Model Train Couplers and Uncouplers

Train coupler

Uncoupling train couplers

Okay…so your train has left the freight yard, you’ve traveled over 100 compressed miles, and now here you are ready to deliver a carload of upholstery to a furniture factory. You’re backing into the spur and your “crew” is getting ready to uncouple the freight car so it can be left at the warehouse and unloaded. What happens next?...

Worst case scenario

Two giant hands come down from the sky and try to jiggle the freight car loose from the rest of the train. It doesn’t come loose right away so the hands have to lift the car off the track in order to unhook it, then try to rerail it again next to the furniture factory.

Next to the worst case scenario

One giant hand holding a big stick comes down from the sky and puts the stick down between the cars, between the train couplers; the big stick turns a little and the car rolls free.

Best case scenario

There are no hands in the sky. The train backs up into the spur and stops for a moment. The couplers separate. The train pulls forward a little, then backs up slowly, pushing the car into position next to the unloading dock. The train pulls forward with the spotted car remaining in place at the loading dock. The train then pulls out onto the mainline to travel to its next destination.

Doesn’t that sound better?

But, before getting into the details of uncoupling, let’s learn a little more about train couplers…

Horn hook couplers

These are the ones that probably came with your original equipment. They don’t look anything like the prototype train couplers. They rely on side pressure to hold them together. This is a major problem when backing up, because the side pressure often causes derailment.

Rapido couplers are used with most original N scale equipment with similar disadvantages.

Knuckle couplers

These are more prototypical, they look better, and they work well with the magnetic uncouplers. Also, you don’t have as many derailments when the trains are backing up. Kadee makes most of these for HO, Hon3 and larger scales, but other manufacturers like Atlas, Kato and Athearn are making them as well. Micro-Trains Line (MTL) and McHenry make knuckle couplers for smaller scales. The HO version is reasonably priced at Amazon...HO Scale Knuckle Spring Short Shank Coupler (2pr)

Some people like to put Z scale knuckle couplers on the fronts of N scale locos (or N scale couplers on the fronts of HO locos) because the smaller train couplers look more realistic on the larger models. The same idea can apply to the backs of cabooses (cabeese?).


Most people don’t like horn hook couplers and can’t wait to replace them with (or “convert” them to) knuckle couplers that are more realistic and work well with the magnetic uncouplers. This takes a certain amount of time and effort to convert all of your equipment to knuckle couplers, which is why people usually do this in a stepwise fashion, converting locomotives and cars one at a time, sometimes mixing them in consists till they are all converted. You can have several conversion cars on which you have a horn hook or Rapido (in N scale) coupler on one end and a knuckle coupler on the other so that you can connect both types within your consist. I like to do the rear of one loco and the front of the lead car first, so that it becomes easy to uncouple the loco from the rest of the train.

For N scale, the couplers are usually mounted in the trucks, and are rather difficult to replace without learning new expletives in your vocabulary. It’s easier just to replace the whole truck assembly (made by MTL).

Coupler height

No matter what kind of train couplers you have, they won’t work well if they are mounted at the wrong height. You will need a coupler height gauge for your scale to tell whether your couplers are the right height or not. You can get one from the NMRA or from Kadee, or even (HO only)...HO Coupler Height Gauge

Assuming the couplers are mounted on the cars, if the coupler is sitting too high, you can lower it by putting a shim between the bottom of the car floor and the coupler pocket. If the coupler is too low, you can add one or more washers between the truck and the car bottom. If the coupler is mounted on the truck, you may have to replace the truck assembly or the wheels, particularly if the coupler is too low.

Magnetic uncouplers

Kadee was the first manufacturer to develop this system, in which a special magnet (not just any magnet) is positioned under the track at a strategic location like in front of a branch line, spur or ladder, such that, when a train is backed up and stopped with the knuckle coupler over the magnet, the “glad-hands” of the coupler come apart when slack is allowed. The train should then be pulled forward a little, and then backed up again to push the car into the proper position without recoupling. The train can then pull out of the spur leaving the car where it was placed. This is called the “delayed uncoupler”, as opposed to the “regular uncoupler” which will recouple itself to the train after it is pushed back off the magnet.

Electric uncouplers

These are also available from Kadee for all scales, which are primarily electromagnets activated by applying current to a wire wrapped around a cylinder many times which creates a magnetic field. These have to be mounted in a space cut out from under the track, which is really no problem if you’ve used foam for your subroadbed.

Uncoupler installation tips

If you are going to use uncoupling devices, it makes sense to include them in your original track planning. It’s easier to install them as you are laying your track initially rather than trying to do it later, although it can still be done. You may have to use a rotary tool or track saw to cut out and replace small sections of track in order to place the magnets, but it wouldn’t be that difficult. If your track is already laid and you want to install uncouplers, go for it. You’ll be glad you did.

The website is an excellent reference on learning how these devices operate and the different kinds of uncouplers that are available. Another good reference especially for N scale couplers is at

Q&A on Train Couplers and Uncouplers
Q - I decided to use the delayed action, under the ties, magne-electric uncoupler, Kadee #309: I saw in the instructions that a momentary switch is needed to activate / deactivate. Can you please recommend a specific brand/model to buy?

A - Radio Shack Catalog #: 275-618 should work fine.

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