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I have an MTH premier passenger train that I installed kadees on.

On an upward grade, two of the seven cars almost always become uncoupled.  

It appears as the grade starts up, the rear coach coupler on the lead coach lowers enough just to loose contact with the car behind it.

Bad trackwork?  Bad kadee install?  A little bit of both?

Thanks for your thoughts.



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I'd check the "vertical curve" at the bottom of the grade. If it's too sharp, the end of the car is going to dip pretty far. Also watch the vertical curve at the top of the grade as well. Unfortunately, some of the things we get away with using hi-rail couplers can come back to bite us when we switch to Kadees (I know this from a lot of personal experience).

Last edited by AGHRMatt

Bad is too strong a word.    As matt says above could be either.   

When you install Kadees, check them on a flat straight to see if they are all at the same height.     Compare car to car, or use a Kadee gauge.

Bumps and humps in the track can cause this or too quick a transition into a grade.   

The length of the cars also contributes to how this stuff affects them.

When I started running 2-rail equipment at the club (MTH scale-wheeled locomotives and various rolling stock), I quickly found out where our track work had become compromised from years of thermal expansion/contraction and coastal moisture tweaking our benchwork. While it didn't have an impact on hi-rail equipment, my six-axle diesels would find them and we'd fix the problems. Made things better all around, but we're looking at a major reworking of a large curve by the farm on both mainlines because the 20-plus years have taken their toll on the Gargraves flex (we're looking at replacing it with Atlas O-99 and O-108 fixed curves). The benchwork decks are all 1/2" plywood so our vertical curves are well eased and our grades are 1.5% on the mains and 2% on the branch.

Scale City Designs  (  makes and sells shims that are exactly the same size as the Kadee box in 4-5 different thicknesses, thickest being 1/16 inch.

You should settle on a coupler heigtht, and then insure that all cars couplers on both ends  are that height.    The simplest thing to do is buy a Kadee coupler gauge and use it to set all cars at that height.    If  you choose some other height, you should make  your own gauge to be able to consistently check and measure if couplers are mounted at a correct height.

I think you have been advised to check for dips and bumps and too quick transition from level to grade or grade to level.

With Kadees, I am going to guess the coupler head is about 3/16 inch high.    I think 3 rail couplers are 1/2 inch in height.    So with a kadee if there is a track condition that causes one car to rise or drop 3/16 inch vs another, they will uncouple.

You can get away with some differences in mounting height, but not nearly as much as with 3 rail couplers.

The long shank 74X Kadees can be a bit of a challenge. The shims have to be straight and level lengthwise as the extended length shank makes a nice teeter totter on uneven track. I also tend to spend a bit of extra time eyeballing the knuckle height against 805s like your pic. If you don’t use the actual 740 knuckle as the height reference you’ll get a pesky height delta like you’re seeing. 

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