Why did First Generation DMU's have gears?

[MadMac]

Ultimately yes, because it was done as a test in about 1956.

The BR Davey-Paxman experimental set proved the theory and was capable of some 90mph.

Some info on the Davey-Paxman set HERE.

 

[Richard Scott]

At the time hauled rolling stock generally was vacuum braked, and electric MU stock was air braked. DMUs had both air and vacuum supplies, the air drove things like the throttle motors and the vacuum did the brakes. Reason for this choice was so they could take vacuum braked stock as trailers. Not done a lot but it was in early times, then tailed off. Taking a van on some routes happened, and the WR would add a hauled coach on the back if necessary for passenger loads. These were then of course a nuisance at the terminus, where the whole dmu formation would need to run round what they had hauled, unless there was a shunting locomotive.

Southern was almost exclusively air braked by then and conventional DMUs were vacuum so not really in keeping with what Southern already had, that was what I meant.
I do know how a DMU works, have driven many of them!

 

[Helvellyn]

Some info on the Davey-Paxman set HERE.

Interesting to note that although experimental the unit was more powerful than any BR second generation DMU, where the Class 158s/165s/166s were fitted with 350hp engines (plus ten 158s and the 158s with 400hp ones).

On paper many first generation DMUs were more powerful than the second generation ones, with 300hp per car for power twins (360hp for Class 110/111 if operating as twins). As built Pacers were 200hp per car; Sprinters 285hp per car.

 

[Gonzoiku]

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.

The Napier Deltic power unit was initially used in smaller naval vessels, only later adopted for railway locomotives. But I suspect few Class 55 locomotives were ever found at Laura

GZ

 

[Richard Scott]

The Napier Deltic power unit was initially used in smaller naval vessels, only later adopted for railway locomotives. But I suspect few Class 55 locomotives were ever found at Laura

GZ

High speed engines are generally considered those that run at 1500rpm or higher, which the Maybachs and MANs in Hydraulics did. I doubt all naval vessels were powered by Deltic engines either but by a variety of types?

 

[Gonzoiku]

High speed engines are generally considered those that run at 1500rpm or higher, which the Maybachs and MANs in Hydraulics did. I doubt all naval vessels were powered by Deltic engines either but by a variety of types?

Ton and Hunt class MCM vessels, I believe. Possibly also high-speed launches, but those would be RAF not RN!

GZ

 

[ac6000cw]

I doubt all naval vessels were powered by Deltic engines either but by a variety of types?

The Paxman Valenta (as fitted originally in the HST power cars) was AFAIK initially developed for Naval use. I think some other Paxman diesel engines also had Naval heritage.

I think many larger rail-traction diesel engine designs were either originally developed with marine use in mind (e.g. Sulzer?) or have been extensively used in marine applications (e.g. EMD has long had a substantial marine market, in the US at least).

 

[Richard Scott]

The Paxman Valenta (as fitted originally in the HST power cars) was AFAIK initially developed for Naval use. I think some other Paxman diesel engines also had Naval heritage.

I think many larger rail-traction diesel engine designs were either originally developed with marine use in mind (e.g. Sulzer?) or have been extensively used in marine applications (e.g. EMD has long had a substantial marine market, in the US at least).

Valenta was definitely a marine engine. Was speaking to the person who designed the fuel system to convert it to rail usage a while back!
A lot of rail engines were originally used in other applications such as marine or standby generation. When I worked for a water company many years ago a lot of standby generators had engines with a clear English Electric heritage!!
Think a lot of engines used in rail started life elsewhere hence use of bus engines in DMUs? As an aside there were/are some small shunters in Denmark that use a Leyland 0680 engine so bus engines even found their way into the shunter market!

 

[ac6000cw]

On paper many first generation DMUs were more powerful than the second generation ones, with 300hp per car for power twins (360hp for Class 110/111 if operating as twins). As built Pacers were 200hp per car; Sprinters 285hp per car.

I've mused on that too - one issue with the 1st gen DMUs with mechanical transmissions was the slowness of the gear changes - it involved shutting off power, waiting for the engine revs to drop down, then changing gear, waiting a few seconds to ensure all of the multiple gearboxes had time to change, then applying power again. Particularly on steep rising gradients, the train could lose a reasonable amount of speed during a gear change. Whereas the transmissions on the 2nd and later gen DMUs provide seamless torque - and maybe the 2nd gen Cummins + Voith combo is well matched in terms of power and torque characteristics?

 

[Richard Scott]

I've mused on that too - one issue with the 1st gen DMUs with mechanical transmissions was the slowness of the gear changes - it involved shutting off power, waiting for the engine revs to drop down, then changing gear, waiting a few seconds to ensure all of the multiple gearboxes had time to change, then applying power again. Particularly on steep rising gradients, the train could lose a reasonable amount of speed during a gear change. Whereas the transmissions on the 2nd and later gen DMUs provide seamless torque (and maybe the 2nd gen Cummins + Voith combo is well matched in terms of power and torque characteristics?

