractive effort during acceleration, which is important to avoid snatching/jerks/run-ins which risk breaking couplings etc.

 

[43096]

The simplest answer is that they had a mechanical drive, not a million miles away from a truck or bus set up. I don't have the links but there is a set of Youtube videos filmed for training when the DMUs were introduced that show the transmission in action.

The even more simple answer was cost.

 

[Richard Scott]

Some diesel shunting locos did have 'manual' gears e.g. the 03's, and the class 127 DMUs had hydraulic/torque converter transmissions (which could operate automatically).

Most BR diesel locos had electric transmission (which doesn't need multiple gear ratios between motor and axle) or hydraulic transmissions using torque converters - these can maintain continuous tractive effort during acceleration, which is important to avoid snatching/jerks/run-ins which risk breaking couplings etc.

Slight technicality, Hymeks and 42s had Mekydro transmission which did use a 4 speed gearbox albeit an automatic one so only had one torque converter. I know other hydraulic classes had a set up using 3 torque converters. Being a shade pedantic, I know!

 

[whoosh]

Most diesel locomotives were diesel electric, so the diesel engine drove a generator or alternator, and the electricity from this powered electric motors on the axles.

Most diesel multiple units are diesel mechanical and drive the axles through a gearbox. Semi-automatic gearboxes were common on buses from the 1950s up until the 1980s. These were used on first generation DMUs, and with the glass bulkheads these had, you could see the driver changing gear with one of the control handles.
Sprinters and Pacers onwards were fitted with fully automatic gearboxes. You can usually hear them change gear around 40mph and around 70mph. I *think* class 170s have a further gear which is changed into around 90mph.
Apparently, class 197s have a six speed automatic gearbox. This fits into the pattern car manufacturers have had of having more gear ratios to keep the engine in a better emissions power band.

 

[hexagon789]

Sprinters and Pacers onwards were fitted with fully automatic gearboxes. You can usually hear them change gear around 40mph and around 70mph. I *think* class 170s have a further gear which is changed into around 90mph.

All the 2nd gen BR hydraulic units (and the Pacers converted to this arrangement), plus the post-privitisation DMUs with hydraulic transmission have just two "gears". The only exceptions are the 185s and 180s which have three.

75mph Sprinters will "change-up" at approximately 45mph under full power, but at around 30mph in low power notches. 158/159s are about 55mph, 168/170/171 are about 70 and 175s about 60.

185s with the three stages are around 55 and 80mph; 180s are about 70 and 95mph.

Pacers originally had a four-speed mechanical transmission, very similar to that on the 1st gen DMUs.

Apparently, class 197s have a six speed automatic gearbox.

They are a hybrid arrangement - hydro-mechanical with a torque converter for starting/low-speed, then five mechanical gears.

 

[AY1975]

Most did, but not all.

Which classes of first generation DMU didn't have gears?

 

[hexagon789]

Which classes of first generation DMU didn't have gears?

Derby Lightweights with Red Triangle coupling code.

Classes 113, 125 and 127.

Those all had hydraulic transmission of a few different arrangements.

 

[43096]

75mph Sprinters will "change-up" at approximately 45mph under full power, but at around 30mph in low power notches. 158/159s are about 55mph, 168/170/171 are about 70 and 175s about 60.

Which is presumably why the Turbostars feel so sluggish in comparison with a 158 or 175.

 

[Krokodil]

Which classes of first generation DMU didn't have gears?

127s?

 

[ac6000cw]

Slight technicality, Hymeks and 42s had Mekydro transmission which did use a 4 speed gearbox albeit an automatic one so only had one torque converter. I know other hydraulic classes had a set up using 3 torque converters.

Yeah, I know (hence saying 'Most'), but decided not to complicate the comment/explanation too much

 

[Taunton]

Not only did the 1st gen dmus have mechanical transmission, so did the hundreds of small diesel shunters (smaller than Class 08) as well. Known as the "Wilson" gearbox after its inventor, it was also used in many buses of the era. It didn't need a clutch and was able to shift gears by air pressure, but didn't have the ability to "decide when", so the driver still had to switch gears, the same as buses of the time. It was the most effective gear system to take from the road transport industry of the era, along with engines that likewise were from heavy vehicle manufacturers, and could be bought from them 'off the shelf'. AEC was a major supplier for both railcars and buses, and had worked with the GWR in the 1930s on their pioneer diesel railcars. The AEC works were at Southall, by the GWR main line (nowadays inevitably a housing estate), with private sidings, and they had also been suppliers of pioneer GWR buses. I believe it was a system also used in many French railcars and buses, and likely elsewhere.

