Large Scale Central

Bachmann spring-plunger wheel pickup problems (2-4-2, 4-6-0)

My pal Tim landed me with another older Bachmann 4-6-0 for some mechanical refurbishment. It wasn’t in bad shape, apart from the plug-in wheels falling off and the collar on the blind drivers being cracked - nothing a little glue couldn’t fix. Here’s the wheels after I yanked them off; it’s a “gen4” version with a big final drive gear.

When I got it back together, I did a continuity test, and (as usual) the wheel plunger pickups weren’t working. I decided it was time to figure out what was going on.

The plungers are obviously behind the wheels, so they were readily accessible. I hadn’t noticed the small screws.

They are very small. You need a decent very small screwdriver to get them out and put them back. Make sure you are doing this on a cleared bench so when you drop one you can find it. [A 1.2mm bolt can be substituted - ask me how I know.] Here’s my Wiha ratchet set screwdriver bit helping to get the back plate off.

George Schreyer’s Technical Tips (you do have George’s Tips bookmarked, I hope - even though he hasn’t updated them for years, it is a treasure trove of info about the older models,) says “The Bachmann contacts heat under heavy load and the spring looses tension. On this engine, a spring actually melted the contact housing.”

I haven’t seen a melted one yet, but clearly the springs don’t work. You can see in this photo that the spring is hiding in the housing. It is supposed to make good electrical contact with that metal back plate. One would hope it might try and spring out when you take the plate off - no such luck.

So the easy solution for a few more years of use is to extend the spring so it works. Gently pull it apart until it fits in the housing and protrudes a little.

Then put the cap back on. It’s fiddley, but I found my tiny screwdriver would hold the screw while I used my nails to hold the cap in place, then pushed the screw in to its hole.

The caps are supposed to be soldered with wires to the motor. In that prior photo, where the cap is lying on the bench, the wire at the soldered joint has already broken.

When you have all the pickups back in place, a quick wipe with fine emery paper or similar wouldn’t hurt.

A couple of updates following the completion of the project.
There was a big blob of glue holding the wires away from the gears, which prevented me from lifting the rear pickups out to fix the springs. I pulled the 2 wires I needed out of the glue.

With the wheels back in place, I was testing the pickups (worked great!) I then noticed that the new spring pressure had pushed one of the wheels out of its sleeve! This particular loco had been taken apart many times, so the wheels were loose - hopefully yours won’t be.

Nice writeup Pete. Reminds me of our fun with the nightmarish Bachman center cab diesel and the Heisler, both with that hateful gravity something or other pickup pins…