Torque brace?

I have seen what I think you are talking about.   I have this in a few brass steamers.   There is a brass strap that is screwed into the side of the gearbox near the top, out of the way of the mechanicals.   This is at the back end of the side toward the motor.   The other end of the strap is screwed to a bracket on the frame or directly to the frame.   

I have also done this on at least one loco I have remotored.   

Forgive my ignorance here, but is that basically a pair support struts that keep the gearbox from trying to rock forward or backward when the power is transferred to the axle?

I believe it's called a torque arm.  If needed they can be installed with a KTM or NWSL gearbox.  A lot of it depends on how you connect the motor's output shaft to the input shaft of the gearbox.  Some couplings do away with the need.  Many MG & USH (KTM) models had a support bracket that eliminated the need.

Too many variables to answer directly.

Jay

Here's a photo of one that I found on the web.  This is HO scale; I'm not sure if this is an NWSL gearbox.  I would personally be a bit leery about tapping and drilling the motor case!

From this photo it's apparent how the torque arm prevents the gearbox from rotating toward the motor, and relieves any thrust load on the motor bearings.  

I would love to see some photos of your typical installations in O-scale.  -Ted

A very sharp old Lobaugh engineer once told me about the lever principle - the longer the lever, the less force to hold a shaft in place.

I take the NWSL box, add a much longer worm shaft (they sell the proper drill rod, but I think it is 1/8") and couple it to the motor with a very short hunk of Toyota #0 hose.  The shaft needs a hunk of K&S tube soldered on, since the hose is looking for a 5/32" shaft.

Ted,

I believe the installer used one of the existing 2mm holes in the case.  Makes me wonder if they used silicon to mount the motor to the frame....a practice I loath.

I'll see what I can find for examples.

Jay

Here's an installation where the coupling eliminates the need for a torque arm.

This one kind of goes along with what Bob was describing except he uses the rubber tubing from Toyota (BTW, I do too sometimes).

This is a little different and more complex but it hides the drive line.

This one probably could have used a torque arm.  I believe I change the coupling later but forgot to take a photo.

This one has rubber tubing and the support bracket & bearing.

That's enough for now.  My back hurts from sitting here too long.

Jay

I notice some tubing type couplings which work well as universals.   I have found that model airplane fuel line tubing works for this also.   And it is naturally impervious to all lubricants I have found.

I too have used fuel tubing and it works fine for small, low powered locos such as HO, On3 and the very smallest O Scale but it will never work for larger and more powerful locos.  It just can't withstand the massive amounts of torque and HP required to move the larger stuff.

Here are some more examples of mechanical arrangements meant to stabilize the gearbox.  As you can see, there are a few examples with torque arms.  Most of these (not the diecast KTM) came from my junk box.  Most were replaced by said KTM or NWSL gearboxes.

Jay

This is all I have to offer.  It does not illustrate the point, but on the other hand it does illustrate my philosophy - hide the gearboxes and driveline, use minimum bearings (but always ball bearings on the worm shafts):