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Take the locomotive off the track.

With the power on, press down on the contactor and see if the gate goes all the way down.

The mechanism may need servicing. See here for a parts view of the 252 Crossing gate.
http://pictures.olsenstoy.com/cd/accs/acc252p2.pdf

The bottom plate and coil assembly may have a sticking plunger. Disassemble the gate and clean all parts with Naphtha to insure clean sliding and moving surfaces.

Sometimes the plastic core of the coil gets slightly bulged due to heat buildup from a prolonged steady 'on' state, causing the plunger to bind.


Larry
 

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The plunger should slide out, fall out on it's own if held upside down.

That's how the mechanism works. Energize the coil and the plunger's steel bottom is pull up by the coil's magnetic force. The non-ferrous brass top shoots up and hits the cam on the gates axle to lower it.

If it's stuck, that's a problem. Pull it out, twist it, yank it, it's just a smooth rod. They you need to see why it's binding.
 

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The core of the solenoid is plastic. If the coil overheats, it will expand, jamming the plunger. If that happens, remove the plunger and get a twist drill the size of the plunger and ''drill out" by hand the coil so the plunger is free to slide again.

Larry
 

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The core of the solenoid is plastic. If the coil overheats, it will expand, jamming the plunger. If that happens, remove the plunger and get a twist drill the size of the plunger and ''drill out" by hand the coil so the plunger is free to slide again.

Larry
Huh, I have a crossing gate with a busted cam. But never could identify which one. Apparently there are two different cams and I could never identify which cam was the proper replacement part. It's definitely pre modern era as I know the source of the gate.

553745
 

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One of the issues with all these coils is the amount of voltage and length of activation (enough to melt the inner plastic). As I mentioned before, one of my gates has a broken cam - from the plunger violently smacking it to lower the gate. So I did some experiments to see the minimum voltage required to activate the gate.

 
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