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Driving a DMU

What do I do if...?

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

Engine will not Motor?

Check battery isolation switch, control isolating switch, engine isolation switch. If these are all right it could be a defective starter motor, starter button, broken connections, flat battery, blown fuse, fire bottle had been exploded and 2-pole switch reset, or burred starter ring. If burred starter ring, turn fluid coupling round to engage good teeth.

Engine Motors but will not fire?

Low fuel or empty fuel tank; Fuel cock shut off; Air lock; Engine shut down solenoid stuck up; Blockage in fuel delivery pipe; Fuel pump defective; Lift pump defective; Air intake blocked. Low water level on modified types.

Engine Motors but ceases to fire when button is released?

Low lubricating oil. Low water level.

Engines will not start from Cab?

Direction not selected. Test button depressed.

In what case would Engine and Final Drive be Isolated?

Low water, low fuel oil, low lubricating oil, air lock, shut-down solenoid stuck up, fuel oil or water in engine sump, knocking in engine, fuel pump coupling broken or loose, throttle motor stuck open, fuel delivery pipe broken, fluid flywheel hot, engine been on fire, propeller shaft broken, gearbox effective, final drive defective air failure, electrical failure, or, IF IN DOUBT ISOLATE.

What would cause Tachometer to have Maximum Revs. other than changing for a Higher Gear?

  1. Wheel Slip;
  2. Gear not properly selected;
  3. Gear brake band defective;
  4. Gear E.P.V. defective;
  5. Rubber hose to gear defective;
  6. Drain plug missing from under gear piston chamber;
  7. If No. 4 gear, clutch plates may be broken or slipping.

How would you deal with these defects?

  1. Lose revs. and use next higher gear to reduce tractive effort until slip is corrected, then change back down.
  2. Lose revs. and select gear properly.
  3. Miss that gear but if possible isolate that engine and final drive until gear can be toggled.
  4. According to circumstances miss that gear, or if practicable isolate both engines and final drives.
  5. Miss that gear or, if possible, isolate that engine and final drive.
  6. As above.
  7. Isolate that engine and final drive as gear will be in neutral when coasting.

How would you tell a defective Brake Band or defective E.P.V.?

Switch tachometer over to other engine, if that is at maximum, E.P.V. defective.

How would you toggle Gear Brake Band?

Obtain plenty of air, stop engines, engage deadman's, engage defective gear about twenty times, pausing 2 seconds each time. Although bands are automatically adjusted it is advisable to toggle gears 1, 2, and 3, once a turn, engaging them about six times.

What would cause maximum revs. in all gears?

Teeth broken off dog; Spline collapsed; Final drive isolated; Propeller shaft broken; Hardy Spicer couplings uncoupled; Loss of oil from fluid flywheel; Electrical connections from deadman's to gear selector not being made; Insufficient air to operate gears.

What would cause Fluid Flywheel to heat?

Loss of oil through defective gland, or through bad driving, e.g., driving with revs. below 1,100 causing greater slip in flywheel. At 1,800 revs. flywheel torque is at its maximum 2% slip, 1,100 revs. slip is 7.5%. Another cause is standing in gear with the brake on.

What would cause intermittent Black Smoke at Exhaust?

Piston wiper rings defective, improper operation of injectors, improper valve timing, dirty air intake filter.

What would cause continuous Black Smoke?

Fuel pump coupling bolts broken, unsuitable fuel oil, or engine overloaded.

What would cause higher reading in Engine Sump?

Water entering from cracked liner, or defective gasket. Fuel oil entering past defective piston rings, or loose dribble pipe unions on BUT/Leyland type engines.

What would cause whitish evil smelling Exhaust Smoke?

Vaporized fuel, as when engine is started from cold, or engine out of tune.

What would cause a Loud Knock on Engine?

Worn big end or little end bearings, or main bearings, fused piston head, water in cylinder.

What would you do if you could not stop an Engine from the Cab or Local Stop Button?

