# Servicing 377/378 GP Diesel



## Nuttin But Flyer

My next project was to ascertain the problem with this particular tandem. The engine does not run, only hums and the lights work when power is applied. The reverse unit was also not functioning. I took everything out of the shell and examined the reverse unit. I found the lower set of fingers damaged -- one was bent around at an odd direction and cracked. I replaced it and reassembled the reverse unit in the engine chassis. Much to my amazement, the reverse unit now operates when power is applied and switches through its cycle each time it is turned off and on. However, the motor still does not operate. From initial examination, it appears quite dirty and in need of general cleaning. I have looked at the Greenberg manual and T.Barker's service instructions. Each shows an "E" ring at the top of the engine mount which can be removed to drop the engine out of the chassis frame. However, with the wires attached, they must pass through the hole where this unit was mounted and that seems awfully tight to do so unless they are unsoldered. Is there an easier or preferred way to disassemble the motor from the chassis to give it a good cleaning?


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## Gilbert Guy

I clean the 370 motors by carefully removing the brush springs and brushes. With the brushes removed I have a clear shot at the commutator. I clean out the commutator slots with a pin and rotate the commutator while cleaning with a tv tuner soaked q-tip. You can get at the commutator without taking off the brushes but it's easy to take them off and replace if needed.


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## Nuttin But Flyer

This can be done without removing the motor from the chassis?


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## Gilbert Guy

Yes. So far I haven't had a need to take the motor off of the chassis to clean the commutator, replace the brushes and get 61 year old motors running just fine.


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## Nuttin But Flyer

Thanks for the tip, I'll look into it tonight and let you know how I make out.


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## Nuttin But Flyer

OK, my first time trying to service my 377 isn't going as smooth as hoped. I've cleaned all the gunk from the motor armature, gears, etc. I sprayed contact cleaner all over the contacts, wiped everything clean. Scraped the gunk from between the grooves in the armature. Checked the brushes which are about the same size as new ones, the holders are intact, the springs are intact and "springy", all wires attached with good solder joints. I lubricated the armature with very minute amount of oil and greased the gears sparingly.The reverse unit operates as it should but the motor will not turn. When power first applied after re-assembly, the armature turned maybe a quarter turn then that was it. Reverse -- Forward -- Reverse, etc. No change. It will not move. I checked to be sure the armature is free by pushing it around with a screwdriver -- it seems to move quite freely. I did not change the adjusting screws that center the field. To service the engine, I removed the lower pivot screws on each side of the yoke that holds the motor assembly in place and serviced it, then replaced it back ino the yoke and re-installed the two pivot screws. Any thoughts? Did I miss something?


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## Gilbert Guy

Sounds like what I first experienced with the motors moving a quarter turn. Not having the means to test electrical draw, etc. I took the quarter turn as a positive step. If it moved a quarter turn it can move a complete turn. I then locked the reverse unit so as not to cycle then applied a continual off/on power pushing the engine a few inches trying to get it going. After many attempts over several days the motors began to turn beyond 1/4. It was as if the motors were frozen and the cleaning and continually applying on/off power while pushing finally broke them free. They have been very good runners ever since. Maybe I was lucky but that's what worked for me on two individual old GP7 motors. Beyond that you may have to get into the armature windings for breaks.


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## Nuttin But Flyer

The only thing I did not do was to change the brushes and holders. Unless I receive other thoughts here, I'll try that tonight.


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## Aflyer

In post #6 you mentioned that you did adjust the centering screws on the armature yoke. Could that be the problem? 
What about backing off each screw 1/4 turn and trying the motor? If that changes things you could then retighten them one at a time until you get a perfect centering job.
Good luck,
Aflyer


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## Nuttin But Flyer

Aflyer -- No it was not the centering screws that I removed. The screws I removed are item 28 in this screen shot of the service manual....

http://myflyertrains.org/gallery/album209/3745_2

When I finished with the cleaning, I simply re-installed the motor assembly between the yoke bracket legs and re-installed the screws.

