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motor bearing problem

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I bought my ADC shunt motor used on ebay. I put the car together and got it running. The motor made a sound like a loud wheel bearing which, since I'm not that familiar with large electric motors, I didn't know if it was normal or not.

I had the bearing replaced and it sounded much better, much quieter.

Now, about 3 months later, the motor is making the same loud bearing noise that it did before.

My questions are:

Could I have received a bad bearing?

Could the shaft be bent and put undue stress on the bearing causing it to be louder?

Could the bearing be improperly seated in the front motor mounting plate?

Could the motor and trans be out of alignment to such an extent that the bearing is overstressed?

Could there be some other reason or cause for this bad bearing noise?

I am using a Lovejoy spider coupling with a plastic insert that should compensate for a small misalignment.

To fix the problem, I've got to take most of the system apart. I would like to replace the bearing but I'm afraid that the new bearing will also fail.

Thanks for your ideas.

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774 Posts
If the motor sounds good when you bench test it and the shaft is running true then the problem is in the way the motor is connected to the transmission. The adaptor plate looks questionable to me. It does not look strong enough and may be flexing. The love joy type coupler is not going to last no matter how well aligned the motor and trans are. The back and forth torque will tear the rubber spider out in no time.
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