strange issue with Hornby 3800

[The Fatadder]

Hoping for some advice with a troublsom loco 

 

I have a DCC Fitted Hornby 3800 class which refuses to run properly on the track.  Today I cleaned the wheels (and the track), removed the body to check for any obstructions and then gave it some running on the rolling road.

 

On the rolling road it runs beautifully, at slow speed it will crawl along on step 1 and at faster speeds it is equally smooth.  However as soon as you take the loco off the rollers and put it onto the track, its a different loco.  It refuses to start on its own, it judders forward and refuses to move on low speed steps.

 

I cant understand it, as far as I can tell there is minimal difference between running on rollers and running on rails.  I cannot understand why it works so very well on the rollers yet so badly on the track.

 

I am running out of things to try, so would welcome more advice. 

[Clearwater]

Couple of suggestions (that I'm sure you've tried). Do other locos work fine on that bit of track? Have you tried the 3800 on other bits of track? Perhaps worth trying the loco on a wholly separate piece of track as a test?

[RAF96]

On the rollers there is no resistance to running, whereas on track the loco has to drag its weight around.

I had a tired ringfield motored Class 56 which also ran well on the rollers but would not run on the rails.

Rob