Last night I removed the old brushes and tried to install new ones. However, not knowing how these are attached to the copper holders, I assumed they were soldered. I tried to solder them but it didn't seem to work too well. They are attached but the brush and holder assembly seems so fragile that I'm afraid the slightest bump will dislodge the brush from the holder. There is a small nub protruding from the end of the brush which appears to fit into the hole of the copper holder. Being sure I have the brush oriented on the proper side of the holder and also oriented so that the slight curvature of the brush matches the armature when installed, I attempted to solder the outer side to the copper holder. However the solder did not seem to flow too well to cover the nub and holder. Am I correct trying to do this or is there another method that I am unaware of? I lost two new brushes and copper holder strips last night -- the first was soldered with the curvature in the wrong orientation and the second one broke off after it was soldered when I slightly bumped it against one of my tools.


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## Gilbert Guy

From your description it appears that the brush holders and brushes for the 374 are similar to the 355 Baldwin with a single hole in the end of each brush holder and a nub at the end of each brush. I have replaced brushes in the 355 by simply positioning the brush nub in the brush holder hole with no solder. They hold up well in the 355 with just the brush spring tension.


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## Nuttin But Flyer

Really? That surprises me as the old ones I removed were soldered. But now that you mention it and I think about it, that makes a Hell of a lot more sense. Thanks for the tip. I'll try that. Hopefully, replacing the brushes is the issue to get this baby running again. If not, you'll hear from me -- actually if it does run, you'll hear from me too.


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## Gilbert Guy

Initially I thought the 355 brushes had a dot of solder on the brush holder but turned out to be just the brush nub. Don't know how a metal brush holder arm can be soldered to a carbon brush. The 377/378 were produced in 56/57, the same years as the 355. Those brush holders and brushes were different from the 1950 370 model which had a metal/brass small rectangular tube attached to the bottom of the brush arm and held a no nub rectangle type brush. If all else fails you could substitute those type of brush holders. In any case good luck.


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## Aflyer

Aflyer said:


> In post #6 you mentioned that you did adjust the centering screws on the armature yoke. Could that be the problem?
> What about backing off each screw 1/4 turn and trying the motor? If that changes things you could then retighten them one at a time until you get a perfect centering job.
> Good luck,
> Aflyer


What a difference a word makes, I apologize big time. My post was supposed to read;

In post #6 you mentioned that you did NOT adjust the centering screws on the armature yoke. Could that be the problem? 
What about backing off each screw 1/4 turn and trying the motor? If that changes things you could then retighten them one at a time until you get a perfect centering job.
Sorry again,
Aflyer


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## Nuttin But Flyer

I never touched the centering screws when I disassembled this beast, therefore I never thought they would need adjusting. However, since it did not run, perhaps that is an alternative to try. Unfortunately, I have moved backward with problems arisen by attempting to install new brushes. As the previous ones were soldered to the brush holders, I also tried to solder the new ones to new brush holders. This did not go well. As someone earlier stated, he did know how you can solder carbon brushes to copper or brass, whatever those holder strips are made from. And I can see his point as it was difficult to get the solder to flow over and onto the brush nubs once they were in place. When it seems they were soldered, a slight bump and they would break or fall off. His suggestion was to simply insert them into place at assembly and allow the tension of the spring to hold them against the armature. As crazy as that may sound, I think that is a valid suggestion. The nub should keep it in place with the spring tension on it. There is a posting earlier by Reckers when he rebuilt a GP7 -- check here........ 

http://www.modeltrainforum.com/showthread.php?t=4785

Looking at those pictures, the brushes are obviously soldered to the holders as well as the wires. His wires actually were threaded through the fiber board of the brush holder -- mine weren't. I also treid to dupllicate that set-up by threading my wires through the fiber board and soldering them to the holders at the brush nub location -- nah, that didn't work well. I would need a complicated fixture to hold all three pieces in place before applying the heat and solder. I think before I end up losing all my new brushes on mistakes, I'll simply solder the wire to the holder at some convenient point of its length and insert the brushes loose as suggested above and allow the spring tension to hold them. Then, once reassembled, adjust the centering screws if at first it doesn't run. In the meantime though, with all the re-work I have done, the wires are much too short to conveniently work on the unit. So I must lengthen them with added pieces of wire and shrink wrap or install completely new lengths of wire in place of the old ones. Either way, I have some work to do before re-attempting to install the brushes. The only good news to report is that I tested the resistance on both the armature and field, and both tested within range at 1.9-2.0 ohms. At least something positive was accomplished.


