Rich,

I looked at the online diagram after someone in another forum mentioned it and discovered something odd: mine is not an all wheel drive unit ! There's space for a driveshaft in the front but the motor doesn't even have a connector on the motor shaft for one and there's no gearbox in the front truck assembly. I located the paperwork that came with the engine and the diagram has it as a single-truck drive also. This was part of a set distributed by "Great Planes Model Distributors Company" that had a powered GP-40, a GP-40 dummy and a caboose. So now I wonder if Bachmann made single-drive units just for these sets ?

I am now considering replacing what's in there with a new motor & powered trucks set - there's room in the body for them.

I have a new-old-stock Bachmann GP-40 that has a perplexing problem with the powered rear truck assembly. I inherited this unit from my dad and it looks like it's either never ran or has been run only a few times. I ran for a minute and then it lost drive to the wheels on the back/powered truck. I took it apart and there was a lot of lubrication oil on the entire drive shaft assembly. It took several cleanings until it would stay together; but now I have a new problem: the front axle of the drive truck seems to be slightly higher than the rear axle and the engine constantly derails. I tried taking it apart and reassembling it. If I get it loose enough that it sits level, when I stop the engine, the rear axle on the drive truck almost always derails to the right. If I tighten up the assembly to where the truck sits level, it's too stiff to navigate the curves. If I run the engine in reverse, where the powered truck is leading, the engine runs fine with no derailments. Any idea what I've done wrong and/or can remedy the problem ? Should I try replacing the entire drive truck assembly ?