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Weak spring tension on the derailleur will result in sprockets wearing out faster
#1
On one bike I have either the bottom of the range Shimano rear derailleur, or an imitation copy of the bottom of the range Shimano rear derailleur. The spring tension is weaker than many other rear derailleurs. The chain sags more than it should.

With a derailleur like this, the chain rides up on the sprockets more than it does with a derailleur with stronger spring tension. This results in the sprockets wearing out faster. The sprockets don't need to be very worn, before the chain starts jumping teeth.

I will not buy this type of derailleur in the future. I will buy derailleurs with stronger spring tension.

If anyone reading this notices their chain sags too much, this may be the cause. You may also find your sprockets wear out too fast.

There are not-too-expensive derailleurs available with stronger spring tension.
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#2
(08-12-2022, 08:33 AM)ichitan Wrote:  On one bike I have either the bottom of the range Shimano rear derailleur, or an imitation copy of the bottom of the range Shimano rear derailleur. The spring tension is weaker than many other rear derailleurs. The chain sags more than it should.

With a derailleur like this, the chain rides up on the sprockets more than it does with a derailleur with stronger spring tension. This results in the sprockets wearing out faster. The sprockets don't need to be very worn, before the chain starts jumping teeth.

I will not buy this type of derailleur in the future. I will buy derailleurs with stronger spring tension.

If anyone reading this notices their chain sags too much, this may be the cause. You may also find your sprockets wear out too fast.

There are not-too-expensive derailleurs available with stronger spring tension.

You may be able to adjust the pulley cage tension. Many derailleurs were designed to cover a large sprocket size range and can be adjusted for a smaller racing cluster or a larger touring cluster for road bike designs. I'm not sure if the same applies to mtb mechs.
My earlier mechs have 2 or more holes which allow for more or less tension.
If you can set the wheel up so that it is more to the rear of the drops (applicable to horizontal drops with room for adjustment) you can take up some chain slack in that manner also and avoid derailleur adjustment.
There is one other issue that may be part of the issue: chain wear. I would have the chain checked for wear just to be sure it is not exacerbating the problem regardless if you get a new derailleur or not.

For reference, what is the Shimano (or other manufacturer) model number of that unit?
Take care,
Jesper

"I am become Death, the destroyer of bicycles." NJS
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#3
Whenever I buy a replacement derailleur, I plan to buy a different type. That is the end of the problem for me.

These come on some new bikes. They have the Shimano name, which helps sell the bike. But a lot of people don't know these cheap Shimano parts are poor quality.

I believe Shimano and many other companies are making the lower end parts to wear out or break sooner, so they sell more spare parts, and make more money. If you want quality, you are supposed to buy the expensive models.

Of course there are derailleurs made by companies other than Shimano, which some of us might buy.

Here is an image of the derailleur.

   
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