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## Gilbert Guy

I stand corrected regarding the brush attachment to the old 370. I just dropped down the front truck and as in the picture above the brushes are soldered to the brush holder. But the original brushes on the motor appear to have a very slight layer of metal/copper/brass on the top of the brush which would facilitate its soldering. I just installed new brushes on a 355 Baldwin and those replacements did not appear to have any metal top unless the nub itself is metal. I did not solder these brushes and the motor runs fine. Again, good luck.


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## Nuttin But Flyer

G Guy --

Looking at the remaining stash of new brushes in my possession, and I need to do so before I start trying to work on this or they will all be ruined, they do have a copper coloring on the surface that butts up to the brush holder. However, it does not appear to be any sort of metal, only colored as such. I am not aware if this is a coating to help the solder to adhere or if it is just a result of the manufacturing process. Despite this discovery, I will still install them loose when the time comes and see what happens. It will be a while before that happens as I plan to lengthen the wires in this engine to facilitate easier work on it. I got wire and shrink wrap tubing to do the job. Thanks for the update.


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## Reckers

Flyer,

On the basis of what you've posted so far, I'd start with replacing the brushes: it's one of those things that will prove worthwhile, even if it doesn't cure what ails your locomotive and helps to eliminate one major "how about..." Second, don't treat the field screws as sacrosanct. Whoever had the unit before you may have fooled with them before you had a shot at it and the field is now pulling the armature up into an inoperable position. Remember, these were made for kids to be able to tweak and repair by trial-and-error.

Third, get a schematic of the tandem and carefully study it for washers on the armature. Over the winter, I bought a non-working handcar. It was pretty filthy inside and someone had done some pretty sloppy soldering in an attempt to fix it. Once I cleaned it up and reassembled it, it still would not work. It would advance about a 1/4 turn and then lock up. It had a single, thin metal washer on one end of the armature. I talked to a LHS repair guy, an older (even older than me!) gent who I respect as all-knowing. My theory was that there should be a washer at each end: they kept it from rocking up at the free end and cramming the gears. He thought that was absurd, but grudgingly sold me a washer that should fit. The car now pounds it's way around the track: it's jerky, but those things have a rep for being jerky. The point was that a washer at each end trapped the armature in a horizontal position. If this is the issue, you would then be able to adjust the field frame to a no-contact position and everything would stay put. Even if there's no washer in the pic, it might be worth a try---there was no second washer in the LHS guy's pic, either.

Best wishes on it,


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## ChopperCharles

To start with, you can order brushes from portlines that come with the metal arm and the brush already attached. That's the way to do it. They're cheap too. Second, you REALLY need to remove the armature completely, chuck it in a drill, and spin it while holding a green scotchbright pad soaked in contact cleaner against the commentator. Do that, then put the armature back into the holder and torque everything down, being sure the bearings are centered in the cups inside the cast truck. GREASE the gears liberally while you're in there, and lightly oil the bearings. This with new brushes will likely fix your problem.

Next, completely disassemble the reverse unit, and clean the drum with a green scotchbrite pad and contact cleaner. It should SHINE. Replace ALL of the fingers - these are dirt cheap and easy to replace. Just because it cycles doesn't mean good electrical contact is being made.

If you do all of that and it still tries to turn but doesn't quite do it, the problem is the centering screws. It may turn freely by hand, but when the electromagnets engage it will pull the armature into the field coil and the armature will bind. 

Charles.


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## Reckers

Nicely said, Charles!


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## Nuttin But Flyer

It seems that all suggestions are pointing to the centering screws -- this is one item I did not touch, so it is entirely possible that after removing the armature, they will need some adjusting. How does one know which way to turn them in order to get a positive reaction from the motor? Is it trial and error only? However, before I attempt that, I am going to extend my wires to make working on this gal much easier. The motor wires are so short that the chassis is always in the way and I cannot get the motor into a reasonably good working position to remove or install the screws and other components. Once that is done, I'll install new brushes -- loose at first as suggested above -- then clean everything again. I'll also replace the top finger unit as I had only replaced the lower one. Then I'll let everyone know from there what result I have. Thank you all for your help.