The gear changes also reduced torque considerably, which didn't happen to the same extent on 2nd generation units even when they went from torque converter to direct drive. Despite inefficiency of the second generation unit's transmissions, when in torque converter mode, they gave more seamless torque characteristics. They also made use of full engine power from almost a standing start hence superior acceleration.

 

[ac6000cw]

The gear changes also reduced torque considerably, which didn't happen to the same extent on 2nd generation units even when they went from torque converter to direct drive. Despite inefficiency of the second generation unit's transmissions, when in torque converter mode, they gave more seamless torque characteristics. They also made use of full engine power from almost a standing start hence superior acceleration.

I agree. I also find the acceleration performance of the 3rd gen DMUs with 6-speed ZF automatic transmissions very impressive (helped by 500hp diesel engines of course).

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Think a lot of engines used in rail started life elsewhere hence use of bus engines in DMUs?

They did - I think buses and coaches are traditionally the main market for horizontal engines. Roger Ford mentioned in MR once that the MTU-branded engines in the 168s and 170s were originally designed as Mercedes bus engines (as of course were the Leyland/Albion/AEC engines in the 1st gen DMUs).

As an aside there were/are some small shunters in Denmark that use a Leyland 0680 engine so bus engines even found their way into the shunter market!

Several classes of small BR shunters had 6 and 8 cylinder Gardner engines, which was a popular engine supplier with bus (and truck) operators for years.

 

[norbitonflyer]

A lot of rail engines were originally used in other applications such as marine or standby generation. When I worked for a water company many years ago a lot of standby generators had engines with a clear English Electric heritage!!

The two used in tye LMS Ivatt twins were from a batch built for such use. One of them survived long enough to become the nucleus of the Ivatt replica now being built.

(Secondhand standby generators can be very good prospects for further use, as they will have been maintained to a high standard but hardly used).

== Doublepost prevention - post automatically merged: 29 Oct 2025 ==

Several classes of small BR shunters had 6 and 8 cylinder Gardner engines, which was a popular engine supplier with bus (and truck) operators for years.

As far as i can tell, the only shunters with mechanical transmisions to not have Gardner engines were two Ruston & Hornsby shunters D2957 and D2958, which had Ruston's own engines

All of those built by Barclay, Drewry, Hudswell Cklarke and Hunslet , as well as the BR-derived version of the Drewert design, had the gardner enegine

Class 01 and pre-TOPS class D1/1 (Hunslet D2950 class) had the 6 cylinder engine (both 0-4-0s)

Classes 03-06, and D2/5 (Barclay, D2400), D2/7 (Hudswell Clarke, D2500), and D2/12 (Hudswell Clarke, D2510) all had the eight cylinder engine - all 0-6-0s except class 06

 

[The exile]

Several classes of small BR shunters had 6 and 8 cylinder Gardner engines, which was a popular engine supplier with bus (and truck) operators for years.

Sure I’ve read somewhere that following the premature withdrawal of shutters, the reconditioned engines found a second home in fishing boats.

 

[D6130]

Sure I’ve read somewhere that following the premature withdrawal of shutters, the reconditioned engines found a second home in fishing boats.

I think that referred to the Mirrlees engines which were replaced by English Electric ones in the class 30/31s....but I can't quote a source offhand.

 

[matchmaker]

I agree. I also find the acceleration performance of the 3rd gen DMUs with 6-speed ZF automatic transmissions very impressive (helped by 500hp diesel engines of course).

== Doublepost prevention - post automatically merged: 29 Oct 2025 ==


They did - I think buses and coaches are traditionally the main market for horizontal engines. Roger Ford mentioned in MR once that the MTU-branded engines in the 168s and 170s were originally designed as Mercedes bus engines (as of course were the Leyland/Albion/AEC engines in the 1st gen DMUs).


Several classes of small BR shunters had 6 and 8 cylinder Gardner engines, which was a popular engine supplier with bus (and truck) operators for years.

Very popular as marine engines as well. Many RNLI lifeboats of the 1950s and 1960s had Gardner 5LW, 6LW or 8LW engines.

 

[Gloster]

Sure I’ve read somewhere that following the premature withdrawal of shutters, the reconditioned engines found a second home in fishing boats.

I believe that R.E.Trem Ltd specialised in this and that many of the shunters they purchased had the motors removed before the loco was scrapped at one of the main scrapyards. The motors were then refurbished, presumably at Trem’s Doncaster (Finningley?) yard, and them sold on, particularly for use in trawlers.

 

[Richard Scott]

I think that referred to the Mirrlees engines which were replaced by English Electric ones in the class 30/31s....but I can't quote a source offhand.

They did too but the Gardner engines in shunters definitely were in demand for fishing vessels etc