I noticed one day that the garage door could only open two feet then it stuck. Got in from the side door and noticed the inner slide of the T-Rail was totally ripped as below.
 | Inner Slide Ripped
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| |  | Outer Carrier De-Railed
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Got on eBay and placed a quick order of Liftmaster 41A3489 carriage trolley assembly. A few days later, the parts came with following pieces.
 | Garage Door Opener
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| |  | Garage Door Opener
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 | From E-Bay
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| |  | From E-Bay
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Found a Saturday and went through following steps:
- Open the garage door and keep it open. Took a 2x4 to block the door from falling
- Pull down the manual release rope and remove the lock wire and the pin to detach trolley and garage door.
- Mark on the tension screw to assure that I can tight the screen to restore the original tension of the chain.
- Loose and Remove the tension screw
- Remove the link clip-on spring and the link cap to disconnect the chain
- Remove the stopping screw and detach the T-Rail from the garage door opener
- Very gently lift the loose end of the T-Rail to slide the broken trolley out
- Slide the new trolley back in
- Reverse previous steps to tights all the screws
- Remove the 2x4
- Worked!
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Step 1: 2x4 to block the falling door
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Step 2: Disengage door
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Step 3/4/5: Release the tension and chain spring clip
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Step 6: Stopping screw and detach door opener
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Step 7: Slide trolley out
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Step 11: Completion
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 | The torn piece
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This is a super easy job. It took me about an hour to compete the tested to assure the whole thing worked. Well, there is small difference. By comparing picture of step 3/4/5 and step 10, I noticed the washer got changed from the right side to the left!