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## Nuttin But Flyer

I have re-wired and installed new brushes. I re-assembled the motor with the field and the yoke that holds it in place. I did not return the motor assembly into the chassis yoke so that I would have access to the centering screws for adjustment. When power is applied, nothing happens. I have turned, loosened, turned again and loosened again each of the centeirng screws and the screws that hold the yoke over the field assembly. Nothing, not even a nudge. To be sure I have this wired correctly, I double-checked with the various wiring diagrams available online and in manuals. I specifically used the wiring diagram on Portlines' web site under his "AF Clinics". Everything appears correct. There is a rainbow set of wires from the reverse unit forward. Of these there is a red, green, yellow and black wire. Orienting the loco chassis with the motor yoke forward and the reverse unit toward the rear, I have the motor assembly oriented in the chassis with the commuter forward in the chassis with the field assembly oriented with the wire connections also forward -- the red wire nearest (or left side) and the black wire farthest (or right side). The brushes are wired with the yellow wire on the same side as the red field wire and the green wire is wired to the brush on the same side as the black field wire. If I am successful, here are photos showing how everythig is oriented and wired.......hopefully, someone can chime in with suggestions or an obvious mistake that I made. Thanks.


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## ChopperCharles

Does it get hot? If you supply power and the assembly heats up but doesn't turn, power is flowing through correctly, but it cannot move because it is binding.

By the looks of your photos, your field coil is not properly seated. It should not be at an angle like it is, the sides should be parallel to the bracket that holds it in place. There are indentions in the motor chassis where it should fit nicely. At an angle like it is, I'm absolutely sure it's causing binding. It doesn't take much.

Charles.


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## Nuttin But Flyer

I have not noticed any heating, but I noticed the field at an angle too. Yet despite my attempts, it seemed to be fully seated in the motor chassis. Because of the angle, I was thinking that I might be installing it backwards from the way it should be inserted. However, you didn't say anything that leads me to believe it is reversed so I will assume I have it in the correct orientation. I'll take it apart again tonight and see if I can re-seat the field in the motor housing so that it is straight. Thanks.


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## tjcruiser

Flyer,

I'm a Lionel guy, not an AF guy, so take all this with a grain of salt ...

Whenever I'm trying to revive and/or debug an old motor, the first thing I do is remove the e-unit from the equation ... fully disconnect any wires that would normally run from there to the brushes, field coil, etc.

Then, I use some simple aligator clip jumper leads to power the motor as follows:

Power via jumper into one brush can; jumper from other brush can to a field coil terminal; jumper from other field coil termimal back to transformer.

Sometimes, depending on the motor itself, one of the "points" above is grounded to the motor frame, in which case that should be your circuit endpoint, so to speak.

Notwithstanding the more experienced AF comments above, but have you tried to run the motor with jumpers and the e-unit removed, per the above?

Separately -- are you sure that by not installing things (motor, eunit) back in their frames, you haven't omitted a needed ground circuit connection? (I ask this naively ... A Lionel e-unit needs to be mounted in the motor frame to complete its ground circuit, for example.

TJ


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## Nuttin But Flyer

I accept assistance from anyone, so don't needlessly categorize yourself as a "Lionel only guy". An electric motor works by the same principles whether it be in a Lionel or American Flyer or an HO scale engine. I serviced the reverse unit first when I started this project, replacing the fingers and cleaning the drum and other parts. I have not tried to isolate the reverse unit from the motor, but was considering doing so if the suggestion from Charles of re-fitting the field coil didn't work. The only reason I have not done so to this point was that I did have power to the motor before attempting to replace the brushes. The motor turned slightly just before disassembly for cleaning. With that, I am assuming the reverse unit and wiring to be intact and working. This is my first real attempt at my own repairing/servicing of AF engines, so there will be some learning as well as mistakes made.


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## ChopperCharles

Depending on where you connect the power, it may very well be that the motor must be attached to the bracket in order to operate. Keep that in mind as you are testing.

If you end up completely stuck, send me the chassis I'll get it working for you. Just cover shipping!

Charles.


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## Nuttin But Flyer

Thanks for the tip. However, I want to exhaust all my opportunities so as to learn how to do this myself. I have several other engines that will need servicing too, and don't want to have to rely on others to do it when they require it, but I do appreciate your offer. Let me fumble through this for a while and let's see where it leads.


