Hornby HST, no reverse

[hedgeaf]

Hi,

 

Have got a modern Hornby HST out of the loft that I planned to sell (doesnt fit with what I run), but on testing it am having problems. It's a DCC model although only ever run on DC as my layout plans have never developed as hoped (indeed this is a little downsizing).

 

It runs great forward, but on switching to reverse you get a couple of small judders (with red lights on)  and then it dies (lights out).

 

- Removed the fan to prevent that causing extra load on the motor  (this is the older single fan type - I remember it being intermittent in working although I understand that is common)

- Lubricated the axles and the motor to bogie ball joints. 

- No sign of any broken wiring connections.

- Swapped decoder with that of the dummy power car.

 

No change. 

 

There was a some white gunk (grease of some kind) around one end of the motor which had sprayed on the inside of the loco. Is this a sign of the sealed motor having failed and this has come out?

 

I get the impression it is trying to move but failing and then perhaps the overload is cutting it out? but why would it work fine in one direction not the other, as I can see it, the motor drives both bogies 

 

Any suggestions - I'm leaning towards the motor but its not had a lot of use so that seems odd. 

 

cheers for any help

 

 

[hedgeaf]

Interstingly, if I whack the power straight up to 2/3rds, then off it goes and runs quite happily. Just judders at low power. 

 

It's a DCC loco on DC, and a fairly cheapo controller which may be the reason, but why one direction so much better (fine control at all power)?

[34theletterbetweenB&D]

The movement symptom you report in reverse, 'judders a little and stops', is one that I would most associate with a probable mechanism fault typical of 'centre motor drive to both bogies' mechanisms.

 

Explanation of the symptom . Because both bogies carry much the same weight and are worm driven, if one drive shaft stops turning then the bogie with drive tries to move the loco, but the stopped bogie acts as an effective brake.

 

Cause. Somewhere in the shaft drive line a push fit component - most usually the plastic plug in the flywheel - can slip, and that leads to no drive to the worm. The slipping frequently is unidirectional when first observed, and will not always happen either. As wear from the slipping builds up, it becomes more frequent.

 

Easy diagnosis. Put some felt pen dots on all the wheel rims. Run the loco, and then you can easily see if one bogie's wheels are not turning when the trouble arises.

 

Fix. A little cyanoacrylate to secure the slipping component.

 

There are other potential causes of course, but this one is the most likely in my opinion.

[hedgeaf]

Hi - many thanks for the reply, I will give the pen marks a go and see (unfortunately a hell of a week at work and off next week so haven't had a chance to come back or try it yet). It is odd that if you give it a load of power it will get going and keep going, drop the power and you end up back at the judder and stop. 

cheers.

[andypops]

Agree with 34 B&D. Have had two of the recent design HST do similar. I didn’t need to use cyano to fix them; I found some thick grease (think lith-moly*) liberally applied to all parts of the gear mechanism did the job. My issue may have been different to yours but the symptoms were identical.

 

* - not sure if Lith-moly is conductive - mine was a non conductive grease for constant velocity joints, as old as the ark and with no label.

 

Ref the high speed movement / low speed nothing, think physics. You’re almost certainly getting a lot of friction at slow speed which you overcome with increased power. As the power overcomes the friction, you get movement. As a proof, if you have another similar HST why not try to run it on the same track at the same time? I bet this one runs slower and won’t catch up.

 

The cause of the friction needs to be sorted as it could cause a major problem. In a worst case scenario, the motor and / PCB could burn out (both fire risks) or the gears could disintegrate (or a drive shaft shear). Unpleasant.

 

As an aside, I’ve found that lights on modern Hornby are a law unto themselves. I have some unchipped locos which if I put on my DCC track either show no lights, both directions or for one (problem child) Class 60 show a red at front only, moving in both directions. I know it isn’t the locos as I have swapped chips into them and they behave fine. Presumably it’s just an issue with Hornby’s PCB on DCC ready locos.

[Pete the Elaner]

It's a DCC model although only ever run on DC

 

 

 

- Removed the fan to prevent that causing extra load on the motor  (this is the older single fan type - I remember it being intermittent in working although I understand that is common)

 

 

Are you sure it is a mechanical issue?

 

It sounds like you have an older DCC fitted model, still with its decoder. If so, this is likely to be an R8215. Hornby discontinued this because it did not work properly.

 

If it was my model, my first action would be to replace the decoder with a blanking plug. If the model then works, throw the decoder away.