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  1. #1
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    Problem with Reinstalling Shimano Deore LX Rear Derailleur (Noob!)

    I have a custom mountain bike that is based on a Saracen 'Team M.A.D' frame from the late 90's/early 2000's. Last week I ended up getting a couple of punctures in the rear tyre, so I decided to swap the tyre for one of those 'self-sealing' ones and sort a minor issue with the chain tension at the same time.

    When I removed the rear derailleur from the bike, there was a big 'ping' and some kind of spring loaded mechanism in the derailleur caused it to shoot out of my hands. After swapping the tyre and mounting the derailleur back onto the bike with the hex-key, I noticed it was no longer in the same position as before.







    The bit where it says 'Shimano Deore LX' is supposed to be kind of horizontal in line with the frame, like how I'm holding it above. But due to the spring-loaded mechanism, it seems there is no way to keep it in this position without it shooting back towards the left. I have tried everything but I cannot understand how it is supposed to stay in position.

    Underneath is a picture of the bike before I did anything to it. That is how it's supposed to look. I have watched a ton of videos on YouTube but none of them seem to make sense. If anyone could offer some assistance it would be most appreciated!

    Last edited by P650SE; 1 Week Ago at 10:43 AM.

  2. #2
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    It seems there was a problem with hosting images on Imgur. I have now changed the filehost so hopefully the pictures should remain visible!

  3. #3
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    It's either the spring at the main pivot or at the cage. I've dealt with main pivot springs many times back in the break-away bolt days. It's kind of a pain, but you can reset the main bolt (with some effort). The spring at the cage is unknown to me.

    Also your housing appears out of the derailleur as well.

  4. #4
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    Quote Originally Posted by Pisgah View Post
    It's either the spring at the main pivot or at the cage. I've dealt with main pivot springs many times back in the break-away bolt days. It's kind of a pain, but you can reset the main bolt (with some effort). The spring at the cage is unknown to me.

    Also your housing appears out of the derailleur as well.
    Thanks for the response. The thing I can't understand is, there was absolutely nothing wrong with the derailleur until I removed it. I just undid the bolt holding it to the frame and it kind of shot out of my hands due to the tension created by the spring-loaded bit. (The chain was still on the bike at this point, maybe I should have removed it first!)

    It seems odd how just from removing it, something could now have happened to the derailleur which prevents it from being reinstalled in the correct position... Which is why I wonder whether this is something considerably more simple. I should note I haven't done anything like this before, and what is obvious to most folks on here might be something I haven't tried.

  5. #5
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    Irrelevant to your question but why did you take take the derailleur off to change the tire?

    Is the derailleur installed correctly on the hanger?

    Maybe this picture of mine will help

    Sent from my SM-G950U using Tapatalk
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    I once had an awkward moment just to see how it felt

  6. #6
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    Quote Originally Posted by P650SE View Post
    Thanks for the response. The thing I can't understand is, there was absolutely nothing wrong with the derailleur until I removed it. I just undid the bolt holding it to the frame and it kind of shot out of my hands due to the tension created by the spring-loaded bit. (The chain was still on the bike at this point, maybe I should have removed it first!)

    It seems odd how just from removing it, something could now have happened to the derailleur which prevents it from being reinstalled in the correct position... Which is why I wonder whether this is something considerably more simple. I should note I haven't done anything like this before, and what is obvious to most folks on here might be something I haven't tried.
    Maybe just a coincidence. But you have to save derailleur to match the bike's age.

  7. #7
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    oh, i got this!

    What happened was that on your derailleur cage is a tab that effectively limits how far forward the derailleur cage (the thingy with the two rollers) can go forward. The tab broke, and allowed the tension spring that is inside the derailleur to unwind itself some into an unfavorable position.Problem with Reinstalling Shimano Deore LX Rear Derailleur (Noob!)-to3hgc.jpg
    I've circled the hole where the tab was.
    On some of those older (mid 90's era LX 500 series parts) the tab was actually threaded into the cage, some were pressed in. This is fixable, but it is not something I would recommend for a novice/beginner. And, given that 6-7-8 and even some 9 speed shimano all used the same pull ratio, you are probably better off buying a $15-25 derailleur new and putting that on.

