Fix That Short – Race Car World, Jul/Aug ’78 issue.

This information comes from an article published in the July / August 1978 issue of Race Car World. It should be used for research and entertainment only!


JoMac has received a few repairs where the consumer took the time to send his whole car back to us and complains of speed control using up power,” or “batteries that go dead after only a short time,” or “a speed control that doesn’t make the motor go fast anymore,” or “a loss of motor torque.” All these problems are generally a shorted motor. The easiest way to tell this is if the speed control heat sink gets too hot to touch-the motor’s gone. What causes the motors to go bad generally is a loose wound motor and the flexing of the armature wire due to RPM, vibration and pulsing of the controller whether an electronic or resistor kind.

When the armature flexes sometimes the insulation chips off the armature wire causing a short. This can happen anywhere in the stock causing from a 1 to 20 amp short. The best cure for this is an epoxied armature, but that is illegal by ROAR Class D Stock rules.

We at JoMac have never seen a worn out or burned out motor. All motors eventually short out in the manner described.

If this happens to you, and you are economically minded and not planning on running that motor in stock class, you can take your motor apart, unwrap the wire and relacquer the wire. Then once dry, rewind and assemble the motor.

(Race Car WORLD editorial note: Keep those old shorted motors. Soon a manufacturer may offer a rewind service for stock and modified motors. We’ll keep you informed as this is firmed up. There will also be feature detailed articles in Race Car WORLD showing how to prevent and fix shorted motors plus how to rewind and modify motors for Class D Modified races.)

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