R2635 Stanier class 4P goes forward but not backwards

[IanEdward]

I acquired a Stanier class 4P which is DCC ready, I fitted a decoder. It ran well in both directions without the body. With some difficulty I fitted the body it ran forwards OK but not backwards although the motor made a turning noise. I thought it was the decoder so fitted a smaller one. Again it ran well without the body but only forwards with the body fitted. I have cleaned the track and the wheels. Any ideas?

[Chrissaf]

If it runs OK with the body off it won't be the decoder.

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More likely the body is pushing down on something when fitted, that presses against the motor and gear mechanism. Perhaps a decoder wire is being jammed in the works by the body, but moves away from the jamming location when the body is removed.

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This has got to be a mechanical issue rather than an electric one. If you can hear the motor turning in reverse, then the drive must be slipping. The gear blockage may only become an issue in reverse, such that the gear is jammed and slipping, but when going forward what is causing the jam is not present and therefore less drag on the gear, therefore not enough drag to cause the gear to slip.

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Another possibility is that when you had it apart you might have dislodged the motor mount in some way, such that in reverse direction the motor torque lifts the motor and the drive gear moves away from the drive.

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The key thing to note is that you can hear the motor turning in reverse, so as I said before it has to be a mechanical and not an electrical or decoder problem.

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TIP: As this is your very first post, just be aware that the 'Blue Button with the White Arrow' is not a 'Reply to this post' button. If you want to reply to any of the posts, scroll down and write your reply in the reply text box at the bottom of the page and click the Green 'Reply' button.

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See also – further TIPs on how to get the best user experience from this forum.

https://www.hornby.com/uk-en/forum/tips-on-using-the-forum/

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[IanEdward]

Thank you. I'll take it apart again and see what I can see!!  The reason I put in the second decoder was that I thought it may be pressure on something causing a problem. The second decoder is very small with no wires but I'll check the rest.