Class 755 Bi-Mode

[andy33gmail]

To the end of using Split ticketing and advance tyres, today I went from Liverpool Street -> Cambridge on a 720, then Cambridge -> Ely on a 755, then Ely -> Littleport on a 319

First time I'd been on a diesel for a while ... but it made me wonder ... why does the 755 run on dinosaur juice from Cambridge to Ely when there are perfectly good overhead lines?

I appreciate that at somewhere they need to drop the pantograph and start the engine. Is there a reason for doing this in Cambridge rather than Ely other than taking advantage of the longer dwell time in the timetable?

 

[bspahh]

To the end of using Split ticketing and advance tyres, today I went from Liverpool Street -> Cambridge on a 720, then Cambridge -> Ely on a 755, then Ely -> Littleport on a 319

First time I'd been on a diesel for a while ... but it made me wonder ... why does the 755 run on dinosaur juice from Cambridge to Ely when there are perfectly good overhead lines?

I appreciate that at somewhere they need to drop the pantograph and start the engine. Is there a reason for doing this in Cambridge rather than Ely other than taking advantage of the longer dwell time in the timetable?

The changeover from electric to diesel normally happens at Ely.

These are from a thread from 2021 where @dk1 wrote

We are not permitted to changeover power on the move.

and, one what happens if you don't switch to diesel power in time:

I think many of us have found out where it ends at Ely North Jcn & Between Crown Point & Whitlingham lol.

The Pan Protection Zone is to do with the 755s themselves. It’s in an area that GPS detects the pan is raised but will shortly run out of wire. It drops the pantograph & applies the emergency brake so as no damage is done. Driver then starts Diesel engines & continues on his/her way with their tail between their legs.

 

[andy33gmail]

Interesting. Any idea why they sometimes don’t?

I was near the middle of the train - near the narrow corridor bit - and I’m absolutely certain the engine was running & being used like a normal DMU (aka revving like a teenager in a stolen diesel car whilst accelerating like an undertaker)

 

[RailwayRookie]

To the end of using Split ticketing and advance tyres, today I went from Liverpool Street -> Cambridge on a 720, then Cambridge -> Ely on a 755, then Ely -> Littleport on a 319

Pedants corner but that would have been a 379 or potentially 387. (Or depending on time a 700 but thats a 1 in 25 chance)

 

[dk1]

Interesting. Any idea why they sometimes don’t?

I was near the middle of the train - near the narrow corridor bit - and I’m absolutely certain the engine was running & being used like a normal DMU (aka revving like a teenager in a stolen diesel car whilst accelerating like an undertaker)

The engines work very differently to older class 15X units. They do not rev on initial acceleration. Under normal circumstances they would not be running until arrival at Ely in the down direction although some drivers do pre-start them on approach particularly in cold weather although it’s not mandatory.

 

[andy33gmail]

Pedants corner but that would have been a 379 or potentially 387. (Or depending on time a 700 but thats a 1 in 25 chance)

379 sorry. Specifically the one where the lead coach had black graffiti all over it

The engines work very differently to older class 15X units. They do not rev on initial acceleration. Under normal circumstances they would not be running until arrival at Ely in the down direction although some drivers do pre-start them on approach particularly in cold weather although it’s not mandatory.

It was certainly cold. So that fits

I wonder now whether they started up the engines right around the time they left Cambridge; so I conflated a start-up sound with an acceleration sound?

 

[Railperf]

To the end of using Split ticketing and advance tyres, today I went from Liverpool Street -> Cambridge on a 720, then Cambridge -> Ely on a 755, then Ely -> Littleport on a 319

First time I'd been on a diesel for a while ... but it made me wonder ... why does the 755 run on dinosaur juice from Cambridge to Ely when there are perfectly good overhead lines?

I appreciate that at somewhere they need to drop the pantograph and start the engine. Is there a reason for doing this in Cambridge rather than Ely other than taking advantage of the longer dwell time in the timetable?

It is possible the unit may have been on a diesel only restriction due to an issue with the pantograph or some other electrical issue.

 

[dk1]

379 sorry. Specifically the one where the lead coach had black graffiti all over it

It was certainly cold. So that fits

I wonder now whether they started up the engines right around the time they left Cambridge; so I conflated a start-up sound with an acceleration sound?

If the pantograph was raised the engines would not be powering the train so would just be idling. Maybe you heard the intial start up where they fire up separately but it wouldn’t be as far back as Cambridge under normal circumstances.

 

[Railperf]

If the pantograph was raised the engines would not be powering the train so would just be idling. Maybe you heard the intial start up where they fire up separately but it wouldn’t be as far back as Cambridge under normal circumstances.

What's the earliest point after leaving cambridge you might start the engines on a very cold day? Do the engines have a pre-heat system that initiates before fire up?

