# Locomotive only pulls in one direction



## ChopperCharles

I have a GP7 diesel, and I took it apart and cleaned the armature. Chucked it in a drill and spun it, then used scotchbrite and electronics cleaner to make the commentator shine. 

The locomotive still only pulls well in one direction. In the other it goes roughly the same speed, but has no pulling power whatsoever. I tried pulling a train of 6 cars and it could manage it at 30% throttle in one direction, and at 100% throttle in the other direction it was just creeping along, and then started smoking a little bit.

I've had it apart, I don't see anything wrong, the wiring is in good shape and it's obviously getting power. Why is it doing this? Bad armature? Bad brushes?

Charles.


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## Stillakid

*Runs slowly....*

Charles, from Tom Barkers CD, 

Runs Slowly/High Current-Elliptical hole worn into drive wheel bushings(the bushings should be circular with very little play)

Runs Slowly In One Direction, And Slowly Or Not At All In Other Direction-Field not centered

Motor Starts Only With A Push-Armature wiring shorted or open

Not having one of the diesels, other than this from his repair manual, can't help you out.

Good Luck!


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## T-Man

You also have a worn armature bushing to check too.


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## gunrunnerjohn

Another thing not mentioned is wear on the gear train. I had a couple of older dual-motored diesel units that would run better in one direction than the other. Turned out that subtle wear in the gear train was the issue. I swapped gears and motors around until I got a combination that worked well in both directions.

I think the issue is that the locomotive runs most of it's life in one direction, so eventually the gears will take a set.


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## ChopperCharles

Well.... my locomotive will sometimes only start with a little push too (in the bad direction), so that's telling me armature. I checked the field coil and it's centered. The brushes are also throwing off a LOT of sparks, which I understand if another symptom of a bad armature. I will try swapping with another diesel I have. Not sure if the 360 armature will fit, but it looks like it should. If that works, I know I have a bad armature. 

Charles.


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## gunrunnerjohn

Hard to imagine a bad armature would only affect one direction, it'll be interesting to see what you find.


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## ChopperCharles

I don't know either. it's really weird. It seems also if it's in the forward (bad) direction, I can flip it on the left side and the motor speeds up, flip it on the right side, and the motor slows down. I can also stop the wheels at full throttle with my hand quite easily in forward, but that takes serious force in reverse.

Charles.


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## gunrunnerjohn

Bottom line, this could still be a gear thing, but if it's dependent on the armature commutator facing up or down, I'd be looking closely at the motor brushes and commutator plate. 

One thing you can do here. Monitor the current drawn in forward and reverse free-running. If the weak direction is drawing as much or more current, I'd suspect some gear train binding. Does it turn freely in both directions?


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## tjcruiser

Just checking in here ...

I think you guys are on the right track with suspecting mechanical issues (gear, axle bearings, etc.), rather than electrical issues.

I don't know much about AF S diesels, but I'm wondering if that loco has a worm gear setup??? If so, torque in a forward direction vs. torque in a reverse direction can shift the armature axially between bearings to the point where there's substantially more friction in one direction.

Is it a worm gear setup? Is there much axial "play" in the armature shaft (or the worm gear drive shaft)?

(Sorry for not being more specific ... not that knowledgable with S / AF motors.)

TJ


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## ChopperCharles

I don't think it's a gear issue, everything moves nicely. There's maybe 1 thousanth of movement front-to-back when changing directions. Not much at all really. I've had this motor apart completely, cleaned, lubed, and reassembled. It worked the same before I farked with it, no change after the servicing.

Charles.


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## NIMT

Have you tried a different Transformer to power it?


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## ChopperCharles

Yeah, I have two test transformers and my main one. Just disassembled the reverse unit and put it back together sparkling clean, that's not the problem. Going to swap in an armature from a different loco now and see if that fixes it.

I kinda am leaning towards sending it to portlines and having a can motor and dallee installed... but I'd like to keep it original if possible.

Charles.


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## ChopperCharles

Well, looks like you guys were right after all. I swapped in armatures from a different locomotive, and the performance was all around crappy - both directions. So I looked a little closer and found that with the new armature in there, I could press on one of the brushes and make it go faster. Disassembled the entire thing again, and on closer inspection, the brushes were worn funny, and they had a glaze on them. Cleaned them up with a file and put the original armature back in, and it runs much better now. Going to spring for new brushes next time I make a portlines order.

Charles.


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## tjcruiser

< Sniff ... sniff ... >

I just love happy endings!


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## T-Man

You may need new springs too.


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## lilb

The problem might be with the bearings. Over time they wear into an egg shape and the alignment gets way out. You can see if they are worn by moving the wheels up and down and left to right, if there is excessive play you may need to replace the bearings. If it is one of the early diesels, the bearings are removable and are easy to replace and you can most likely do it yourself. You can buy them from Portlines. If it is one of the later diesels they just milled a hole straight through the chassis and you will need to send it somewhere to get holes for new bearings drilled. It has been said that the electrical current that the wheels are picking up is arching through the bearings and causing them to wear prematurely. I need to replace the bearings on some of my engines and on one I am going to insulate all the wheels and make pickups out of phosphorous bronze and see if this fixes the wear problem. And if it is the bearings, it is not good to run the engine anymore until you get them fixed, as it can damage other components too.

Brian


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