The garage door manual isn't clear about exactly how to check the chain tension. The tension differs if the manual "override" is engaged or not. When it's in "manual mode" (manually open/close the door), the chain sags too much when the door is open, but it's fine when the door is closed. However, if the door is connected to the motor (the motor opens/closes the door), the chain sags too much if it's open or closed (sags a lot more when the door is closed). This seems to match the manual better (it mentions the chain will sag a bit when the door is closed), so I think tension needs to be checked with the motor engaged, but I'm not sure. I don't want to over tighten the chain.

So, do you check tension in "manual mode" or not? If in "manual mode", should the door be open or closed?

The opener is a Sears Craftsman, which appears to be the same one by Chamberlain (the manual looks identical). The website that had the Chamberlain manual was Liftmaster.com.



  • 1
    Chain... Do you mean the door... or the automatic opener? Jun 26, 2019 at 0:59
  • Chain drive electric door opener is pretty old, isn't it? (I assume the door itself has steel cables, right? Just use the opener like it is and when it breaks get one of the newer ones. But when the opener is pulling up on the door one side of the chain will be taut and the other loose so it would make a lot of difference if the measurement is when the opener is pulling or not. Jun 26, 2019 at 1:09
  • 1
    The chain is what is attached to the motor (sprocket) that pulls the door up (some have belts, I believe). It's not THAT old--the previous owner kept the receipt--2010. Not adjusting it and waiting for it to break and replace the entire unit doesn't sound like a good option. Jun 26, 2019 at 1:20
  • There shouldn't really be tension on the chain unless the door is being held forcefully closed (which is normal, to an extent). It should be relaxed in other states. Chains run under static tension wear out motor bearings (and themselves) very quickly.
    – isherwood
    Jun 26, 2019 at 19:07
  • The tension on the chain is caused by stretching, or pulling it taught. Think about a bicycle chain. That chain is (always) under tension caused by pulling the back wheel away from the front (single gear bike). The more tension, the more taught/straight the chain is. And yes, too much tension will cause undue wear on the gears/bearings of the motor. Jun 26, 2019 at 23:31

2 Answers 2


I found virtually identical manuals for openers from Chamberlain & Liftmaster, so I called Chamberlain support. She said the procedure is:

  1. Have the door closed.
  2. Disconnect the trolley (that's the thing I was calling "manual override"). Don't move the door.
  3. Check the tension (1/4 inch above bottom of rail half way along the rail).
  • Please accept your answer to resolve this question. Some info on what the tension should be might be helpful.
    – isherwood
    Jul 21, 2020 at 19:10

While I think your manual should specify the conditions to check the tension, what I have done in the past is to check the tension with the door closed and the opener engaged, since that is the way it is likely to see the most use.

  • Thanks. Yes, I think the manual should be clear :). I'm leaning towards what you suggest as well. I found a Chamberlain door opener manual that is identical to the Craftsman one I have. If I can find a support number, I'll try giving them a call. My gut says all chain drive openers are very similar and are adjusted the same way. Jun 26, 2019 at 23:25

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