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Driving a DMU

Some Do's Don'ts and Remembers...

(Compiled by Stan Acaster (Dean Forest DMU Group))

DO... only have ONE set of keys, ONE reversing level and ONE brake handle in use on any ONE train.

DO... ensure that a final drive isolating rod is available.

DO... ensure before attempting to start the engines from the cab, that at least 75 p.s.i. air pressure is available BEFORE placing the reversing lever in the desk.

If less than 75 p.s.i. is registered or the engines are cold, put the reversing lever in your pocket and start the engines locally. After starting the engines locally and sufficient air pressure is obtained, DO STOP the engines before inserting the reverser in the desk. After stopping the engines the reverser may be inserted and the engines restarted from the cab in the normal manner.

DO NOT... race the engines when starting them. If they are not warm they may need full throttle to start but they should be eased off to a fast 'tick over' as soon as possible.

DO NOT... keep a start button depressed for more than three seconds or persist in trying to start an engine if the starter motor fails to turn the engine. Doing so will rapidly 'flatten' the battery, burn out the starter motor and damage internal cabling.

DO... wait for at least 10 seconds to allow an engine to come to rest if it fails to start, before pressing the start button again. Pressing the start button before an engine has come to rest causes severe damage to starter pinion and starting ring teeth.

DO... stop an engine by manually operating the shut down solenoid if it fails to stop when either the cab or local stop button is pressed. If the engine is not stopped when the shut down solenoid fails to operate it is not protected against low lubricating oil pressure, low water level or fire.


DO NOT... race engines to increase air pressure if an Air/Axle light is out, doing so will damage the final drive teeth.

Before Moving Away

DO... ensure that the vacuum brake is 'lapped' at approximately 15" of vacuum.

Moving Away

DO... select Gear 1 and release the vacuum brake, pausing 2 seconds after gear 1 has been selected before opening the throttle NOTCH by NOTCH.

DO NOT... allow a train to roll backwards with a gear engaged.

Should it inadvertently do so, stop the train with the brake - NOT by opening the throttle - as this can cause the cardan shaft to become twisted.

If Wheel Spin Occurs

DO... close the throttle and allow wheel spin to stop, then try notch 1 or 2 to start the train.

Gear Changing

DO NOT... try to be a 'quick change artist' this causes damage to the gearbox as well as giving passengers an uncomfortable ride.

REMEMBER... railcar gearboxes are NOT similar to the usual car gearbox on which quick gear changing is not harmful.

Changing Up

When the tachometer shows 'CHANGE UP' close the throttle and:

DO... wait until the engine 'revs' fall to at least below the half way mark in the yellow sector (approx. 4 secs.) before selecting the next higher gear. (When driving from torque converter cars pause 4 seconds before selecting next higher gear).

DO... pause for 2 seconds AFTER selecting the next higher gear BEFORE opening the throttle NOTCH by NOTCH.

REMEMBER... it is just as easy to do it the RIGHT way as the WRONG way. When road conditions permit, a smooth change up from 1st to 2nd gear can be achieved by allowing the engine 'revs' to fall out of the yellow sector before selecting gear 2.

Changing Down

When the tachometer shows CHANGE DOWN, close the throttle and immediately select the next lower gear, but ...

DO... pause for 2 seconds AFTER selecting the lower gear, BEFORE opening the throttle NOTCH by NOTCH.

REMEMBER... It is just as easy to do it the RIGHT way as the WRONG.

DO... stop an engine if it fails to return to idling when the throttle is cleared, otherwise severe damage will be caused to the gears.

On Long Rising Gradients

DO NOT... 'flog' the engines and transmissions by remaining in a gear which keeps the engine 'revs' between 1,100 and 1,200 r.p.m. as this overheats the fluid coupling. It is better to select the next LOWER gear until the gradient is more favourable for the higher gear.


DO NOT... coast in any other gear than the 4th. Coasting in gears 1,2, and 3 overspeeds the gearbox gear trains and causes excessive wear.

DO... wait until the engine 'revs' have dropped to idling before selecting 4th gear when it is necessary to coast at LOW speeds.

DO... select NEUTRAL just before coming to a stand. Standing with ANY gear engaged for more than a few seconds will rapidly overheat the fluid coupling.

REMEMBER... It is just as easy to adopt the correct driving technique as the incorrect.

Bad driving technique causes a rapid deterioration in the mechanical condition of gearboxes and final drives, which, in turn, results in the premature withdrawal of diesel trains from services.

This results in a severe and unnecessary loss in the revenue earning capacity of a fleet of diesel trains, and at times having to bring in steam hauled trains to maintain a service.


DO... make use of the 'LAP' position of the brake valve.

DO NOT... 'see-saw' the brake valve handle between the ON and OFF positions when making a brake application. It is unnecessary and results in the release pipe vacuum being low on coming to a stand and consequent difficulty in releasing the brake when restarting. This gives rise to the annoying and unnecessary practice of 'revving' engines in stations to obtain vacuum.

DO... on coming to a stand, release the brake to about 15" of vacuum, then place the brake valve to the LAP position. This allows the release pipe vacuum to build up sufficiently to give a 'quick release' of the brake when ready to move away.

REMEMBER... the higher the release pipe vacuum the quicker the brake release.

Prep and Basic Technique
General Info
Do's Dont's and Remembers ->
What do I do if...?
Fault Finding
Jumpers Disconnected

Driving a mechanical transmission DMU meant changing gears, those that had hydraulic transmission didn't (unless they were coupled to a mechanical DMU).

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