It's a simple and cheap power train, but doesn't work well at much over 250hp, when something quite different is needed. The same for motor vehicles - the huge dump trucks of the era at quarries etc with big engines used electric transmission, like a locomotive.

It also helped to have two small engines (with none in the trailers), for overall weight balance, and transmitting to both bogies without the need for convoluted and long transmission shafts

 

[Ashley Hill]

Some diesel shunting locos did have 'manual' gears e.g. the 03's,

I understand that the 03s had an epicyclic gearbox to the design of Wilson as mentioned above.
The smaller shunters (certainly those I’ve had experience with) had a huge lever frame for the gears and a clutch. They were a sod to drive. One you’ve got away in first you would lose speed whilst changing into second and so on.

 

[edwin_m]

With the engines being similar or identical to those used on trucks and buses, it's not too surprising that first generation DMUs also borrowed their transmissions from automotive designs.

This was in contrast to locomotives (other than the small shunters mentioned) whose engines and power ratings are much larger than those of road vehicles. Some smaller ships used similar engines (the Deltic engine being developed for naval patrol boats) but these would traditionally have been connected to the propeller via fixed-ratio gearing. Diesel-electric ships did start appearing about the same time as diesel-electric locomotives, but I'm not sure if there was any cross-fertilisation of ideas between them.

 

[Harpo]

The even more simple answer was cost.

Exactly. It was the cheapest way of doing the job in a low-powered drive train.

Other transmissions were an enforced choice for higher power because the practicalities of mechanical transmission were exceeded.

 

[Richard Scott]

With the engines being similar or identical to those used on trucks and buses, it's not too surprising that first generation DMUs also borrowed their transmissions from automotive designs.

This was in contrast to locomotives (other than the small shunters mentioned) whose engines and power ratings are much larger than those of road vehicles. Some smaller ships used similar engines (the Deltic engine being developed for naval patrol boats) but these would traditionally have been connected to the propeller via fixed-ratio gearing. Diesel-electric ships did start appearing about the same time as diesel-electric locomotives, but I'm not sure if there was any cross-fertilisation of ideas between them.

I may be way off the mark here but believe submarines used electric drives and it was this ban on Germany developing these after WW2 that sent them down the road of developing diesel hydraulic locomotives?
Can anyone confirm or otherwise?

 

[norbitonflyer]

Derby Lightweights with Red Triangle coupling code.

Classes 113, 125 and 127.

Those all had hydraulic transmission of a few different arrangements.

Class 125 had their own unique "orange star" coupling code

And Class 113 were built by Cravens, not Derby

== Doublepost prevention - post automatically merged: 26 Oct 2025 ==

Not only did the 1st gen dmus have mechanical transmission, so did the hundreds of small diesel shunters (smaller than Class 08) as well.

Most but not all of them.

Class 02 is diesel-hydraulic, as were the three classes of North British shunter D27xx and D29xx withdrawn before TOPS classes could be allocated to them (classes D2/1, D2/10, and D3/1) )
Class 07 is diesel-electric, as was the one-off D2999

 

[Taunton]

I may be way off the mark here but believe submarines used electric drives and it was this ban on Germany developing these after WW2 that sent them down the road of developing diesel hydraulic locomotives?
Can anyone confirm or otherwise?

Submarines need to have electric drive because when under water and unable to use their diesel, they use batteries. The diesel both powers them when on the surface and also recharges the batteries.

The navy did go down the route of high speed diesels for their vessels, to save significant weight for the power required. A substantial proportion of the high speed diesel maintenance experts at Plymouth Laira (hydraulic locos, and right up to the HST) are ex-Royal Navy from the engine shops across the city.

 

[Rescars]

I understand that the 03s had an epicyclic gearbox to the design of Wilson as mentioned above.
The smaller shunters (certainly those I’ve had experience with) had a huge lever frame for the gears and a clutch. They were a sod to drive. One you’ve got away in first you would lose speed whilst changing into second and so on.

Was the Wilson gearbox referred to here related to the pre-selector gearboxes used by Daimler, Armstrong-Siddeley and other upmarket car marques pre-war? I recall being given a lift in an Armstrong shortly after I learnt to drive and being intrigued by the unusual driving technique. The driver guessed which gear would be needed next and then moved the lever accordingly, quite a while before pressing the pedal to activate the change of gear. Seems that the driving technique was a bit different on a shunter.

 

[matchmaker]

Was the Wilson gearbox referred to here related to the pre-selector gearboxes used by Daimler, Armstrong-Siddeley and other upmarket car marques pre-war? I recall being given a lift in an Armstrong shortly after I learnt to drive and being intrigued by the unusual driving technique. The driver guessed which gear would be needed next and then moved the lever accordingly, quite a while before pressing the pedal to activate the change of gear. Seems that the driving technique was a bit different on a shunter.

