Mysterious fault

[petertg]

I am posting this request for help here because I have not found any other suitable place.

I have a Bachmann Class 150 DMU and when it reaches this turnout (obviously with the points set straight, not for the curve as shown) in the direction of the arrow, with the power car driving forward I have trouble. If it is going at some speed it derails, at a crawl it provokes a short. If the power car is pushing (i.e. going in reverse) or if the DMU is going in the opposite direction (in this case it doesn't matter whether the power car is pulling or pushing) there is no problem. None of the other locomotives I have suffers any problem at this turnout. Can anybody suggest a reason for this anomaly? I have a further 14 turnouts on the layout and the DMU has no problem with them.

[Ray H]

It may help if you could determine exactly where on the point each happens, the short maybe easier to determine than the derailment. You do need to try to ascertain which wheelset on which bogie of which vehicle derails?

 

Has this always happened?

[petertg]

This has always happened. The short is obviously caused by the leading bogie of the power car, as yet I cannot say which wheel set. I had thought that the derailment actually occured at a curve upstream from the turrnout but, since a long straight follows, the unit continued running up to the turnout where it finally jibbed. It is rather hard to get a close view of the track from the side, since the curve is at the entry to a station with its platform and side wall and the view of the turnout is hindered by the columns of the overpass. Also my eyesight is not good where dark objects are concerned. I will continue investigating.

[johnb]

Without knowing the precise location at which the issue occurs it is a bit tricky to know just what is happening. However one possibility is that with the leading wheelsets being 'pushed' it is possible that the back to back measurements of one of the leading wheel sets is slightly out. The push mode is enough to force the wheels to one side, whereas being 'dragged' it takes a very slightly different path. As for other points being OK, maybe they are slightly less worn or of a different manufacturing batch.

 

If after a short occurring you push the unit further on does it derail anyway? If so then first look at the back to backs, then the point level and wear.

 

John

[SGJ]

do you have a camera that might video the problem ?

[peter220950]

Can't see from the photo, but is there an insulated rail joiner on the connection between the two point frogs?   - Not sure if it's relevant but depending on how the frogs are wired might there be an issue there? - if there isn't an insulated joiner it might be worth sliding the fishplate back to give a rail break then try it? - That wouldn't explain a derailment, but the number of times I've tried to solve a problem and found there were actually two different ones..............

 

As a second suggestion have you checked the back-to back measurements on all of the axles?

[RFS]

If it shorts at slow speed and derails at high speed then I would say it's a back-to-back issue.  I would run the DMU slowly through till it shorts and then carefully observe exactly where the wheels come to rest.

 

I would suggest that the problem occurs just beyond the frog in the picture as we look at it.  The back of the LH front bogie wheel is touching the rail that is curving into the frog. I've had that problem but with a code 75 Electrofrog double-slip with the offending loco being an early Hornby West Country, produced at a time when Hornby's back-to-back setting was 14.2mm and not the 14.5mm it now is. Correcting that solved the problem.

[RAF96]

I would concur that back to back being out of spec is the likely culprit.

[petertg]

I have checked the back-to-back on all the wheel sets of both bogies and, unless I am mistaken (not impossible) it is 14.2 mm. I have not had the opportunity to check other points kindly mentioned by the contributors.

[RAF96]

Try 14.5mm

[petertg]

I have spent a couple of hours this afternoon investigating the problem and I think I have found the cause. Close observation led me to think that the chassis of the vehicle was rubbing on the point motor that can just be seen in the photograph because immediately at the exit from the turnout there is a curve to the right which pulled the vehicle over the motor. While i did think that this was not possible, I temporarily removed the motor and finally saw that the front wheel set of the rear bogie was jumping the track when it hit the joint between the straight track and the turnout proper. The rail ends seem to be on the same level but there was a large gap between those rail ends and although I tried to close it a little, there still is a gap so I imagine that the only solution is to relay the track and turnout, something with which I am not at all happy because in the past I had had derailment problems on the curve following the turnout and the track there is a little bit forced. In any case, thanks for all the recommendations and advice.

[Ray H]

I would still tend to favour another cause of your problem.

 

Does the bogie always derail to the same side of the track?

 

Turn the vehicle round if that is possible and see what happens then. Run the vehicle over the place it derails at progressively slower speeds until it doesn't derail and see if you can see what the bogie is trying to do. Better still, get it as slow as you can with it derailing and stop the train as quickly as possible. Have a good look around the coach to see if something is catching where it shouldn't. Is there something hanging down from the underside of the vehicle.

 

What radius is the curve immediately beyond the point?

