Having just replaced the magnet in my Wrenn unrebuilt BoB bulleid pacific with a Neo magnet I thought I'd do a haulage trial on my 1 in 28 helix. The Wrenn loco could haul an 8 car train up the helix but could not start it, would keep going with a push start. The unrebuilt modern BoB Hornby loco would just slip its wheels even with a push start would slip to a halt. The rebuilt Hornby BoB could start the train with a little slippage unaided and pull the train up OK.
Conclusions Hornby have managed to imitate life with better haulage of their rebuilt over the unrebuilt. Despite the weight advantage of the Wrenn over Hornby the Hornby rebuilt still has better haulage capacity. So must be down to a better motor and less losses in the transmission. Good to get the Wrenn performing well again though. As an aside I was surprised at the haulage capacity of the Hornby Q1 when I had done trials with that before, disappointed with the M7 though.
Test was conducted with 3 Bachmann bulleid coaches, 3 Hornby mk2a coaches, 1 Lima mk2b and 1 Airfix mk2d. All three locos were running on DCC at @ 18V AC on DVM.
Chris