Pecos River Brass 4-6-2

[mmagliaro]

You're missing something.  The metal drawbar is attached to the tender, and even if everything is painted, sooner or later it will be intermittently touching the tender and the underside of the engine.  Any time it makes electrical contact with the underside of the engine and the tender at the same time, it will short.
You could put a plastic washer between the drawbar and the underside of the engine, and then put a nylon screw and nut in there
to hold it.  That should be safe.   You could do that at the tender end also.  As long as one end is completely connected by nothing by plastic, it should be okay. 

[peteski]

. . .  Since I'm removing the engine motor lead from the whole drawbar/mounting screw piece, couldn't I just leave the old drawbar attached, still use it for a connection to the loco, and not even worry about it electrically?  . . .  My concern is the drawbar/screw/spring connection and ridiculously tiny clearance between all of that and the frame under the cab (less than 1mm).  If the drawbar is making momentary contact with the frame (even a painted part), that theoretically shouldn't be an issue since the current from the motor wire no longer goes through the drawbar, correct?  Or am I missing something?

Yes,  you are missing an important fact.  It has nothing to do with the "current from the motor".  In the brass locos the entire (metal) loco is electrically connected (through the loco wheels) to the right rails, while the entire (metal) tender is connected through its wheels to the left rail.  So the entire tender is always opposite polarity than the loco. Any time any part of the metal  tender touches the metal loco, there will be a short. They are both electrically live at opposite polarities.

The motor just taps into the circuit by connecting one of its terminal to any metal part in the loco, while its other terminal has to be routed to the tender, connecting to any part of the metal tender.  That is why that drawbar post on the loco has to be insulated from the locos frame (or any other metal part of f the loco.  Your while problem seems to be around that post, and a plastic drawbar will be a kind of a workaround to keep the tender from contacting the loco.

That is why it is important to keep those 2 separate and isolated from each other.  That is where the plastic drawbar comes in.

[ATSF_Ron]

Thenks Peteski.  That helps me visualize things better.

[ATSF_Ron]

This has been a super frustrating experience.  I fabricated a new drawbar and lengthened the motor wire.  I left off the front and rear trucks of the loco to eliminate any other possibility of shorts.  In the cradle it still runs like a fine watch.  I put it on the tracks, clipped the new motor lead directly to the tender and it ran!  For about two inches.  Then it stopped.  I can tap it and it'll run for about another 2 inches before it stops.  It's still shorting somewhere and I'm seeing red over this thing.  I suppose it might be possible that the painted brass brake rigging is shorting, but it doesn't look like it.  I'd rather not butcher an expensive brass loco by clipping them off unless I know for sure that's what it is.

What else can I check, guys?  I'm ready to give up on this thing.  Between this one and my SP C9 I'm ready to wash my hands of brass N scale for good!  The brass steamers I had in the 80s/90s never ran this poorly and were super reliable.  Maybe it's bad aging on these locos?  I dunno.

[ATSF_Ron]

These pics show the new extended motor lead with heat shrink tubing.  It tucks up into the frame when fully assembled.  I'll probably need to use some tacky cement or something like that to hold it in place so it doesn't interfere with the trailing truck.  IF the *&$# thing will ever run right!

[mmagliaro]

This has been a super frustrating experience.  I fabricated a new drawbar and lengthened the motor wire.  I left off the front and rear trucks of the loco to eliminate any other possibility of shorts.  In the cradle it still runs like a fine watch.  I put it on the tracks, clipped the new motor lead directly to the tender and it ran!  For about two inches.  Then it stopped.  I can tap it and it'll run for about another 2 inches before it stops.  It's still shorting somewhere and I'm seeing red over this thing.  I suppose it might be possible that the painted brass brake rigging is shorting, but it doesn't look like it.  I'd rather not butcher an expensive brass loco by clipping them off unless I know for sure that's what it is.

What else can I check, guys?  I'm ready to give up on this thing.  Between this one and my SP C9 I'm ready to wash my hands of brass N scale for good!  The brass steamers I had in the 80s/90s never ran this poorly and were super reliable.  Maybe it's bad aging on these locos?  I dunno.

I don't know what miracle brass you were running in the 1980s.  As a general rule, N Scale brass is really poor, running-wise except for a few lucky exceptions, mostly from Samhongsa, and that Santa Fe 4-6-2, which is usually a smooth cherry of an engine.
It does look like the brake shoes could be touching the drivers.  You should not have to remove them.  Just gently pry or sand the inside faces with a strip of sandpaper between the wheel and the shoe, until you open up some clearance.   Anything that can touch
the left-side drivers: the rods, valve gear, brake shoes, will cause this.  Absolutely nothing from the left-hand drivers can touch
anything metal on the frame.
As for that wire, I know you are frustrated with this engine, but that wire will probably have to go.  It is far too thick and will interfere with the tracking of the engine, especially on curves.  It needs to be very thin stranded wire.

[mmagliaro]

Here's a photo of a Pecos River 4-6-4 (very similar mechanism).  The backs of the left-side drivers kept touching the frame, shorting it out.
So I had to file away a little metal on the frame where the rims ride.

[ATSF_Ron]

I had a similar C9 from Key, a C8 from Oriental, I believe, a Key AC12 (Japan version), and a couple of MT4s.  All were exceptional runners with decent slow speed capability.  Not Kato mikado or Bachmann connie smooth, but good enough for me and quite good for the time.  Maybe I just got lucky.  I acquired the newer C9 and the PRB loco very recently.  Quite uncommon running quality, for me anyway.  I think I have a handle on the C9, once I get the proper hex wrench to deal with the traction tires.  But this PRB?  I may be in over my head in terms of ability/willingness to grind on it and keep tweaking.  I was also wondering the same thing about that wire.  I thought I got a small enough gauge.  Supposedly this stuff is 22 gauge.  Looks like it'll have to be 24 at least.

I'm willing to try and sand down those brake shoes and replace the wire again, but if that doesn't do it I'm most likely going to unload it to someone who is more of a tinkerer.  This has not been my idea of a good time.  Thanks again for the tips, Max.

[ATSF_Ron]

Max, here's a thought I had while considering options.  Instead of grinding in that small space by the drivers, do you think small shims of super thin styrene glued in those spaces might suffice?  Or maybe some of that liquid electrical tape Micro Mark sells?  The thought of filing or grinding in that area of a brass loco gives me the willies!

[nkalanaga]

For a quick test, common clear plastic tape would work.  It probably wouldn't wear long, but would show if that was the problem.

[mmagliaro]

Yes, the tape idea would be good for testing to see if that is where your short is coming from.

If the drivers prove to be the problem (by testing with the tape), some .005" styrene (which you can get in Evergreen sheets)
would work, but not forever.  Styrene is pretty soft and eventually, it will wear through.  A better choice might be some Kapton tape.
You can get a roll of 1 mil (.001") thick, cut some small pieces and put them on with a contact cement like Walthers Goo.
I wouldn't count on the tape adhesive by itself.  Kapton is really tough and durable, as well as slippery.

[ATSF_Ron]

Ahh, good ideas with the tape, guys.  I need to hit my LHS today, so hopefully they have some.

[Simon D.]

One thing. On my Pecos Brass pacific it’s very easy to put the front truck on the wrong way up. Causes a massive short.

[ATSF_Ron]

Thanks Simon.  I had both front and rear truck off and it was still shorting

[ATSF_Ron]

I'll try some other kinds of tape I have lying around.  The LHS had the Kapton, but I'm not buying a $22 roll of tape when I need less than a couple of inches.