Kadee 745 undesired uncoupling.

Yeah, the centering springs may be too stiff. I presume the glad hands are clearing the rails on that switch? And the couplers move freely in their pockets? No flash on the critical coupling surfaces?

The glad hands have been cut off, Ace. 

Yep.  They move too freely. 

Have you had problems yourself with the springs being too strong?

I was just trying to extrapolate my troubleshooting experiences with HO and N-scale Kadee couplers. I don't use Kadee couplers for O-gauge.

If the shanks are especially short that might be an issue, especially when running cars of different lengths into curves. But your illustrated case is a miniscule curve.

If your wheels have some drag it maintains tension on the coupler to help keep them coupled, especially when pulling single cars. But of course that's a trade off, since free-rolling wheels are desirable.

Maybe some careful work with a needle file in the right places would help, but that shouldn't normally be necessary. Is the trouble just with this pair of cars, or with others also?

Are you using the Kadee coupler height gauge?  Must admit that I have NEVER experienced such an issue with Kadee #805 nor the newer #740 series.

I have had the problem a couple of times due to the coupler not swiveling in the box. Last time that happened, I had over-tightened the plastic Kadee box and it was pinching the coupler shaft. Sometimes a little graphite sprayed into the box remedies that. Without a close-up video of the offending coupler, it's hard to tell what's happening.

Thanks for your replies, guys.

Matt's explanation was close.  I was actually not tightening the screws enough, allowing the draft box to swing.  

It wasn't very much, but it was enough.

OK on the straight, but it looks like it was affecting a few of them on the curves.

Maybe I'll put a bit of CA on the backs once I get them lined up.

At least it's an easy fix. 

I appreciate your input.

MaxSouthOz posted:

Thanks for your replies, guys.

Matt's explanation was close.  I was actually not tightening the screws enough, allowing the draft box to swing.  

It wasn't very much, but it was enough.

OK on the straight, but it looks like it was affecting a few of them on the curves.

Maybe I'll put a bit of CA on the backs once I get them lined up.

At least it's an easy fix. 

I appreciate your input.

 

Glad you're getting close to a solution. I like the 745's for brass cars as the box insulates the couplers from the car frame and prevents the risk of cars shorting through the coupler connection. But the boxes definitely flex when tightened too much and stick the coupler really well.

Why not use 2 screws, so they can't swivel?    If you tighten too much with plastic boxes, they compress and do not allow any coupler play.

Thanks.  That's been suggested by Sam from Kadee, as well.