A while back I reviewed the DJM J94, and came to the conclusion for me that it was a bit ‘meh’, I know, I know, that sayings ‘so last year’ now! The review is here djm-j94 Since then the model has been sitting on the shelf of doom, but working on a small industrial project I thought it may be time to look at it again. Common with the DJM/Hattons 14XX the J94 has a fully geared chassis, so the coupling rods are only cosmetic. Both types have the unfortunate characteristic of ‘cogging’ under load on a descending gradient. This is the J94 (this one) on a 3% gradient youtubeJ94
This appears to be a common issue, I’ve run seven of these J94’s with the same result. I’ve largely resolved it on my 14XX with some open chassis surgery removing part of the drive train, and replacing the coupling rods 14xx-frustration.
Well I’ve decided to try a similar solution with the J94. Initially I removed the coupling rods to no improvement. Next was to get into the chassis, and like the 14XX before it, the task was squarely in the PITA category. If the end game works I’ll write it up! The heading picture shows the model and four gears, those have been removed from the gear train, so it is a simple worm to tower geared drive system.
So the results so far. Under load downhill with no rods, almost imperceptible cogging, there is still some, and that will be due to the mesh of the worm to the top gear.
Uphill with no rods the loco slips, in the original review the lack of weight was noteworthy for me.
Replacing the rods (with originals) the loco again cogs downhill, they’re rigid rods, and climbs with no problem under load. On the flat there’s no difference to when the model was fully geared. Wheels in all cases are self quartering due to square stub ended axles.
Next job is to replace the rods with prototypical knuckle jointed rods and see if that nips the cogging problem in the bid. I hope it does, overall (apart from the mechanism), the models a reasonable starting point for a detailing and weathering project. If you have a flat earth society layout, I suppose it still is…
Albion Yard 
A bit ironic as one of the options is Mog resident on the Pontypool and Blaenavon Railway which has some challenging gradients to say he least!
Isn’t this cogging on descents usually the result of too much fore-aft play in the worm? It might be an easy thing to prove by building up some temporary bearing surfaces either side of the worm.
Incidentally, I’m not expert by any stretch of the imagination!
There’s very limited end float on the worm. The chassis free rolls now less four drive gears and with original rods, so the issue is definitely the worm/tower gear interface. The build of these models are ‘throw away’ they’re not designed or assembled to be easily maintained. I’ll try to get access into the motor housing over the next couple of modelling sessions. Maybe I should just build a flat layout!
Paul, I have too have done something to my DJM Austerity. I removed all the gears, trimmed back the plastic ‘spacer’ arrangement and got much better running from it. Untill something went terribly wrong. I’ll do a blog post later on it.
Well I’ve got four cogs you can have :0)
Hello Paul.
I was talking about this problem with the proprietor of our local model rail shop, and a modeller in his own right, today and he shared some words of wisdom, which followed on from his scepticism about the benefits of a fully geared chassis. In summary it has been tried before by another manufacturer and didn’t work well then.
Anyway, when I mentioned the reported problems when running down a gradient under load, he was not surprised. He said that under those conditions the motor is actually acting like a brake. Consequentially the locomotive will try to run faster under gravity, the motor acts as a brake and the gears are unable to deal with the two forces at the same time, which is not the job they were designed to do.
I’ll stick to my Dapol/NB Models/RT mash-up austerities for EM, Paul. I doubt I’d ever get that running to my satisfaction. Once you’ve done Mashima/High Level there ain’t no going back! 😉
Warley and an RT chassis beckons Dave!