Rear derailleur replacement question.

[Pete Biggs]

It's easy once you get the idea. You need Allen wrenches (usually 5mm and

3mm) and a small screwdriver. It's good to replace the inner cable at the same time, so you'll want decent cable cutters too. If you don't want to break the chain, the rear plate of the cage needs to be removed via the jockey wheel bolts. You'll find full instructions online for fitting and adjustment.

Probably any Shimano long cage derailleur will be fine. Look for one described as 8 or 9-speed. This will also work with 7-speed.

~PB

[Death From Above]

I have a mongoose mountain bike with 3 gears in the front and 7 in the back. The rear derailleur is all bent up and needs to be replaced.

Is it easy to do? Do I need special tools? What kind of rear derailleur should I buy? Are they any good cheap ones online?

[landotter]

You can find instructions here:

Something like a $20 Shimano Altus will do you just fine. Just use your search engine for the best deal.

[Pete Biggs]

A new derailleur does not need a new chain, and a new chain may not work with the old sprockets if they are well worn.

~PB

[Michael Press]

Some notes in addition to the good advice tendered so far.

• You can do a good job installing the first time out.

• Read the instructions thoroughly before installing.

• Probably should install a new chain.

• Heed the advice about making the cable run good.

• Be sure to set the B limit screw so that the near jockey pulley is close to the largest gear in back.

• The high and low limit screw settings are important. Get them right.

• The limit screw that stops the derailleur closest to the spokes is critical. It must be set out far enough to allow the chain onto the largest gear, but tight enough to prevent the chain going into the spokes. When you think it is correct, put the chain in the smallest gear in front and the largest gear in back, turn the crank and push the derailleur body with your thumb to see if the chain slips over the top of the largest gear and into the spokes. Adjust as necessary.

[Mike Jacoubowsky]

But if the derailleur was "all bent up" as described in the original post, it's quite possible the chain might be twisted, or that it could have been a separating link that caused it. In any event, checking the chain for damage (twists or tight links) as well as wear would be a good idea.

--Mike-- Chain Reaction Bicycles

[Bernhard Agthe]

If you use your bike a lot I wouldn't go for a Shimano A* (Altus, Alivio,...) because you may or may not be lucky ;-) I used one of the "Deore" groups RD and got *much* better performance out of it - as well in shifting accuracy as in little running resistance. Actually I only had two A* and one Deore LX and I'll never again want an A* ;-)

Please, before you mount your new RD, check the alignment of the derailleur hanger - if it's bent you'll never be able to adjust your derailleur correctly...

Good luck...