A.E.C. engine, push shut-down solenoid up by hand. BUT/Leyland engine, lever shut-down solenoid up (from over top of radiator) by using handle of isolating fork. If unable to stop engine this way, close fuel cock; it will take about 12 minutes to stop engine idling, 3 minutes if throttle is opened.

How do you tell Train Pipe from High Vacuum Pipe?

Train pipe is always situated on R.H. side when looking at front of car and R.H. side when looking at rear of car.

How do you destroy High Vacuum for Uncoupling, etc.

Destroy train pipe vacuum, release deadman's and place brake handle in the 'OFF' position.

Suppose when starting engines you had only one bank of lights?

Go back defective side and examine Jumpers.

How many Jumpers can be worked with?

There must always be two outside jumpers (white), but there need be only one inside jumper (black). Outside jumpers are control, gears, forward or reverse, throttles. Inside jumpers are lights and deadman's.

What is a simple test for seeing if Battery is low?

Switch on cab lights, then press start button and notice the amount of dimness in lights.

Engine Light goes out whilst running?

On single power car unit only, switch tacho over to check engine has stopped. Press starter button to see if it will restart, try 3 times with a 10 second pause between, check bulb. When it is next convenient try to start locally, if unable, isolate engine and final drive. Probable causes as for, "Engine will motor but not fire, etc.".

Why 10 seconds pause before pressing Starter Button?

To allow engine to stop, motoring so that starter motor pinion and starter ring will not be damaged.

Engine light goes out when throttle is closed but illuminates when re-opened, i.e., engine running?

Defective lubricating oil pressure switch for lights, situated on top of the engine.

Engine light goes out just before coming to a stand, and again when gear 1 is selected?

In this case engine has stopped. Can be caused by engine idling revs. being too low, causing lower revs. in gear 4 just before coming to a stand, and not allowing lube. oil pump to maintain pressure on shut-down pressure switch situated on top of engine, or could be defective shut-down pressure switch. To overcome this, and save repeated restarting, when running into station at about 8 miles per hour go into neutral, this will take load off engine and maintain idling revs. sufficient to maintain pressure Before starting away engage throttle 1, this will increase revs. from idling by 200 r.p.m. but still allow pump to maintain pressure.

Another cause of engine stopping when throttle is closed is hot oil, causing loss of viscosity, which is brought about by broken fan belts or drive or blocked radiator grilles not allowing air to be drawn through.

What does Air and Axle Lights mean?

That both final drive dogs are in mesh, and there is sufficient air pressure, 75 p.s.i., to keep them there and operate pressure switch.

How do you know Dogs have reversed?

Always notice axle lights go out and then illuminate. If lights fail to go out that car has not reversed, possibly E.P.V. sticking open in former direction.

What would be the consequences of this if it was not noticed?

If set consisted of 2 power cars, set would not move, if more than 2, set would move with throttle open; road wheels would be turning propeller shafts in the opposite direction and drive through free wheels to driven members of flywheels which would eventually overcome the driving members of flywheels, stop engines, and drive them in reverse, causing them to seize.

Suppose Engine had stopped and it was necessary to reverse to clear line. How is Axle Light got in?

Owing to the fact that engine has stopped, propeller shaft will not rotate to put dog into mesh, so, therefore, axle light will not illuminate. To get light in, move car about 6 inches. Road wheels will now turn bevel gear and allow dog to go into mesh, and make electrical contact to illuminate light.

Suppose when changing ends you could not get an Air and Axle Light in with Engine running?

Notice if sufficient air, reverse a couple of times, if still no light, proceed to other power car with C.I.S. and reverser, switch in and put reverser in Reverse, light should illuminate, remove C.I.S. then remove reverser. Proceed back to leading cab knowing that Dogs are in Forward gear so alright to proceed. Possible cause defective bulb or loose connections. It is a good practice, before changing ends, to select direction before vacating cab.

Suppose when standing idling, Air and Axle Lights go out?