I don't think any diesel locos or units had a pre-selector gearbox. I think all DMUs with mechanical transmission had a drivetrain manufactured by Self Changing Gears Ltd which was a Leyland/AEC company. It was related to the Pneumo-Cyclic gearbox used in Leyland buses of the same era.

 

[hexagon789]

And Class 113 were built by Cravens, not Derby

I know, the "Derby" bit referred only to the lightweights with Red Triangle coupling code that never received TOPS numbers. I thought that description would mean more to most people than the number series would.

 

[MarlowDonkey]

Southern Region DMUs (Thumpers) were diesel electric for compatability with the EMU fleet. They had the diesel engine in the carriage body itself rather than underneath.

 

[RT4038]

I don't think any diesel locos or units had a pre-selector gearbox. I think all DMUs with mechanical transmission had a drivetrain manufactured by Self Changing Gears Ltd which was a Leyland/AEC company. It was related to the Pneumo-Cyclic gearbox used in Leyland buses of the same era.

Which used 'Wilson' patents. Wilson developed the gearbox/transmission originally for tanks in WW1. The technicality behind 'pre-select' compared to the semi automatic by Self Changing gears Ltd is essentially the same - on Pre-select the driver selects the gear and then pushes the operating pedal which mechanically or air assistedly changes the gear, whereas on a semi-automatic the driver selects the gear and simultaneously the gear changes, directly by air assistance or an electric impulse to an electro-pneumatic valve and then air assistance. The gearbox/fluid flywheel are the same/very similar in either application. (as I understand it).

 

[Gloster]

I may be way off the mark here but believe submarines used electric drives and it was this ban on Germany developing these after WW2 that sent them down the road of developing diesel hydraulic locomotives?
Can anyone confirm or otherwise?

I have definitely read in Danish books that such a condition was supposed to have been inserted in the post-war agreements at the insistence of either General Motors or General Electric. I don’t think it was specifically to prevent the development of submarines, just flexing of commercial muscle to hamper competitors.

 

[Krokodil]

I have definitely read in Danish books that such a condition was supposed to have been inserted in the post-war agreements at the insistence of either General Motors or General Electric. I don’t think it was specifically to prevent the development of submarines, just flexing of commercial muscle to hamper competitors.

Anti-competitive practice by General Motors? Shocker.

 

[coppercapped]

I may be way off the mark here but believe submarines used electric drives and it was this ban on Germany developing these after WW2 that sent them down the road of developing diesel hydraulic locomotives?
Can anyone confirm or otherwise?

I find this suggestion that German railways developed diesel hydraulics because they were not allowed to develop submarines somewhat questionable as I cannot imagine which bodies would have been responsible. The Allied Powers controlled the country until the Bundesrepublik was created in 1949 and would not have been interested in building submarines. The first post war U-boat was built in 1960 with design studies starting in the mid-1950s. It took time for the German people to accept the idea of re-armament and even getting the Army set up in 1955 created huge political unrest, building submarines any earlier would not have been politically difficult if not impossible.

This was also the period of Marshall Aid which ran for four years, from 1948 to the end of 1951. It dispensed a total of $12,500 billion to 16 participating members. To manage the funds, it required the establishment of the Organisation for Economic Co-operation and Development (OECD), which insisted that recipients increase production, expand trade, and make 'counterpart contributions' of their own. Although one quarter of Marshall Aid was earmarked for Britain and one-fifth for France, it was available to allies, neutrals, and ex-enemies alike. It seems to me to be very unlikely that that any agreement to restrict trade would have been acceptable during this period.

After Stalin dropped the Iron Curtain across Europe, and right through Germany, the German railways had to be re-orientated to run North-South rather than East-West as the routes to Berlin through East Germany had effectively lost their commercial raison d’etre. At the same time the decision had been made to electrify the new North-South connections as many main lines were already electrified. Diesel traction was limited to secondary routes.

German industry restarted electric locomotive construction soon after the war. It had all the technology available to build diesel-electric locomotives if it had wanted to but the railways had a history of using diesel hydraulic locomotives pre-war which meant that industry and staff were already used to the technology. The company Voith in Heidenheim manufactured, among other things (and still does), paper making machinery, turbines for use in hydro-electric power stations and hydraulic transmissions for various applications including rail. For the power levels required for secondary route use all the components already existed, the more powerful electric Einheitsloks were built for the electrified routes.

It seems to me that the suggestion is far-fetched.

 

[Bevan Price]

Meanwhile, I think that experience with 10100, the Fell diesel locomotive had shown that material technology at that time was incapable of producing satisfactory gearboxes compatible with 2000 hp diesel locomotives....