Yes, and no, ...mostly maybe...

Dear Joe,

Mechanically the differing size heads do couple together, and Kadee promote both as being backwards/forwards compatible. However, some modellers have reported issues with the auto-coupling and delayed-uncoupling, due to the differing "gathering ranges" of the differing sized heads.

If you are a hands-on skewer-uncoupling kinda guy, you should be fine. If however you rely on magnet-uncoupling and push-together coupling-on-corners operation on your layout, then such mix-n-match situations may cause frustration down the track (esp over time as the mechanical tuning of the couplers may not be maintained adequately...)

Happy Modelling,
Aim to Improve,
Prof Klyzlr

No Issues Here

I have a mixture of Kadee types and experience no problems with the "scale" head and other sizes coupling and uncoupling reliably.  I use skewers for uncoupling, so can't opine on magnetic uncoupling performance.

Mixing KD5 and Scale Couplers

I say don't do it.  I have seen no end of trouble on several layouts.  Yet I hear of others, like Rob, who say it works fine.  I can tell you this -- the Midsouth Model RR Club in Baton Rouge tried to switch over, and they found that the scale couplers gave problems even when mating with each other, and even worse when mating to KD5's.  Ultimately, they pulled all the scale couplers and went back to KD5's.

It's a personal choice.

#5's, #158s, #119s oh my...

Joe, 

I mix and match without any issues that I've noted. 

It may depend

upon a grade you have to traverse, or rather how sudden of a rise.  I had a rather abrupt angle 'going up' when I had some different sizes and things drifted apart.  A slow speed up that area revealed the smaller head lost grip, literally coming up and off the other. It was a Kadee PS-1 boxcar with scale, smaller head couplers and a larger Kadee #5 (I think). A slight adjustment to my riser under that area of track fixed it, but beware.  I needed a more graceful and gradual transition form one grade to another, and it actually looks and runs all cars better, so it was a hidden blessing.

Mixing sizes

I do what the OP has planned: scale heads on locomotives and cabooses, no. 5s on most cars.  Works fine for me. 

I do find it is very helpful to have a Kadee gauge set up with a No 58 installed, and make sure the mounted scale coupler lines up exactly with the gauge.  The smaller head leaves no room for error. 

On the equipment I primarily use on my table at home with 18" radius turns, I generally stick with no 5s on everything.  The greater gathering range helps out on the tight turns.  The table is flat, so no issues with vertical separations. 

Mixing sizes

I've been putting KD scale couplers on most new things but there are lots of old things with standard #5s.  I've never had a problem.  The only new thing that gets #5s are rotary dump coal cars.

Paul

A mix

Problem here

For the most part I don't have a problem once they are coupled together, and I have no problems uncoupling using either a skewer of Rix uncoupler. I have no ramps so I can't comment here. I do have problems coupling up though, even on straight level track. I have to occasionally use the skewer to open the jaws of the scale coupler, or make two or three attempts. My experiences only.

willie

Mixed Kadee's

Joe, it depends on the use, for instance if a loco is always used in the lead position a scale coupler on the front is great for photos. Also on both ends of a caboose, they look great. At our local club (Napa CA) we follow  Joe F's and SP tradition of really long trains with multiple power lashups. Not only are our pulling couplers #5's but they must be metal, the plastic ones just don't hold up to club use. John Colley, ex Port Townsend, WA but now in Sonoma, CA

What works for me

I have been moving to Kadee's "scale" couplers for several years now.  I find that as long as they are mounted at the property height, 158's ad 5's work well together.

My favorite coupler is the true scale couplers from Sergent Engineering.  I have insalled them on most of my locomotives.  They are compatible with Kadee "scale" couplers, but not with standard head No. 5's

They work together, sometimes

MIxed Kadee's

I don't have a problem with mixing because I don't do it.  I run on a club layout as well where the trackwork is not what I could or would call above average, in fact the old layout is something like 20 years old and the trackwork is quite frankly bad.   The new layout is being constructed at the moment and is to the point of being able to be run on with helix, dips and rises and crossovers and assorted complicated trackwork.   I have run 50 car trains on both and have had no issues at all and I use the Kadee 158 and short shank versions of the same scale head whisker couplers exclusively.

The trick with them that I have found is that they have to be mounted at a perfect height level to work efficiently there can not even be a minor deviation in height levels from the gauge.   I am pedantic about it in any case as it is one of the things that can make running a nightmare, the other two being wheels out of gauge and  lightly weighted cars mixed with heavier ones.

I use them on locos and passenger cars as well and have had no trouble there either.

Just my 2c worth.

Rob McLear

Australia.