Question about Sears Craftsman LiftMaster Chamberlain Garage Door Opener Wireless Keypad Model 976LM Security+

2 Answers

Craftsman 1/2 hp 139.53648

Changed large gear without disturbing any other settings. now the motor only runs about 2 or 3 seconds and stops . nothing is jammed up as i dropped motor into my hands and tried it . still stops running after about 2 seconds , any suggestions?

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  • blueslover12 Jul 26, 2009

    thanks but i never touched the worm gear. thats whats puzzling me. I'll take a look though. any other suggestions?

  • blueslover12 Jul 28, 2009

    thanks to all for the help . the rpm sensor was bad .

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I agree with all the above. Your problem is with the rpm sensor 'little board'. Check to see that there isn't pieces of the shredded gear blocking the two black squares. Blow on them or whatever and make sure they are facing each other. Also make sure the sensor is plugged in. In almost all cases when replacing the gear you HAVE TO unplug the rpm sensor and sometimes if you haven't done it before the plug 'looks' like its plugged in. Unplug it and plug it in to verify.
The only other thing I have seen in older openers is that the spacers will wear out on the motor shaft and the black cap will go outside the rpm sensor area. With the cover off run the opener and watch the shaft where the black round cap is. If it moves more than one quarter an inch (or out of the rpm sensor area) then you need to replace the spacers that are worn out and gone. If you purchased a gear kit normally it comes with the spacers etc.

Posted on Jul 28, 2009

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Make sure you put the black cup bank on the end of the motor shaft and that it is pressed all the way on. Make sure the rpm sensor is plugged in. If neither of these is the issue then you probably did not have the motor shaft pushed all the way back when you tightened the coupler after replacing the worm gear. Loosen that coupler and from the front of the motor (opposite end in which the coupler is on) push the shaft back as far as it will go. Hold it there while you tighten the coupler back up and then try it.

Posted on Jul 25, 2009

  • Don Maggard Jul 27, 2009

    Only thing I can think of to check is the black interruptor cup on the end of the motor shaft and make sure the little board is plugged in good.

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