I picked up a Marx Western Pacific 901/902 E-7 set at a garage sale. The bodies are in beautiful shape. It was missing the 2 power truck plastic side frames and one horn. I got them from Robert Grossman. The set looks great. It runs fine but drops dead or reverses itself on switches or suddenly reverses itself for no reason. I have never owed a Marx engine. I assume that the reversing unit need servicing. Any advice on what to do would be helpful. Feel free to contact me at my email address hocustom@aol.com. Thanks
In my own experience, Marx reverse units are very sensitive to crud, especially if they've been used or stored in less-than-ideal conditions. The first fix I always try is to locate the reverse unit and spray electronic contact cleaner in it, then put the locomotive on the track and run it, operating the reverse unit frequently to flush the debris out. Repeat as needed. [NOTE: Many contact cleaners contain lubricant. I recommend NOT using them, as the lubricant will just attract more dirt. I only use straight cleaners, with no lube added.]
For me, that's what works 80% of the time. Only in stubborn cases is disassembly needed.
Of course, all this assumes that you've already checked the obvious trouble spots, like dirty wheels, brushes, center-rail skate and commutator.
Congratulations on finding an F7 set in good condition. They're usually pretty badly beaten up.