8753 MPC GG1 "Lazy" Pullmor

[RAVL]

Now that our two sons are of the age to enjoy and run trains, we recently built a new layout and have been taking trains out of storage.  One of my old locomotives, the 8753 GG1, has an issue where one of the motors is what I can only describe as "lazy" and doesn't run at the same speed as the other.  If it relevant, we modified this GG1 when I was a kid because it is of the type that had the holes in the bottom of the power trucks and my mom would get very annoyed at Christmas with it dropping grease on the carpet.  So my father had it converted to the postwar style power trucks, and he had the armatures ground down as the originals were too long (I believe this is why MPC punched those holes in the bottom of the trucks, IIRC).  The work was done professionally and the locomotive ran fine afterwards for years and was then put in storage.

I have been through the locomotive thoroughly:  the armature face has been cleaned, new brushes, old grease cleaned out of the trucks and worm drive and everything freshly greased, etc.  The truck wheels do not seem to bind as well.  Yet the problem persists, although it runs fine in one direction. If run with the lazy motor in front, it will struggle a bit and eventually start to slow down and heat up.  Obviously I stop it to prevent this from continuing.

I am kind of out of ideas here.  Anyone have any thoughts?  Thanks in advance.

[TrainLarry]

Were the motors completely disassembled, cleaned and lubed? If so, make sure all wiring is good and solid, especially the wiring between motors. Resolder all connections if in doubt. Insure the brushplate is clean, and the brush springs have sufficient pressure on the brushes. Pull the motors out of the trucks and run them free of any load and compare performance. If one motor is still slower, swap the armature and brushes from the bad motor to the good one and see if the problem remains with the motor, or was switched to the other motor. Report back your results.

Larry

[sir james I]

You did everything right.

But did you replace the brush springs as well?

[RAVL]

Thanks.  I will go back and double check my work.  I will also test the motors off the trucks to see how they respond.  

[cwburfle]

Check your power trucks.
The worm on the end of the armature shaft tends to push the gear to one side or the other, depending on which direction the train is running. Sometimes the slight shift creates binding.
It could be the worm gear itself rubbing against the truck block, or the backs of the wheels rubbing against the magnets or truck blocks.
This usually only happens in one direction, and is not at all unusual in worm drive powered units.

[RAVL]

CW,

I notice that when I rotate the wheels manually, they are smooth but the gears on one power truck do shift slightly towards the outside of the truck when moved in (what I believe) is the problematic direction.  If this turns out to be the issue, what fixes are there, if any?  I don't have the ability to pull wheels or similar.  Thank you again for your assistance.

[cwburfle]

Try rotating the wheels manually while pushing them to the side. Do you feel a bind?

To address a bind without removing the wheels:

Get a couple of 671M-23 or 671M-19 motor shim washers.
Cut a slot into the washer so it looks like the letter "C".
The opening in the "C" should be just a bit smaller than the diameter of the axle.
Snap the washer over the axle, between the wheel and the truck block.

[RAVL]

Excellent -- I will try this as I've checked all the normal culprits already.  Do you have any preferred way to cut the washer cleanly?  Thank you again for the help.

[cwburfle]

I've used the washer trick, but I do not remember how I cut the washer. Either filament snips or maybe a cut off wheel. Whatever you use, make certain the washer Is clean and smooth, with no burrs.
You don't want it grinding things away in there.

Normally, I would disassemble the truck. I have the tools to do it.

[cwburfle]

One more thought: Before you put in the washer, make certain it is not going to cause binding.
I don't think you will be able to remove it without taking off a wheel.

[RAVL]

Thank you again.  Much appreciated.

[servoguy]

If the motor turns OK in one direction, but not the other direction, the problem is usually end play in the armature.  When the motor turns one direction, the armature will move up.  The other direction will have the armature moving down.  If one of the directions causes the armature to bind against the brush plate, the motor will not run well in that direction.  Check the shims (washers) that set the end play for the armature and make sure the armature is not rubbing anything.