Kadee Coupler Tips

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The subject of this page is application of the Large Scale Kadee knuckle coupler. I don't intend to spend much time comparing the Kadee coupler against other brands. If you'd like this information, check out the August 1996 Garden Railways for an article entitled "Comparing Couplers" or see the original version of the article at Large Scale Coupler Tips.

As you might have noticed from another tips page on this site, The Care and Feeding of LGB Knuckle Couplers, I also use LGB Knuckles but on a different layout.

Sometime after 1990 while I was developing the Geologically Improbable Railroad, Mountain Division I investigated the Kadee coupler but rejected it for a couple of reasons. It was (and still is) hard to manually uncouple and spotting cars downgrade from an uncoupling magnet is impossible. Also at that time, the price of the LGB knuckle and the Kadee coupler was equivalent. Even though its appearance was less than ideal, I chose the LGB knuckle because it worked really well in that application.

When I started the outdoor version of the Geologically Improbable Railroad I reevaluated my choice. This time I chose Kadee couplers for several reasons.

Since most of my proposed rolling stock would be Aristo and would have Aristo couplers already installed, I had considered using the Aristo knuckle for awhile, but I decided against it.

I ended up with Kadee couplers on the outdoor layout. However, once that choice was made, more decisions were required. The implications of those decisions is the real subject of this page.

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What is a Kadee Coupler?

The Large Scale Kadee knuckle coupler is a scaled up version of the HO coupler which has become a defacto standard in the HO world. It works pretty much the same. Operation of the Kadee coupler is described in Kadee's Web Site at How Our Couplers Work.

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Which One?

photo of #1 and G side by sideLarge Scale Kadee couplers come in two sizes, G scale and #1 scale. These are approximately the right size for 1:22.5 and 1:32 scale stock. The table below contrasts the advantages and disadvantages of each size.

The G Scale couplers use 3 digit numbers such as #831. The #1 scale couplers have all the same mounting configurations and have a four digit identifier such as #1831. This convention doesn't hold true in all cases. The popular #830 in G scale has an equivalent in #1 scale, but it is the #820.

"G" Vs. #1 Scale Couplers

"G" "#1"
Appearance Too big Good

Better than #1 Scale

Stays coupled in more situations

More difficult to uncouple a single car

Uncouples more easily on abrupt vertical gradients

Car Spacing Somewhat larger than #1 Scale Less than "G" Scale
Compatibility with other brands

Couples to LGB, Aristo, USA, Lionel

Poor with Bachmann

Less reliable than "G"

Doesn't work with Bachmann at all

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Coupler Mounting

photo of closely spaced body mounted carsOnce you've picked a size, you must decide how you want to mount the couplers. If you want to get car spacing like in the photo, then body mounting is the ONLY way to go. However, if you haven't designed your track geometry to take body mounted couplers into account or you don't understand the geometry issues, then you should use truck mounting. You can mix and match, truck mounted and body mounted couplers will interoperate.

If you are planning a layout and would like to use body mounted couplers, then I recommend that you get the book "Track Planning for Realistic Operation" by John Armstrong. Actually, I would recommend that you get this book and read it cover to cover anyway. You'll learn a lot from a man who knows his stuff. This book discusses track geometry issues in depth and all of the information presented there is applicable to large scale trains. Pay careful attention to the track geometry issues or you will have troubles with body mounted couplers. Body mounts will have more difficulty coupling on curves than truck mounts under any circumstances.

photo of usa boxcars mounted at an acceptable spacingIt is possible to achieve acceptable car to car spacing with truck mounted couplers as shown in the photo of these two USA Trains cars. To achieve this spacing, modification to the tang on the truck is necessary. If you just attach an #831 to an LGB or similar car, you will have to drill a new hole for the screw and the coupler will stick WAY out. Then the cars will be spaced very far apart. You can close this gap by almost 1-1/2" by cutting off the end of the tang on the truck and using the original screw hole. If you are afraid that this modification is too severe, don't worry about it too much. The old coupler will still screw back on and be fully secure. The extra part of the tang really isn't necessary. You will end up with car to car spacing that is 1/2" to 1" larger than body mounting (depending on the car design) but the spacing is at least getting reasonable.

photo of closely spaced aristo hoppersCouplers on Aristo cars can be truck mounted and produce a little closer spacing than other cars, see, Truck Mounting on Aristo Cars. Again, the spacing is determined to some extent by the design of the car.