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## Aflyer

Nuttin But Flyer,
The saga continues. Two things I didn't see mentioned in yor newest posts; first does the armature seem to turn easily by hand, as in the whole centering and alignment discussion. And secondly how are you applying power to test the motor?

Aflyer


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## Nuttin But Flyer

For everyone who offered assistance, she is up and running now!! Thank you all. I think it was Charles' post that mentioned the motor assembly probably needs to be installed in the chassis yoke in order to be "grounded". I did re-install/reseat the field in the motor body and reset the field yoke as well as the centering screws since he noticed it slightly angled in my photos. But it seemed after installing the motor assembly in the chassis yoke it suddenly began to work -- just as Charles suggested. Now before I replace the chassis into the shell, I still have one issue -- I installed the brushes loose as per someone's suggestion above. It does work, but will they stay in place?? I noticed that they are not perfectly straight in a vertical alignment. They seem to lean slightly toward the motor armature winding but maintain contact on the commuter. It hasn't seemed to make any difference running it forward and reverse several times for several minutes at a time. Any thoughts? I had first tried to solder the brushes to the brush holders when I began this project a couple of weeks ago and it did not go well -- the solder seems to fail to flow properly and the brushes seem to just melt or disintegrate. Oh, and those pesky centering screws??? I just tightened them against the field once it started to run. If there is an adjustment to be made that will increase performance, I sure don't see how it can be done when the screws are inaccessible once the motor is installed in the chassis yoke.


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## tjcruiser

Nuttin But Flyer said:


> I think it was Charles' post that mentioned the motor assembly probably needs to be installed in the chassis yoke in order to be "grounded".


... uhh ... Ahem ...



tjcruiser said:


> Separately -- are you sure that by not installing things (motor, eunit) back in their frames, you haven't omitted a needed ground circuit connection? (I ask this naively ... A Lionel e-unit needs to be mounted in the motor frame to complete its ground circuit, for example.
> 
> TJ


:thumbsup:


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## ChopperCharles

oh TJ, don't be hatin' You may have said it first, but I used such eloquence that he was bedazzled by my post. 

Charles.

(hehe)


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## tjcruiser

Me thinks your typewritten letters are much more handsome than mine!


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## Nuttin But Flyer

OK, guys. There is no need for competition. Everyone who offered sugestions here were all helpful. I appreciate everyone's input. I have like 10 other engines to work on. There will be many more opportunities to compete with each other later on.


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## Nuttin But Flyer

I am still baffled over how to adjust the centering screws. Apparently you have to remove the engine assembly from the chassis yoke, tighten or loosen a screw, then re-assemble to try it. Seems to be really difficult to get it precise. How would I know if the field is centered properly to obtain the best performance?


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## Nuttin But Flyer

There I go again, not thinking outside the box. All I need is a jumper from the chassis to the motor to ground it and then I should be able to adjust the screws while testing the motor for performance. Sometimes I amaze myself.....but this wasn't one of those times.


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## tjcruiser

Nuttin But Flyer said:


> Sometimes I amaze myself.....but this wasn't one of those times.


:laugh:

Been there, done that (the "wasn't" part) ... many, many times on my end!


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## Aflyer

Nuttin But Flyer,
Hi, just read your new thread, and wondered if you had received desired results with this one? Are you now getting good results with this Diesel?

Thanks,
George


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## Nuttin But Flyer

I have not run it on a track yet, but she runs good on the bench both forward and reverse. As I am still learning how to service my own engines, time will only tell how well I have performed. As I tackle the others, I'll post my progress. Thanks for the interest.


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## Reckers

Flyer, thanks for taking the time for all those posts and sharing the details: it's going to help a lot of people in the future.:thumbsup::thumbsup::thumbsup:

The same goes for everyone who contributed---it's like having a gang of experienced rebuilders gather around the table and offer suggestions until the job is done. The next guy who has this problem and comes to the site is going to find a wealth of information, good suggestions and support. It's people like you that keep this hobby going and make S scale viable: thank you all.


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## T-Man

*This is a shame with no pictures.*


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## T-Man

I wanted you to see this. A movie of the diesel sound in action. This sits in the 378.


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