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I purchased a Lionel Sd70 dummy engine with the idea of upgrading lights and couplers.  The rear coupler opens at random spots on my layout.  This is the only engine which exhibits this behavior.  I also have a Williams Genesis dummy which was also upgraded.

I tried the following:

1. unplugged the electro coupler from the ERR board and it still opened at random spots

2.  I put in a non functioning electric coupler.  It opened at random areas

3.  Put a pin in the coupler so that it would not open.  

Any ideas???

Thanks

   Marty

 

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If it opens spuriously and is not connected electrically, then the coupler is bad mechanically.

I have heard of disassembling the coupler and stretching the spring that presses on the pin.

I have also heard something about putting graphite in the coupler, or on the internal pin, but have no idea how that would stop spurious uncoupling.  Maybe you do that after stretching the spring.

Last edited by RoyBoy

I have taken some of these apart and smoothed all the internal mating surfaces.  This prevents the coupler from "walking" open due to vibration.  A number of years ago, Boxcar Bill had posted his fix, opening them and smoothing the mating surfaces.  I tried it, and it has worked well for a number of these.  Obviously, you have to pull the rivet, do the work, and then reassemble with a new rivet.

Stretching the spring is also a suggested fix.  I'd really replace the coil spring, but I've never found a part number for the spring.  This spring is not the wire spring that actually opens the knuckle, that one is readily available.

Beemer posted:

I just unplugged the worst offender and it ran the last 30 minutes without uncoupling.  So one down.  Glad I found this thread.  I'm going to try the graphite next, sounds easiest.

If it holds with the electrical cable disconnected, then there is an electrical problem where the coupler is spuriously be commanded to open. The fix in the old days was to put a capacitor across the power leads to the coupler. I do not remember the value of the capacitor.

Roy is right, you're looking at the wrong end of the horse!   You want a 1uf 50V non-polarized capacitor, usually the best place to put it is soldered on the back of the motherboard where the coupler plugs in.

Do NOT apply this to later Legacy locomotives with the RCMC control board!   They use DC for the couplers and the capacitor is very bad for their health.  Earlier Legacy with the R4LC still use the AC drive for the couplers, this fix is appropriate for those models.

martind posted:

Guys, the part that I do not get is when I disconnect the coil coupler from the board or used another coil coupler which was totally not wired to anything the coupler would still randomly open???

Marty

Seems a manufacturing defect, the pin is not engaged enough to prevent the knuckle from opening.

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