    I've rebuilt probably 100+- broken derailleurs that have had this exact issue, and it still takes a long time, some swearing, occasional stabbing of my hand with a screwdriver and the constant thought of "why am I doing this?" Then I remind myself that I like fixing broken things and that is the only reason I do what I do.
    Deflated - buy parts to sell parts to buy more parts.. bikes are my drug of choice

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  8. #8
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    Quote Originally Posted by BurkC View Post
    Irrelevant to your question but why did you take take the derailleur off to change the tire?

    Is the derailleur installed correctly on the hanger?

    Maybe this picture of mine will help
    It seemed like a good idea at the time as I was having trouble removing the chain with an old tool. Of course I soon came to regret that decision!

    I do believe the derailleur is mounted on the hanger correctly; I have taken it off and put it back on about 5 times and I can't see any other way it could possibly be mounted.

    Quote Originally Posted by Jason Rides Bikes View Post
    What happened was that on your derailleur cage is a tab that effectively limits how far forward the derailleur cage (the thingy with the two rollers) can go forward. The tab broke, and allowed the tension spring that is inside the derailleur to unwind itself some into an unfavorable position.

    I've circled the hole where the tab was.
    On some of those older (mid 90's era LX 500 series parts) the tab was actually threaded into the cage, some were pressed in. This is fixable, but it is not something I would recommend for a novice/beginner. And, given that 6-7-8 and even some 9 speed shimano all used the same pull ratio, you are probably better off buying a $15-25 derailleur new and putting that on.

    I've rebuilt probably 100+- broken derailleurs that have had this exact issue, and it still takes a long time, some swearing, occasional stabbing of my hand with a screwdriver and the constant thought of "why am I doing this?" Then I remind myself that I like fixing broken things and that is the only reason I do what I do.
    Wow, thanks a lot! I'm not sure how you noticed such a precise detail like that from the pictures. I guess when you've had experiencing in fixing over 100 examples of the same issue, that's how you realise what is causing the problem! I had been doubting myself ever since it happened thinking there was a more common-sense explanation as to the reason I couldn't put it back onto the bike. Now I can see what caused all the trouble.

    Sounds like I'm out of luck with fixing this myself. If it's difficult enough for someone with experience, then I definately can't see me being able to do it as a complete beginner. Besides, I looked on eBay and it seems cheap enough to buy a new one.

    Is there anything specific I need to look for? The bike has 8 speeds. Ideally I'm just looking to spend as little as possible to get it working again, I don't intend on using the bike for anything serious. I see Shimano ones on here for as little as 6.99 GBP brand new. (RD TX35)

  9. #9
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    I would probably go for something a little higher quality than the RD-TX35. You can go up to a newer 9 speed derailleur and it will have the right cable pull ratio to work with your shifter. I would probably suggest a bit higher up the food chain, such as https://www.ebay.com/itm/Shimano-Ace...IAAOSwlR9a0IH0

    OR, you could try to find an older model part that is in good to new condition, but you may end up spending more as lots of "vintage" parts are starting to go for silly money. Stay away from the new shimano MTB parts that have a x000 (2000,3000) part number, I believe those changed the pull ratio a little bit so they may not play with your shifters well.
    Deflated - buy parts to sell parts to buy more parts.. bikes are my drug of choice

    FATTrailer for the kiddo

  10. #10
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    Quote Originally Posted by Jason Rides Bikes View Post
    I would probably go for something a little higher quality than the RD-TX35. You can go up to a newer 9 speed derailleur and it will have the right cable pull ratio to work with your shifter. I would probably suggest a bit higher up the food chain, such as https://www.ebay.com/itm/Shimano-Ace...IAAOSwlR9a0IH0

    OR, you could try to find an older model part that is in good to new condition, but you may end up spending more as lots of "vintage" parts are starting to go for silly money. Stay away from the new shimano MTB parts that have a x000 (2000,3000) part number, I believe those changed the pull ratio a little bit so they may not play with your shifters well.
    Thanks for the advice, I will have a search around and see what I can find. I appreciate the tips because I barely know anything about this stuff.

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