 

Is the wheelset falling between the two rails rather than jumping off to one side?

 

I haven't used what looks like set-track for a long while. However, my understanding is that its geometry is such that you shouldn't find large gaps between rail ends at joints. Perhaps the alignment of the track is at fault or playing a significant role in your problems.

 

Do both bogies rotate freely on the vehicle even when the weight of the body is pressing down on the bogie.

 

Are the couplings somehow preventing the bogie from rotating?

 

Can you push the bogie over the joint at a good speed and does it derail then?

[Matt]

I had a similar problem with a 150 albeit the problem only occurred going in other direction. I eventually solved by increasing the gap between the 2 cars ever so slightly and never had a problem since. Simply slackened off the joining bar a little in the socket. I could never see why was happening but happened every time on same stretch of track and only unit or loco ever to derail here out of a very large fleet. Since the mod have managed to run in for 1 hour with no issue. Model was an early regional unit. My scotrail unit didn't show same issues. Given this I changed entire bogies between units to no avail until I happened on the solution!

M

[petertg]

My DMU is the Regional Railways Leeds-York version. I would say that my recent tests have been performed with the power car alone but derailment also happened with the two cars connected. I have tested with the vehicle in reverse, I have turned it round and run it backwards and forwards, but derailment only occurs when running forward in the direction of the arrow in the photo and the leading pair of wheels on the rear bogie jump to the right. The curve is first radius. I will have another session with both cars coupled. I have a problem with rerailing in that with my fingers as they are I cannot place the locomotives easily on track without the rerailing accessory and there are only two places on the layout where that can be used correctly and both are on the opposite side to where the fault occurs, so every time derailment occurs I hve to take the material round to the other side of the layout to start again.

[Phil S]

To assist rerailing at other locations - can you not create a permanent fixture in the track akin to a Level Crossing or Rerailer track - eg in suitable tunnels or where a walkway across might be used.

[Ray H]

I am beginning to suspect that the problem may be the 1st radius curve and the close coupled unit based on what Matt has said about his experience.

 

I don't know how easy it is to ease the coupling distance between the two vehicles of the unit but I'd suggest that might be a good first port of call.

[petertg]

The problem is not caused by the close coupling of the cars, since the derailment occurs when the power car is running alone. Yesterday I tried out other vehicles and observed further anomalies. In the first place, I would say that the Class 150, apart from its annoying habit of derailing under specific conditions, can run around the circuit without problems and only hesitates at one point when running at low speed. It is fitted with an ESU decoder. However, my Class 108 DMU (with an Uhlenbrock decoder) seems to lose the dcc signal at various points around the track, as do other vehicles at the same points. The fact that the 150 does not hesitate at these places leads me to think that a dirty track is not the problem. Also my Stanier 2-6-4 tank (with a Hornby decoder) did a funny thing: it suddenly stopped, went into reverse for a few centimetres and then started running forward again. In the past, the Class 108 DMU has several times stopped and reversed the lights, but never started running backwards. While I do not have every single track piece connected to the dcc bus, some of the apparent signal failures occur close to where there is a conection. I must clarify that my connections are hybrid: a lot are by droppers, but there are also several with power clips (all suitable for dcc use). I assume that all this means that I have to revise the whole track layout. Apart from this, I still have to give a further three locomotives a run around to see where they object.

There are only two possible places where the rerailer can by properly placed.

Anyway, we are going away for a fortnight's holiday next week so I shall have to forget about these probems for a while.

[Phil S]

Just to double check: You have just mentioned the use of Power Connectors (Commercially made type): HAve you double checked these are for DIGITAL CONNECTION anand not ANALOGUE? --- the Analogue versions INCLUDE a CAPACITOR to suppress electrical interference, but the the DIGITAL versions do NOT:  If any have the capacitor, either remove them, or cut and separate at least one Capacitor lead, so that it is no longer in circuit.

 

You rejected the idea of dirt on the track because (only) the ESU decoder continued at the suspected pplaces: it may be somply because the ESU decoder either copes with a lower (track) voltage better, or has more resistant processing /Stay alive built in.

 

Suddenly reversing is a sign of receiving corrupted data, or lack of.

IF you try a loco with a stay alive capacitor fitted, and run it over the same track, you might help identify what the actual cuases of the problems are.   You mention multiple droppers: these should not CAUSE a problem, but help eliminate a potential problem. They will not cause 'phasing' errors unless reversed 180 degrees! ... which brings me to mention, as a test of conductivity .... have you tried the 'Coin Test' .... a coin placed anywhere on the track should trip out the Controller, as sufficient current should be able to flow through the track to ensure it exceeds the protective cutout setting of the Central Unit/Booster.

