2-6-6-2 troubleshooting help

[Bart]

I am looking for direction on troubleshooting my 2-6-6- 2 steamer.  My steamer was climbing a grade and all of a sudden the back drivers locked up and I can't or don't know how to free them up.  checked directions but can't find any help with this issue. 
The front drivers work both directions but it appears the rear one is locked up?

Bart

[Jim Banner]

It sounds like one of the drivers turned on its axle, causing it to go out of quarter.  This link helps explain what quartering is all about.
http://newsgroups.derkeiler.com/Archive/Rec/rec.models.railroad/2005-11/msg00342.html

Jim