Bachmann Coupler Fix
Helping Bachmann large scale couplers to keep it together.
Bachmann Large Scale couplers are sturdy, inexpensive, and even if oversize, are at least shaped about like the real thing. But they sometimes have a bad habit of uncoupling at the wrong time. Occasionally just taking up the slack in the couplers is enough to cause one of them to jump open. The problem seems to be that the locking pin is too light and lifts too easily when the coupler is shocked. Adding weight helps a bit on completely smooth track, but if the track has any bumps, the added weight often causes the coupler to open when the wheels hit a bump and the weight, along with the locking pin, are thrown upwards.
Our solution is to add a spring that holds the pin more firmly down. Compared to a weight, the spring has a high force to mass ratio and so there is no tendency to lift the pin when hitting a bump. As an added bonus, the spring can extend to form an easily operated cut lever. Installation requires about 5 minutes per coupler and costs less than a dime (and that is a Canadian dime, folks.)
The first step is to drill two holes in the coupler. Well, actually three holes, because one of them is drilled from both the top and the bottom. Drill the upward hole and the downward hole at a point 1/8" forward of the rear of the body and 3/32" in from the side of the body. See the diagram below, keeping in mind that it shows the coupler from the top.
We usually drill the holes with a #76 drill chucked in a Dremel tool, but a pin vice works well too. Drill the third hole horizontally through the locking pin. There is usually a dimple about 1/8" down from the top which makes it easy to start the drill there.
Next step is to bend up a spring. We usually use .015 music wire from the hobby shop but .020 works well too, although you may have to drill the holes a little larger. Cut off a piece of wire 4 inches long or a bit longer. You can cut music wire with hardened diagonal cutters, or with an abrasive wheel in a Dremel tool, or by holding it with two pairs of pliers close together and bending it slightly back and forth until it snaps. Starting at the mid point of your piece of wire, wrap it tightly around a 3/32" diameter rod - the shank of a 3/32" drill bit works fine. Wrap it for two full turns. The diagram below shows 1-1/2 turns, but that is about how far back the music wire will spring when you let go.
Your spring should now look like a spider with one long leg and one even longer leg, with the legs parallel to each other. If the legs are not parallel, fiddle with them until they are. Then bend the less long leg 90 degrees outward at a point 1/4" from the top of the spiders head. Lastly cut the longer leg to make the spider 1-1/2" tall. If you are at all arachniphobic, then forget all this spider stuff and just go by the diagram above.
Installing the spring is a miracle of modern science. Well, maybe not. But would you believe that it can be popped into place, even though it looks impossible? Thread the bent leg through the two aligned holes in the corner of the coupler body, working from the top down. When the eye of the spring (the spider's head) is still an inch or more above the coupler, thread the other leg through the locking pin. The spring will bend to accommodate this. With both ends inserted in their holes, push the spring eye down to the top of the coupler.
Finish off the installation by cutting off the extra length below the coupler (do not cut the leg that goes through the locking pin - it will be your cut lever!) Cut off the extra length, but leave 1/8" or so below the coupler. If you are using side cutters, put one finger over the spring eye to prevent it from being ejected when the cutters snap through the wire. Then bend the extra 1/8" at 90 degrees or a little more, bending it toward the front of the coupler. Lastly, bend over the last 1/4" of the cut lever so that you don't stab yourself and say bad words every time you reach for it. Clint Rigg (member of Puget Sound Garden Railway) suggests slipping a piece of small heat shrink tubing over the cut lever. This stiffens the lever slightly and provides even better finger protection.
The finished product (before adding shrink tubing) should look something like the coupler in the photo below.
Please note that the coupler above is shown mounted on a coupler height
gauge. This is definitely NOT a secret new kind of car for taking kinks
out of straights and curvature out of corners.