Replaced drive gear but cannot get door to operate properly after reassembly

[bfollowell]

I have an older model Craftsman 139.53673SRT3 garage door opener that was manufactured by Chamberlain. Even though it is twenty years old, this opener has been working fine until the door started slipping recently. It didn't take long to find that the nylon drive gear was almost completely stripped and needed to be replaced. I am very mechanically inclined and this seemed to be a fairly straight-forward part replacement. I ordered the LiftMaster 41A2817 Replacement Gear Kit and proceeded to replace the drive components of my opener. Everything went very smoothly until after reassembly.

Now that everything has been properly reassembled, the trolly will not move more than about 1 foot. I have the trolley in a position that, if the door were connected, would have the door open at about the mid-point. Likewise, the limit switch is mid-way between either end stop. When I connect the chain and attempt to operate the door, the door will immediately lower about 1 foot and then reverse to it's original position. At no point does the limit switch come anywhere near either stop. I have verified that the switch itself is opening and closing electrically so I do not believe that is the issue. The photo-eyes are not blocked, and seem to operating normally. The light does not flash at any point which would indicate somethign blocking the photo-eyes or a problem with back pressure.

I've read through the troubleshooting information included and followed all of the adjustment steps included with the gear kit but cannot get my door to do anything more than bounce back-and-forth this 1 foot distance.

Does this ring any bells or sound like anything that I may have missed that would be causing this? I will call someone in if I need to but this seemed like a pretty straight-forward parts swap and I hate to give up when I am so close. Any assistance anyone might be able to provide would be most appreciated.

Thank you.

- Byron Followell

[bfollowell]

I may have finally found my own answer. After much Googling, I found several different posts on other forums/sites of others having an issue pretty much exactly like mine. The most likely cause was that the sprocket cover was not reinstalled or was not reinstalled properly. Well, I know mine isn't reinstalled because I intentionally left it sitting on my work bench. I was under the impression that it was nothing more than a glorified dust cover and I wasn't going to put it back on until I was sure I was done. From what I read, I gather it turns with the sprocket and part of it rotates through the RPM sensor. Without the cap in place, the door will not operate properly and will act much as mine has been. When I wake up tomorrow afternoon, I'll reinstall the cap and, hopefully, that will be the fix. Then I can just make any limit and force adjustments needed and my door will be back in operation.

I'll post back here what I find out.

- Byron

[bfollowell]

OK, well, the good news is that my garage door is working properly again. The bad news is that I was even more careless and silly than I had originally thought.

I was mistaken. The other posts I'd read concerning this issue were pertaining to the interrupter cap on the end of the motor shaft, not the sprocket cover. I thought maybe I had not pushed the motor shaft far enough forward before tightening the collar and reinstalling or that maybe I hadn't put the cap on firmly enough. In my case, I just plain old missed reconnecting the cable connector to the RPM sensor. It was sitting right, exactly beside the four prongs in such a way that, when looking at it from the side, it looked like it was connected, but wasn't in my case. Just a simple case of rushing to get a job done instead of paying attention to what I was doing.

So, I rechecked all my positioning, made certain the interrupter cap was in place, reconnected the RPM sensor connector, and everything worked perfectly. A couple of minutes adjusting limits and I was back in business.

So, if anyone ever has an issue with your door only moving 9" or a foot or 18", stopping, and returning to its original starting position, the key is not the distance that it is moving but the time the motor is running. Without a proper signal from the RPM sensor, the motor will turn for 3 seconds, in both directions, then stop. And it won't do anything more until the problem is corrected. Whatever you eventually find as the problem, it will almost assuredly be related to the RPM sensor.

I hope this helps someone else in the future that may be experiencing the same problem I did.

- Byron

[GarageTech]

OK, well, the good news is that my garage door is working properly again. The bad news is that I was even more careless and silly than I had originally thought.

I was mistaken. The other posts I'd read concerning this issue were pertaining to the interrupter cap on the end of the motor shaft, not the sprocket cover. I thought maybe I had not pushed the motor shaft far enough forward before tightening the collar and reinstalling or that maybe I hadn't put the cap on firmly enough. In my case, I just plain old missed reconnecting the cable connector to the RPM sensor. It was sitting right, exactly beside the four prongs in such a way that, when looking at it from the side, it looked like it was connected, but wasn't in my case. Just a simple case of rushing to get a job done instead of paying attention to what I was doing.

So, I rechecked all my positioning, made certain the interrupter cap was in place, reconnected the RPM sensor connector, and everything worked perfectly. A couple of minutes adjusting limits and I was back in business.

So, if anyone ever has an issue with your door only moving 9" or a foot or 18", stopping, and returning to its original starting position, the key is not the distance that it is moving but the time the motor is running. Without a proper signal from the RPM sensor, the motor will turn for 3 seconds, in both directions, then stop. And it won't do anything more until the problem is corrected. Whatever you eventually find as the problem, it will almost assuredly be related to the RPM sensor.

I hope this helps someone else in the future that may be experiencing the same problem I did.


- Byron

You are correct, it is in fact an RPM sensor and is required for the GDO to run.