couplers

[Guilford Guy]

Kadee #148 or #5. 148 is a number 5, but the centering spring is wires on the couplers themselves, as opposing to a separate piece of copper.

[Running Bear]

I would like to replace a Kadee compatible E-Z Mate coupler on my Spectrum EMD SD-45, but I don't know what the size number is.
  HO Scale Model Railroading suggests using a hobby knife stuck between coils to insert the coupler spring.  I can't see if I have it in correctly; I can see that the coupler is not closing properly with the spring in it.

When an EZ-Mate has had it, that's it. Toss it. Kadee is the best way to go. The size you're looking for is #5 or the #148 whisker coupler as Alex suggested. I prefer the #5 myself.

[SteamGene]

I have never known a Kadee spring to hold more than a second if it's not in correctly.  However, the ends of the springs must be inside the two small posts at the top and bottom.  A thin knife blade does a great job.  With the thread trick, I use a threaded needle to get the thread through the spring.  Since learning that trick I have not lost a single spring.
Gene

[WGL]

 Thanks Guilford Guy, KCS 1, & SteamGene.  I'll look for Kadee 5#s.

[WGL]

 modeltrainstuff.com has just gotten back in stock McHenry 52 couplers that will replace the horn & hook couplers on my IHC passenger cars!  So far, my passenger train is running well with the horn & hook couplers wired together, so the MHC52s should be even better.

[Running Bear]

The McHenry is a Kadee wannabe and will not hold up well. It's all plastic and will twist under load. The Kadee is all metal and will stand up to loads that the McHenry can only dream of handling.

[WGL]

  The horn & hook couplers that came on my IHC passenger cars are all plastic.  They won't stay connected to each other, which is why I want knuckle couplers.  I haven't seen a Kadee metal coupler that is identical in design to the McHenry 52, & I suppose I couldn't just pop a metal coupler into the truck where I popped out the plastic one.

[rogertra]

  The horn & hook couplers that came on my IHC passenger cars are all plastic.  They won't stay connected to each other, which is why I want knuckle couplers.  I haven't seen a Kadee metal coupler that is identical in design to the McHenry 52, & I suppose I couldn't just pop a metal coupler into the truck where I popped out the plastic one.

Body mount all your couplers.  You'll find the cars will operate better.

[Running Bear]

I suppose I couldn't just pop a metal coupler into the truck where I popped out the plastic one.

You might want to try this one. It's made for truck mounting.
http://www.kadee.com/htmbord/page51.htm

[SteamGene]

Roger is right.  Cut off the Talgo arm or replace the truck and body mount the couplers with shim if necessary and coupler pockets supplied by Kadee. 
Gene

[WGL]

KCS1,
Thanks for the link.
  Will mounting couplers to the bodies of my 11" passenger cars still enable them to negotiate 18"r or at least 22"r curves, as they do now?

[Guilford Guy]

If you body mount(less derailments, operates better) use a "Long Shank" coupler. If you use a standard coupler, and it doesn't extend far enough, the diaphragms will collide, and being solid plastic, will derail the cars. http://www.kadee.com/htmbord/page156c.htm

[Running Bear]

If they have a lot of end throw, probably not.

[Santa Fe buff]

If I may toss in:

It also MAY depend on car model. Some passenger cars have longer 'over hang' then others. Therefore, need longer couplers. For me though, some times it's not the extension length... For I have a short coupler on a cylindrical hopper and it can go 18 radii without contact, but for it being hidden in there, it's simply a complete nightmare to even attempt to couple up. The point is, longer coupler shank, equals more distances between car and car, which that equals the cars being able to navigate sharper turns.

[Guilford Guy]

IHC cars have plastic diaphragms. When Coupled too close, teh diaphragms will collide and throw the cars off the track on a curve. If you body mount the couplers, with a long shank, such that the couplers extend beyond the diaphragm, they will be able to navigate the turns. However, I must caution you about coupling these cars to a short locomotive.

Red represents the car, and green represents the locomotive. Note how on the second drawing, the couplers cannot meet. If they had been coupled when going around a curve one would have been forced off the rails.