Comparison of Body Vs. Truck Coupler Mounting

Body Mounting Truck Mounting
Mounting Difficulty Requires car body and truck modifications Can be mounted on most cars without modifications to the cars or couplers
Car to car spacing Can be set to prototypical distance

Tends to be much wider than prototypical spacing

Closer car spacing can be accommodated with minor modifications to the coupler mounting tang or the coupler body

Curve Tolerance Requires larger radius curves (4')
Intolerant of "S" curves

Handles 2' radius curves well

"S" curves are OK

Tolerance to being pushed Handles pushing well

Higher drag due to truck cocking

More prone to derail, especially on turnouts

Drag in curves Lower, trucks are free to follow the track with minimum drag Higher, coupler forces twist trucks and causes flanges to bear on rails in curves
Coupling on curves Can be unreliable even on 4-6' radius curves. couplers tend to flop sideways instead of mating even when mounted on short stock such as the ore cars shown above. Longer stock will behave worse. Couplers face each other more directly and will usually couple on 4' radius curves without regard to the length of the rolling stock. Coupling on 2' radius curves is also possible if you shim your wheelsets to keep the coupler centered
Train Length Longer train lengths possible as the buffing forces are transferred directly through the carbody and don't impact the interaction of the truck and the track. Train lengths are limited by the forces on the couplers, especially in curves. Figure on 12 to 15 cars maximum for reliable operation.

kadee height gaugeNo matter what kind of coupler mounting you select, you should buy a coupler height gauge. The device comes in two versions, #829 for #1 scale and #880 for G scale. This device makes it very easy to determine if you mounted the coupler at the proper height and it checks out the operation of the coupler. It also has a track and wheelset gauge indicator cast into its base. A jig that is attached to the bottom of the gauge can be used to properly center and set the height of an uncoupling magnet.

The Kadee coupler is very sensitive to proper mounting height. If the coupler body is too low or too high, they are more susceptible to coming uncoupled. This is especially true of the #1 scale couplers. If the trip pin is too high, the couplers will not reliably uncouple at an uncoupling magnet. If the pins are too low, they'll catch on the magnets and either kick the top part of the magnet off or derail the car. They can also catch in frogs or other track elements.

Not only is it important that the coupler height be correct without external loads, you also have to pay attention to the coupler height under the dynamic loads placed on them while in a train. If the coupler mount is not stable, the couplers (especially truck mounted ones) will tend to dip when they are loaded. This will cause the trip pins to catch on magnets or other track elements such as turnouts when the car is part of a train, but not when the car is tested by itself. The fix for this is usually to tighten the truck mounting screw. If the tightened screw restricts the ability of a truck to rock side to side a little, this can also cause derailments. You want a truck to rock side to side and still not allow the coupler tang to rock up and down. It may be necessary to devise stops to prevent the trucks from rocking fore to aft.

Truck mounting on LGB and USA Trains cars is straightforward, just cut off the extension of the coupler tang and mount the coupler using the existing hardware in the existing hole. The tang is stiff enough such that the #831 will naturally come out at the right height.

Bachmann uses a much softer plastic for the truck so that the tang can deflect. It may have taken a "set" in a deflected state. If the coupler doesn't come out at the right height, warm the plastic tang with a hair dryer and then deflect the tang back in the correct direction as the plastic cools. You may have to fudge it several times to get it right.

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Coupler Configurations

Kadee makes a large variety of mounting configurations, most of them are special designs for a particular piece of rolling stock or locomotive where the mounting is a little odd. For most cars, you can get away with just a few types.

You can see all of Kadee's configurations at G Scale Couplers or at #1 Scale Couplers.

Some Kadee coupler styles, such as the #830, have a draft spring that both centers coupler and provides some give in the draft gear. I personally don't like this draft gear arrangement as there is a lot of runout in the couplers as you literally stretch out a train. This makes it more difficult to control the train and can be really frustrating when you are trying to uncouple cars near the end of a train. I prefer the stiffer mount of the short box type such as the #835. However, the lateral play capability of the short draft box couplers is more limited that that of the #830 configuration. On longer cars, the #830 tends to deal with track geometry issues better than the short draft gear box version. However, on many shorter cars, the larger draft gear box of the #830 won't fit without sticking out too far.

