Armature Testing?

I’ve had some issues with my 2001 GEM lately (D&D 7.5HP motor) where the car is running very rough, particularly during acceleration. Instead of a smooth acceleration the motor seems to suddenly slow (almost stop) then suddenly pick up speed again. Makes for a very jerky acceleration. I thought the issue might be with the accelerator pedal, but after replacing the pedal I still have the same problem. I took the motor off and cleaned up all the brushes and contacts. Measured resistance between the commutator contacts on the armature and the readings don’t seem to be very stable. Wondering if my armature is bad. Anyone know where in or around San Diego I could run a growler test on the armature? Would like to completely rule out a motor issue before mucking around with the controller.

Also, I hear rattling within the armature. I presume this is some of the original wire varnish that has chipped off and come loose. Could this be another sign that the motor has over heated and something is wrong?

I have a growler that I could let you use, but it takes certain skills and experience to to get good results.
I’ve forgotten everything I knew.

That is awesome, thanks! Let me know how best to connect.

<insert NEMA classified & “UL rated” joke here>

Random rattling might be foreign debris. I’ve seen the balancing lump of epoxy come loose and hop around in there. If it gets wedged in into the wrong two points it can take out a winding or damage a brush carrier.

A Consistent ticking might be something coming loose on the armature and catching a brush as it passes.

Does this noise happen when you run it in place? It might help with tracking it down.

Was there an event that might have set this off? Are you fond of high speed downhill runs? If you have bypassed the speed limiter then you need to watch your RPMs.

A deeper noise might be coming from your gearbox. A bearing going out is bad and will waste a set of gears real quick.

Post a shore vid of this noise if you can.

I’ve got the motor taken apart. If I shake the armature I can hear something rattling around inside. Wasn’t able to hear it at all when driving. We do have the speed limited to 35 MPH instead of the factory 25 mph. There wasn’t any single event that seemed to cause the problem. I’ve probably noticed for a year or two that the acceleration just kept getting less and less smooth until now it’s so rough that the car doesn’t feel safe to drive.

Is there continuity between any of the comms and the shaft? That would be bad.

Are there any open comms?

I haven’t been able to detect any obviious shorts with my hand held multimeter. The only thing that measured a little strange was the resistance between contact points on the communicator sometimes didn’t ever stabilize, but not sure this isn’t just an artifact of my multimeter.

or could be a broken, but semi connected, wire…

Fluke meters are notorious for this. They can be sensitive enough to read continuity across the user’s skin even they are only holding the insulated grips of the leads.