DCC F7A + B speed matching ideas needed

[salpiner]

Hello, group.
I have reset decoders in both units to factory defaults. To test, I MU'd both units and ran each on separate tracks at the same time. Both start out at same very slow speed. Then as the throttle advances, the A unit takes off much faster than the B unit. Any ideas on how I can slow down the A unit to match the speed of the B unit across the entire throttle range?
Thanks for any help.

[skipgear]

Unless Bachmann has put an upgraded decoder in them, there isn't anything you can do other than maybe look for binding in the slower loco. Their basic decoders don't support Vmax, only Vmin (Start Voltage).

Check the slower loco for binding or any odd harmonics or noises that could be causing the slow down. At slow speeds the decoder can mask the added drag which is why they could be matched well at the start.

[salpiner]

Thanks, Tony.
I'll start with just loosening the screws that hold the frame together.

[MrCrab]

Also look for any flash on the worm gear and drive gears on the trucks. Use a gentle hand when removing any that you find with a fine tiny file or a xacto blade. Re lube and break the slower unit in for and hour or so and try mu-ing them again.  If they are still slightly off I like to but the slower unit behind the faster one to buffer any snap the faster unit might cause to the train.