Kadee #830 Kadee #835
830 #835

Truck Mounting on Aristo Cars

coupler box modified to mount on aristo trucksKadee #831 coupler boxes can be easily modified to mount on Aristo cars in such a way that the car to car spacing is at least close to prototypical. The only way to get the cars closer is to body mount the couplers.

I use a Dremel cutter tool to grind off the back part of the coupler box so that it will tuck under the axle. Then the coupler can be mounted in the existing hole. If you've used metal wheels with a smaller diameter than the stock Aristo plastic wheels, you may need to use one of the black Kadee supplied shims under the back part of the coupler body to cant the coupler upward to the right height.

There are some other issues related to truck mounted Kadee couplers on Aristo cars, see Aristo Car Tips for more info.

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Coupler Performance Issues

The Kadee coupler has a good reputation for performance, although it does have some idiosyncrasies. The major one stems from the Delayed Coupling feature that is used for spotting cars away from a magnet. If your engines do not run smoothly at low speed or your track isn't dead level while you are spotting cars, you will become extremely frustrated. In the delayed coupling mode, the cars will be inhibited from recoupling for only as long as the couplers remain in physical contact. If any slack develops, the couplers will snap back to their normal coupling mode and recouple the next time that they touch.

Kadee Coupler Performance

Pro Con
Coupling Easy anywhere as the couplers never latch shut Easy anywhere, even if you don't want them to
Manual Uncoupling No advantage Difficult, can be aided by a special tool
Automatic Uncoupling Easy, fairly reliable

Requires track magnet

Couplers must be mounted at the correct height

Must have good slow speed engine control

Magnets on mainline may cause undesired uncoupling

Magnets get in the way of track cleaning

Magnets will trip sound systems

Car Spotting Delayed uncoupling allows car spotting away from a track magnet

Can't spot cars downgrade from a magnet

Unsteady locomotive motion will upset delayed uncoupling

Weather Resistance Poor Springs and trip pins rust
Coupler Mounting Height Can be set with a coupler height gauge Proper mounting height is critical for reliable uncoupling

If you elect to paint your couplers and still want them to work properly, the mating surfaces of the couplers MUST be free of All vestiges of paint. Even a wisp of paint on the front of the knuckle will cause the couplers to cease to couple properly. Clean any paint off the mating parts of the couplers with a cotton swap soaked on lacquer thinner and then rub graphite onto those surfaces.

If couplers that used to uncouple and couple properly start misbehaving, then you will probably need to lubricate them with graphite. Retreatment with graphite is needed every few years. Observe where a pair of couplers touch each other and liberally coat those surfaces with locksmith graphite. Squirt a little on a scrap of paper towel and use the towel to rub the graphite on all the mating surfaces. If the coupler does not swing side to side freely, then squirt some graphite inside the coupler box and work the coupler side to side to distribute the graphite.

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Automatic Uncoupling

The Kadee uncoupler is a strong magnet mounted between the rails. The mounting heights of both the couplers and the magnet is critical to achieving good reliability. Kadee makes several versions. Two are already integrated into track sections, one is designed to be permanently mounted in an existing track section and one is "portable." I use only the portable version as I want to be able to move the uncouplers around as my operational plans mature.

kadee portable uncoupler The Kadee #844 Portable Uncoupler is a four piece assembly that mounts on and between the ties of LGB or Aristo European style track. When this device is called portable, you have to realize that for it to work, it has to be glued down so that portability is somewhat limited. The magnet is strong enough to lift itself out of place in the presence of the coupler trip pins. While I am still trying to determine optimal locations, I use a little ordinary contact cement to hold it down so that it won't jump all over the place. After a "final" location is determined, I use Crafter's GOOP to stick it down more or less permanently. You have to be sure that the layer of glue is very thin, or you will have troubles with trip pins striking the magnet.