Probably defective unloader valves, i.e., not resetting at 80 p.s.i.. This is noticed because compressors are not working so fast with engine idling.

Blank off defective unloader, if unable to do so use some more air by reversing, this will allow spring to re-set unloader; this is better than revving engines.

Suppose, whilst running, all Air and Axle Lights go out?

Reduce speed to 25 m.p.h. (this failure is generally caused by an air leak), proceed, watching air pressure gauge to see if it falls, (if it drops below 60 p.s.i. gears will not operate), if it holds, clear section, if it falls, stop and close cocks between coaches. Good cars' air pressure will now rise and their axle lights illuminate, defective car's axle light will still be out. When in protection of signals, apply hand brakes, stop engines, remove reverser, lock doors, proceed back to defective car, start engines locally and find leak. If unable to remedy,isolate both engines and final drives, sufficient air should be left in the primary chamber, (held by diverter valve), to do this, if not, isolate manually. If unable to isolate, proceed at 25 m.p.h. and back in the wrong direction at 5 m.p.h. to clear line.

This defect, on a single power car, could be caused by defective unloader valve.

Suppose you had an Air Failure on Leading Car?

Shut air cocks between coaches and proceed out of the section at reduced speed. Have Guard in next power car to blow the horn; drive from leading power car. If unable to remedy defect in protection of signals, isolate both engines and final drives; change cars as soon as possible.

Suppose you had a Complete Air Failure through whole of Train?

After stopping engines and locking up, etc., get assistance with a W.L.O. When assistance arrives couple up, also vacuum pipes; isolate all Deadman's and A.W.S.'s; if unable to isolate final drives, or if it is more practicable to leave them in for quickly clearing the line, instruct assisting driver not to exceed 25 m.p.h.; back inside 5 m.p.h. If better for quicker clearing of line, and it is possible to isolate final drives, isolate them and treat cars as coaches.

Running along the road Vacuum suddenly Destroys?

Immediately close throttle, lap brake, gears in neutral. When at a stand call Guard on buzzer. While he is coming apply handbrake and stop engines, then ask him if he has applied setter; if not, has P.C.V. been pulled. While he is finding out, go back and examine A.W.S. flags and isolate Deadman's. If cord has been pulled, proceed back and protect according to rule. When Guard calls you back on the horn, leave the three detonators down and pick up other two, inform signalman in advance, and obtain three more detonators from him to replenish canister. If cord has not been pulled and vacuum can be recreated, it must be a Deadman's defective, so book all isolated Deadman's to be examined. If vacuum could not be recreated after previous examination, it must be a vacuum leak proper, so part train pipe behind first car and place on stopper, test, if vacuum correct, and there will be sufficient brake power, pull brake release cords on rear cars and proceed at not more than 15 m.p.h. to clear section; Guard to give assistance with handbrake if necessary. When testing, engines must be running.

Suppose you had a Vacuum Failure on Leading Car?

Disconnect vacuum pipes between cars and replace on stoppers, isolate both engines, pull brake release cords, propel from next power car. Guard in front to transmit signals, etc., speed not to exceed 15 m.p.h. to clear line, and put off at next convenient place. If necessary, engines can be left running if a heavy gradient is to be encountered.

Suppose you had a complete Vacuum Failure through whole of Train?

After locking up, etc., get assistance with W.L.O., couple up shackle only, pull all brake release cords, Driver not to exceed 15 m.p.h. to clear line,you and Guard to stand by handbrakes in case assistance required in stopping.

Running along the road lose an Air and Axle Light, also a Brake Application?

Electrical failure, on car indicated, causing Deadman's to operate. Close throttle, lap brake, remove reverser, apply handbrake. Go back to car indicated and isolate Deadman's valve, back to leading car and regain control, proceed at 25 m.p.h. to clear section. In protection of signals, isolate both engines and final drives in manner prescribed for electrical failure. It is possible that an electrical failure would not be noticed until speed had fallen to below 17 m.p.h., i.e. when generator stops charging.