 

[dk1]

What's the earliest point after leaving cambridge you might start the engines on a very cold day? Do the engines have a pre-heat system that initiates before fire up?

Approaching the new Ely bypass bridge is a favourite for many. No, no pre-heat setting. Just start the diesel engines so they warm up slightly before taking load.

 

[andy33gmail]

The engines work very differently to older class 15X units. They do not rev on initial acceleration. Under normal circumstances they would not be running until arrival at Ely in the down direction although some drivers do pre-start them on approach particularly in cold weather although it’s not mandatory.

This roughly aligns with what I heard:

I get that it’s more refined than quieter than a 158 (

)

But even so, I’m missing the fundamental difference … diesel engine revs, acceleration follows

 

[Railperf]

Approaching the new Ely bypass bridge is a favourite for many. No, no pre-heat setting. Just start the diesel engines so they warm up slightly before taking load.

Has there been any noticeable adjustments to the performance of the units - either due to age or fine tuning to aid reliability? Are most of the units running all-engines or do you still get quite a few units with an engine out?

== Doublepost prevention - post automatically merged: 27 Nov 2025 ==

This roughly aligns with what I heard:

I get that it’s more refined than quieter than a 158 (

)

But even so, I’m missing the fundamental difference … diesel engine revs, acceleration follows

There is a rise in engine speed on the 755's as they start moving. Nothing touches a 755/4 for diesel acceleration. It may not make the same sound, but boy they accelerate like an electric unit. The 755/3's are not quite as quick but match a Class 80x on diesel! In fact there are so many 80x running with engines out of action that they are indeed slower than a 755/3.

 

[dk1]

Has there been any noticeable adjustments to the performance of the units - either due to age or fine tuning to aid reliability? Are most of the units running all-engines or do you still get quite a few units with an engine out?

== Doublepost prevention - post automatically merged: 27 Nov 2025 ==


There is a rise in engine speed on the 755's as they start moving. Nothing touches a 755/4 for diesel acceleration. It may not make the same sound, but boy they accelerate like an electric unit. The 755/3's are not quite as quick but match a Class 80x on diesel! In fact there are so many 80x running with engines out of action that they are indeed slower than a 755/3.

As far as I’m aware they’ve been far more reliable since the Deutz engine changes. Occasional pantographs isolated but nothing unusual. Stadler appear to be doing an excellent job and backed up by yet another golden spanner for the 755/4 fleet. I left in July so haven’t heard anything different from the ex-colleagues I meet up with.

== Doublepost prevention - post automatically merged: 27 Nov 2025 ==

This roughly aligns with what I heard:

I get that it’s more refined than quieter than a 158 (

)

But even so, I’m missing the fundamental difference … diesel engine revs, acceleration follows

Most 15X units will give the revs if going straight or at low speed into notches 6/7. The 755s rarely have the fans screaming these days particularly in winter. It was prolific around 2020/21 until further software updates were done.

 

[317 forever]

To the end of using Split ticketing and advance tyres, today I went from Liverpool Street -> Cambridge on a 720, then Cambridge -> Ely on a 755, then Ely -> Littleport on a 319

First time I'd been on a diesel for a while ... but it made me wonder ... why does the 755 run on dinosaur juice from Cambridge to Ely when there are perfectly good overhead lines?

I appreciate that at somewhere they need to drop the pantograph and start the engine. Is there a reason for doing this in Cambridge rather than Ely other than taking advantage of the longer dwell time in the timetable?

Given that you split your ticket, I hope you got a Greater Anglia single from Cambridge to Ely rather than a fully flexible single.

I did yesterday so best of both worlds - a rare (in national terms) 755 and saving £1 in the process

 

[saismee]

We are not permitted to changeover power on the move.

An inaccurate quote now as there are dynamic changeover points (Haughley Jn as an example). I imagine they weren't there at the time.

 

[dk1]

An inaccurate quote now as there are dynamic changeover points (Haughley Jn as an example). I imagine they weren't there at the time.

Yes of course. That was bloody years ago lol.

 

[andy33gmail]

Given that you split your ticket, I hope you got a Greater Anglia single from Cambridge to Ely rather than a fully flexible single.

I did yesterday so best of both worlds - a rare (in national terms) 755 and saving £1 in the process

Advance single & advance single from ELY to LST, booked about a month in advance

Then a “normal” return from LTP to ELY

Always up for cheaper options if they exist, the cost of commuting is brutal

== Doublepost prevention - post automatically merged: 11 Dec 2025 ==

I ended up taking a similar journey yesterday.

I tried to get off quickly at Ely and listen for a start up sound … but it was a little hard to tell for the sound of a clapped out class 170 Cross Country

Was briefly concerned to see it making off with the panto still up … turns out they can drop them later now: https://www.greateranglia.co.uk/abo...eet-regional-trains-set-save-thousands-litres