If you use track with different tie spacing, such as Aristo American style track, then you will need to trim off some of the material from the bottom magnetic piece so that it will fit around the tie plates. The magnet material is very soft so that it can be trimmed easily with a rail nipper or wire cutter.

kadee 842 uncouplerThe #842 magnet is somewhat less expensive than the #844, but you have to cut away some ties to make it fit and I find that it provides little operational advantage over the #844 except that it does seem to work better on some cars. There is a little more mass of magnet and pole piece in the #842 so it MIGHT have a slightly stronger magnetic field. However, when new, the #844 works quite well.

To install the #842 on Aristo US style tie strips, I use an end mill bit in a Dremel tool and grind through the tops of two ties just barely through the top of the tie. Then the magnet will go on at the right height using the Kadee test gauge as a placement tool. Some form of filling or expanding adhesive should be used like Gorilla Glue, Liquid Nails or Lexel.

After 12 years, I found that the automatic uncoupling function of all of my #844 magnets became less reliable. Often, the couplers just would not spring apart in some places and on some cars. I dug out a spare magnet that had been in storage all that time and it worked better, especially on the more obstinate cars.

I figured that the magnets may have become weaker with age so I bought some new ones. I find that the new magnets work better than the older ones. Then I devised a simple test. By removing the whole magnet assembly from the track and holding it upright, I tried to lift a screwdriver from my workbench by the tip. After finding the right weight screwdriver, I was able to determine that the strength of the new magnets was indeed stronger than the older ones, with the one that was in storage being midway in strength. Apparently, these things have limited lifetime and need to be replaced eventually.

The mass of the total magnet does indeed have an impact, the top part by itself is quite a bit weaker than both parts together. Further, the presence of the steel pole pieces has a significant impact. Adding two extra pole pieces also makes any given magnet stronger. Even the old and rusted pole pieces improve the performance of the magnet when used in addition to the new pole pieces. Perhaps the extra magnetic material and larger pole piece of the #842 can provide an advantage.

Since I now know exactly where I need uncoupler magnets, I'll start installing #842's in those places and still use the #844's for temporary positions.

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Manual Uncoupling

Manual uncoupling is one of the most frustrating limitations of the Kadee coupler, especially if you have fat fingers like mine. Don't even try with your fingers. Just pick the car up so the couplers pop over each other.

You can use a tool to aid in manual uncoupling and then it becomes fairly easy. Just grab one of those real long 3/16" straight blade screwdrivers that comes with almost every screwdriver set. Its the one that you've never used. From above, place the blade in the gap between the couplers and twist 90 degrees and the cars will just pop apart. I've also used a chop stick with a flat whittled into the end.

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Example Kadee Coupler Conversions

I have converted quite a bit of equipment to Kadee G scale couplers. I have used some of Kadee's conversion kits, then I figured out that I could adapt only a few types to work on everything. Finally, I ended up adapting the Kadee #831 for everything, but sometimes with a zero or medium offset coupler in place of the large offset version that comes in the #831 kit.

Example Kadee Conversions
Loco or Car Coupler Type Link
Aristo Pacific 831 New Aristo Pacific Tips
Aristo RDC 831 RDC Tips
Aristo SD45 831 SD45 Tips
Aristo Doodlebug 831 Doodlebug Tips
Aristo Center Cab 831 Center Cab Tips
Aristo RS3 831 RS3 Tips
Aristo 0-4-0 831 0-4-0 Tips
Aristo FA1 793 and 831 FA1 Tips
Aristo C-16 831 C-16 Tips
Bachmann Shay 831 or 821 Bachmann Shay Tips
LGB 22232 (0-4-0)
similar to 2-4-0
831 LGB 22232 Tips
LGB 2060 (industrial diesel) 831 LGB 2060 Tips
Lionel Atlantic 831 and 794 Lionel Atlantic Tips
Lionel Thomas 831 Thomas and James Tips
USAT GP7/9 831 USAT GP7/9 Tips
Aristo Snow Plow 831 Aristo Snow Plow Tips
Aristo Freight Cars 831 Aristo Rolling Stock Tips
Aristo Heavyweight Passenger Cars 831 Aristo Heavyweight Tips
Aristo Streamliner Passenger Cars 831 Aristo Streamliner Tips
USAT Trains Caboose 831 USA Caboose Tips

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© 1997-2009 George Schreyer
Created Oct 25, 1997
Last Updated September 27, 2009