Running along the road lose Power and control, all Panel Lights out. Deadman's operates?

Electrical failure in leading car. Close throttle, brake into lap, remove C.I.S. reverser, apply handbrake, isolate Deadman's. Take C.I.S. to next power car, insert and switch on, back to leading car, insert reverser. All lights would return except leading air and axle light. Proceed at 25 m.p.h. to clear section in protection of signals, isolate both engines and final drives as for electrical failure.

Suppose you could not Regain Control at Front?

After inserting C.I.S. in any other cabs available I should assume that leading desk had failed, so I should go back to the most suitable cab for observing signals and see if I could get control there. If not, try other cabs. When control was regained in one of the cabs, put Guard in front and propel at 15 m.p.h. to clear section. Put car off at next convenient place. It is a remote chance that you would not get control in one of the cabs.

Electrical Failures in Leading Cars

With certain electrical failures it is possible, after isolating Deadman's, to still be able to control rear car without taking C.I.S. back. In other cases it is possible to regain full control after taking C.I.S. back, so it is perhaps wiser to take C.I.S. back and possibly avoid isolating.

Suppose you did have Complete Electrical Failure?

Take out C.I.S. and reverser, apply handbrakes, stop all engines with shut down solenoids. Take W.L.O. and fetch assistance, when it arrives, couple shackle and train pipes, isolate all Deadman's and A.W.S. Instruct driver not to exceed 25 m.p.h. and back inside at 5 m.p.h. According to circumstances prevailing to clear line quickly, act as above, but, if more delay would be incurred by not isolating, all engines and final drives can be isolated and cars treated as coaches.

Suppose assistance was a DMU of same type?

If vacuum system is alright both vacuum pipes can be coupled, control jumpers can be coupled if defective engines and final drives are isolated.

Action when Firebell rings?

Notice which engine from panel (light goes out). Stop train in a suitable place, stop all engines, apply handbrake, remove reverser. Take fire extinguisher to affected car, see if automatic fire bottle has operated, if not, operate it by pressing flame switch and, if necessary, use hand extinguisher. When fire is out isolate that engine and final drive, tear tag off fire control panel and reverse 2-pole switch; this extinguishes red light, breaks engine starting circuit, stops bell from ringing and brings thermostat into circuit over fluid flywheel. Should a second fire occur on this engine the fire bell will ring again and hand extinguishers must be used as automatic extinguisher is not available.

Suppose when changing ends you had a continuous A.W.S. Siren?

This is generally caused by contacts in the shoe moving as car has passed over ramps in the reverse direction. Isolate A.W.S. with flag until the first ramp in the right direction, this will reset contacts in shoe.

Suppose you had a continuous siren which you could not isolate?

This is caused by the A.W.S. emergency valve sticking up. The valve is situated under the desk on the R.H. side, and on some cars the spindle can be seen protruding; if it is possible, push it down. If unable to push down, remove pepper box and blank with a coin, or wrap a plastic food bag round it; vacuum can now be created but a leak will be noticed in lap If siren cannot be sealed enough to create vacuum, treat as a vacuum failure on leading car.

Suppose you have a higher train pipe vacuum in one power car than the 1other?

On leaving the higher car to drive from the lower, I should pull release cords on the brake cylinders, proceed to lower car and apply handbrake, then pull release cords on cylinders, recreate vacuum and proceed. The reason being is that the feed valve in the cab driving from, controls the amount of vacuum to be created in the train pipe, so, if brakes were not released they would drag. Book whichever feed valve is defective.

Suppose Train Pipe Needle equalised with Reservoir?

Punctured diaphragm of feed valve. Release brakes with cords, recreate vacuum to 21" and lap; keep eye on train pipe in case of leak.

Suppose after relieving a set, vacuum leaks or recreates in lap position?

Could be a brake handle left in one of the cabs, or a brake valve turned when handle was removed, leaving valve towards 'on' or 'off'.

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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