WTD 7 speed rear derailleur

[petemaz]

Trying to resurrect my 20 year old mongoose hardtail into a commute bike for work. Currently has a knackered shimano lx deore r/d which needs replaced and struggling to find anything online that looks compatible. Anyone got something lying around they could sell me? Cheers

[HaYWiRe]

I thought derailiers were reasonably universal regarding speeds aslong as the cage in the right size for the cassette?
After all dont the shifters do all the indexing?

[petemaz]

That's what I'm not sure about so was going to replace like for like if possible. As I said it's an old bike so not sure if a new derailleur would work or not!

[slarge]

Pretty sure 7,8 were the same. 9 also but the thinner chain meant a thinner cage.

An 8 speed cassette is wider than 7 though so you'd need a new wheel to upgrade.

I'll have a look in t he magic box in the garage for stuff that I will never use and never throw away...

[fatbikephil]

A 9 speed mech works on 7 or 8 speed - 7 speed is the same spacing as 8 speed and whilst the jockey wheels on a 9 speed mech are narrower it doesn't matter.

[Tanglefist]

This is a great resource for this stuff;

http://blog.artscyclery.com/science-beh ... atibility/

Short version; older shimano mechs (6-9) will work fine because the pull ratio is the same. It just does what it's told by the shifter with regards to number of sprockets and the distance between them. Since you're not changing the shifter, that doesn't matter. The only other factor is cage length - mountain bike ones tend to come in medium or long. In general terms, medium's will do up to a 32t big sprocket on the cassette and a long will do up to 36t also it's actually dependant on the size of the front chainrings as well.

[petemaz]

Thanks for the info folks, very useful.

[slarge]

Pete, I found a 9 speed XT rear mech that I will never use. Needs new jockey wheels. Do you want it?

[petemaz]

Arggghh! I ordered an 9 speed deore off eBay just last night! Thanks anyway slarge!

Pete, I found a 9 speed XT rear mech that I will never use. Needs new jockey wheels. Do you want it?