Saw your query and decided to try and get some answers for you. I contacted Karl Crowther who supplied the following information which mighty help.
If you are able attend expoEM Spring at Bracknell and he will be there and could possibly advise further.
Regards Steve Young – Newsletter Editor
I think you may need to be careful here as the axle sizes in some of these Bachmann diesel models vary depending on which version it is. The early ones had an un-driven trailing axle with 3mm axles, with the leading and centre driven axles having 2mm axles.
I know that the Class 40 was later revised to have all axles driven on 2mm axles, but not sure if this also applied to the Peak
The Alan Gibson catalogue lists a conversion set for the Bachmann Class 44/47 etc. which has 4x 2mm axles and 2 x 3mm axles, so would be appropriate for the ‘early’ variant.
To be sure you’d need to get the wheels out of the model and check the axle sizes (or at least see if the trailing axle in each bogie could be rotated by hand, which of course would mean it was non-driven, and therefore presumably on a 3mm axle).
And suggest a phone call to Colin Seymour at Alan Gibson who I am sure would be able to offer further advice.
Once you know the correct axle arrangement, the actual conversion would be pretty straightforward.
One more thing.
Ultrascale do conversion sets for the Bachmann 4-axle drive Peak – again with a 3mm non-driven axle. They do this in both the ‘full’ set with the gears on the axles, and also the economy version where you just get the wheels and axles, unassembled to use the model’s original nylon gears.
Maybe the Peak models never progressed to having driven trailing axles (which they did on the 40 and 47).
What confuses me is that Ultrascale also list an ‘original’ Bachmann Branchline Class 46, which has 2.6mm powered and 2.0mm non-powered axles. I guess this is the ex-Mainline one the enquirer is referring to and therefore not the one they want.
So again basically you will need to determine what axle sizes the model in question, has.
Hope that helps.