Question on Lionel MPC 634 Santa Fe NW-2

Thanks for the response. Perhaps both fields are energized. How can I determine? The wiring of the unit appears to conform to the Greenberg schematic on page 62 of the 7th edition, however.

swede

If this uses a old style alco truck that is swedged together.  The plates may have shifted...causing the armature to bind in one direction. 

Do you mean it growls and won't move?
If so, you are probably missing an insulating washer that goes on the screw that holds the solder tab to the top of the brush plate.
This is a very common problem on postwar and modern era diesels with 2 position reversing (manual or e-unit)

Here is a page from the Lionel Modern era service manual. The solder lug and screw is circled. Note that the insulating washer is not shown. Some motors were assembled with a plastic screw, eliminating the need for the insulating washers. I am not certain which locomotives had those plastic screws, might be very late postwar.

Thank you all for the responses. This unit was not running at all when I got it. Now, the light is lit in the forward and reverse positions, it runs fine in forward but "growls" with no movement in reverse. The unit is wired as Ubermeister indicated with no wires touching except the twisted red and green wires connected to one brush. The brushes were cleaned up, are still of good length, smooth and even. The armature is not bound and the insulating washer for the solder lug screw is present. What I did observe this AM after reading your responses is that the armature rises a good 1/16th inch when the wheels are manually turned in reverse and it takes more effort to manually turn the wheels in that direction as opposed to the forward direction. There is no set screw to limit the armature travel. Is there supposed to be a bearing in the armature cover to limit travel? 

Thank you, swede

Some Lionel diesel motors have washers on top of the commutator to limit upward motion of the armature assembly. I am not certain whether the 634 had them. If not, you can add them.

Does your 634 have one driven axle, or two?
How about traction tires?

If you have one, it's time to get out your VOM meter.
check the leads to the terminals on the side of the reversing unit.
Cycle the e-unit by hand.
Only one terminal should be connected to ground at a time.
The ground should alternate back and forth.

You could have a bad insulating washer, or something else causing a ground condition.

Worse case, one of the field windings could be bad. If that is the case, you could always install a 3 position e-unit and use the good coil.
The coils don't go bad that often. When the field coils are a problem, its usually because one of the leads is broken off and the end cannot be retrieved.

Am responding to only one of your latest posts right now C.W.B. Will get to the second one after morning chores are finished and I have time for trains. The 634 has two driven axles with the gearside wheels grooved for tires (none there right now).

Thank you, swede

C.W.B. Am confused (easy to do) with your most recent post. This unit has no "E" unit at all. Just as with the guy posting in 2012, all that exists is a lever sticking up through the chassis slot, that is manually positioned between two contacts, for either forward or reverse. Is there supposed to be a complete 2 position "E" unit? I know the Greenberg book shows one on page 62, for the 633, but it does not look like there ever was one for this unit. Would a photo help?

swede

Postwar Lionel 634 locomotives have an e-unit.
When they first started up, MPC put together some switchers using 634 cabs. These engines have the switch you describe.
If you have an MPC 634, it should have a radio wheel, a bell and marker lights on the locomotive.
It should also have an early MPC diesel switcher motor truck with pickups, and an early MPC diesel switcher dummy truck without pickups.

Pictures would be helpful.

Use your VOM meter to make certain that only one contact at that switch is grounded at a time.

It does sound like he has an early 8010 with a leftover 634 cab. The giveaway is the manual reverse and two axle drive.

LOL, Swede identified his loco as being an MPC 634 in the title. I guess it didn't register in my mind.

Thanks for the responses, C.W.B. and Rob. The cab has the bell, marker lights and radio wheel as you describe, C.W. and the imprint on the bottom cover of the truck/motor assembly reads 8010-127. It looks like www.lionelsupport.com/media/su...nt1to9/1Complete.pdf , supplement 1, page 375 of 501, except my motor has no thrust bearing screw. 

C.W.B., I checked for continuity between each position and ground and regardless of the switch position, left, center (switch not connected to either post), or right, I read continuity between each post and ground.  

Let me know what pictures you would like and I will post them.

Thanks again, swede 

C.W.B., I checked for continuity between each position and ground and regardless of the switch position, left, center (switch not connected to either post), or right, I read continuity between each post and ground.  

If you are getting a zero ohms reading (dead short to ground) then that's a problem.  Try removing the screw holding the solder tab. make certain it isn't touching any metal, and either take another set of readings, or just try the loco.
Are the wires touching anywhere?
Are the switch contacts touching metal anywhere?

Sorry for the delay responding. After reading C.W.B's last post, I disconnected every wire and found no shorts or opens. I then powered the motor without going through the switch. One lead to one brush, one lead to the single red field wire, applied power and touched the twisted red and green field wires to the second brush. The motor ran fine. It also ran fine when I applied power to the second brush and touched the twisted pair to the first brush (reversed). I had the same results placing a power lead on the green field wire. Thinking everything should be fine, I hardwired the motor following the Greenberg schematic for the 633 on page 62, but ignored the part dealing with the two position "E" unit. Operating results were the same as when I first posted. The unit ran fine in forward but would not reverse. Do I need to wire it differently than shown in the Greenberg book?

Thanks again, swede 

Try it this way:

Thank you, Rob. That was it. Where did you come up with the schematic? I very much appreciate the assistance from all.

Thanks again, swede

I just redrew the one from Greenberg without the reverse unit.

Your problem, as I suspected(which caused me to redraw the diagram), was that insulation issue at the solder tab and screw that CW correctly identified as the most common problem with these motors. That's the only electrical change I made. It's an easy issue to miss/overlook, even when it's described in writing in detail. It was the easiest way to get you to take that connection off of the solder tab without telling you why you were doing it.

Rob, I did disconnect the solder tab following CW's instruction and the motor ran on one direction as it should. The two wires to the solder tab were not soldered together and I did not think to simply connect them before testing the motor. If I had, the problem would have been corrected. As it was, I was so happy to get the motor running after using your schematic that I did not notice till just now what you had me do.

Thanks again, swede

That insulated solder tab provides an important mechanical function... it provides a strain relief / anchor point for the field wire, and that's it.

If it shorts to the motor chassis/ground, you will have the operational issues you experienced.

That insulated solder tab provides an important mechanical function... it provides a strain relief / anchor point for the field wire, and that's it.

I only recommended removing the screw from the solder tab as a diagnostic step. I should have been clearer about that.

C.W.B. As I was working to get the motor running, I never gave a thought about the function of the solder tab, Maybe if I had looked at the Greenberg wiring diagram more closely I would have realized the solder tab did nothing except to provide an anchor point. I completely glossed over the fact that the connection purposely went nowhere. 

My thanks, swede