Derailleurs..

[keithmac]

Hello all, my lad needs a new derailleur. It's an 8 speed Shimano cassette.

What do I have to measure to get a new one, any Shimano 8 speed will do or is this a long or short cage etc?.

Need a new shifter as well but same again, if I go for an XT shifter and derailleur will they be a straight forward fit?.

 

[DCBassman]

Any Shimano MTB derailleur from RD-M310 onward will do fine. An RD-M410 is what looks to be there at the moment.For something more snazzy but still inexpensive-ish, an Alivio RD-M4000 will also be good, it's capable of 9-speed should upgrade be required. In practice, the RD-M410 will also do 9-speed - my now-sold Trek 800 Sport is running 9 with this mech.

 

[keithmac]

Thanks for the reply!, he's happy with the gearing as is.

I've straightened this one a few times now (god knows what he does with it) but this time it's due replacement.

Will have a mooch about now I know what I'm looking for.

 

[Cycleops]

It takes quite a force to bend a derailleur so I should check the hanger as that will usually bend first.
The shifter might just need flushing out with WD40 if it's not working correctly.

 

[DCBassman]

flushing out with WD40

Or better yet, GT85, as that's actually a lubricant as well as a water dispersant.

 

[keithmac]

The whole thing is well past it's best.

It is bent, which is pretty amazing really.

I like GT85 for cleaning, then a few drops of 3in1 or gear oil for lubricating.

 

[Big John]

When you say "It is bent" I presume you're talking about the hanger? If so then it must be well bent because usually you need a hanger alignment tool (or at least a home made one) to check that. If you can visually see it then it's proper bent. You can either replace it or try and straighten it but without an alignment tool it ain't easy. Go easy. Those things snap. An alignment tool not only checks whether it's bent or not but you use it to get it straight again. Your LBS will straighten it for a few quid. If you decided to replace the hanger (easy to do) then you can either find them on the net or try your LBS. I think the one you have is a popular one. There are literally scores of different hangers ☹️