[petertg]

I said in my last post that all the power clips are appropriate for dcc use (I am aware of the capacitor problem). I have to-day tested a further three locomotives, two fitted with stay-alive capacitors (both with Zimo decoders) and the other one just with an Uhlenbrock decoder and they did not display in general, the problems I had yesterday. The three locomotives I tested to-day had no problems at all at high speeds, running in both directions forward and reverse, and, in fact, at speed levels 1-3  they even passed over spots which caused problems to the other vehicles. I have, however, located two or three spots which need attention. One has nothing to do with power. I have discovered that certain vehicles with low clearance are rubbing on a piece of wood I have placed between the rails on a scratch built level crossing, which brings them to a stop.

I will try the coin test again, but I believe that in the past it worked as it should.

I shall just have to keep at it until (hopefully) I iron out all the problems

[RAF96]

"certain vehicles with low clearance are rubbing...brings them to a stop"

 

 

I have a Bachmann Jinty that grounds out and stops on a Hornby uncoupler and also at some barrow and level crossings. The only answer was to file away the axle spring mouldings for adequate clearance. Ruins the model but improves the running no end.

[petertg]

I tried the coin test on three separate places, just to be sure, and each time the controller cut out immediately. As far as the rubbing on the ground is concerned, it will not be hard for me to file down the wood in the middle of the track. I am also coming to the conclusion that some of the problems are due to the vehicles and not the track, notably the Class 108 DMU which has now also developed a fault in that the headlights and headboard of the dummy car do not light up when it is selected to run leading. When trailing the red lights and the headboard do light up. Any suggestions to cure this would oblige.

Any way, I have had to pack things away until the end of the month in view of our impending holidays and preparations to clear up odd jobs that have to be done before we go.

[petertg]

I am now back from the holiday (we had a very good time in Portugal and something similar to a crash course in Portuguese) and with a digital caliper that I picked in a Lidl while I was away, I have checked the back-to-back on the 150 power car and have discovered that the offending wheel pair is wider apart than the other three pairs, namely 16·46 mm in comparison with 16·25 plus/minus 0·001 mm, which I assume may be the cause of the derailment. I am now faced with two problems, namely: 1. how to close the gap without damaging the model, in view of my lack of suitable tools (any advice will oblige), and 2. I cannot check the track width at the crucial point at this time because my layout has come crashing down to the floor. I lowered it without placing the trestles underneath because I only wanted to take the model off the layout, but when I pressed the button to send it up again, it came down, pulling the take-up roller from the wall. Until I can get someone to help me lift it off the floor and place it on the trestles, I shall not be able to assess the extent of the damage. Fortunately I was alone at the time and, obviously, not underneath it, so no personal injuries were suffered.

[Phil S]

Without changing the actual back to back of the offending wheelset, perhaps you could move that axle to a different position in the unit, to see if the problem moves too ?

 

If it is an unpowered axle, that should be relatively easy - and may perhaps match a wheelset used in someting else you have from Bachmann - if it is a powered wheelset, then it could still be swapped to the other position - but with more trouble .... and during this removal would be a good time to try and change its back to back ...a s long as this can be done without breaking plastic axle insulation or bending the wheel off axis.

 

As it is wider than  the others - is there a small gap showing in the parts of the axle ??    It should be possible, without specialised tools, to create a device for squeezing the wheels together ... a vice if plain ended axles, or with added rings (washers?) to surround the needle point. (Parallel, controlled pressure is required)

 

Another possibility to try - although less likely to be a solution on Bachmann rather than Hoirnby/Lima products, is the effect of extra weight ..... try taping some weight to the roof over the offending bogie to see if it improves running.

[petertg]

To close this topic, I can say that the problem seems to be cured. As a result of the accident mentioned above I had to lift and relay part of the track to repair two disconnected point motors and one was in the area of conflict. I have now relaid the track and the DMU passes perfectly. However, I have not discovered why the derailment occurred. There seemed to be nothing wrong at the joint between the straight and the point where it occurred and only with this vehicle and only in one direction. Thanks to all for your comments.

[The Bigbee Line]

To close this topic, I can say that the problem seems to be cured. As a result of the accident mentioned above I had to lift and relay part of the track to repair two disconnected point motors and one was in the area of conflict. I have now relaid the track and the DMU passes perfectly. However, I have not discovered why the derailment occurred. There seemed to be nothing wrong at the joint between the straight and the point where it occurred and only with this vehicle and only in one direction. Thanks to all for your comments.

It's good you solved the problem.  Nice to see a good ending.