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Any suggestions! please. My Inter City Hornby coaches when running, have an annoying show of a fast "pull-push" effect. Couplers are of Hornby originals, while the Heljan diesel locomotive have the modern EM type couplers fitted.
Coach wheels have been inspected and cleaned thoroughly and show no problems, spin freely when rotate by hand. Track itself is cleaned regularly with no noticed irregularities.

 

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Britho, thank you for your help. All coaches were fitted with Hornby new steel wheels. I agree that wheels you mentioned where a nightmare, certainly a quick replacement was order of the day.

 

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SRman - if you imagine the coach coupled to the diesel engine, speeds up and slows down in slow motion, is the visual effect that I am experiencing.
Due to size of my layout, I only couple one coach to an engine, giving me the above mentioned effect.