Why is my rear derailleur like this???!!!

[RSV_Ecosse]

Thanks for the info folks, appreciate it. Still not sure where this B screw is though.

It's really weird, Can't understand why this has suddenly came to light after months of riding it, all I did was remove the rear wheel and then replace it again. I did fit a new SRAM chain a few months ago after my original snapped but at the time I laid the old one down ( which wasn't that "old" to be honest and didn't have that many miles on it hence I would not have thought it had stretched much ) next to the new one and removed a couple of links from the new one so it was the same length as the old one, refitted it all and everything was fine.

To be honest I think it might be an answer just to take it to my LBS and get them to sort it out as I am baffled as why this has happened. I will whip a couple of links out, one at a time, to see if that helps before I phone them though.

you should never use the largest chainring with the largest sprocket anyway

I've read this sort of thing before, it's to do with the line the chain runs in, yeah?. But what confuses me is essentially what you are saying is that there are some gears on my bike I can't and should never use?. E.g. if I'm descending a steep hill at a fast speed, say above 30mph, I usually just click through the gears when I'm on the big ring at the front so that I go all the way to the big cog at the back so that my legs are not spinning at a million miles an hour and I can still pedal to keep the speed up. So essentially I shouldn't be doing that, using all the gears?. I should just freewheel down the hill once my legs start spinning too fast?.

/confused

 

[jpembroke]

you should never use the largest chainring with the largest sprocket anyway

True, but it is a good way of revealing if your chain is too long. Obviously you shouldn't ride a bike in this gear.

 

[Bayerd]

I've read this sort of thing before, it's to do with the line the chain runs in, yeah?. But what confuses me is essentially what you are saying is that there are some gears on my bike I can't and should never use?. E.g. if I'm descending a steep hill at a fast speed, say above 30mph, I usually just click through the gears when I'm on the big ring at the front so that I go all the way to the big cog at the back so that my legs are not spinning at a million miles an hour and I can still pedal to keep the speed up. So essentially I shouldn't be doing that, using all the gears?. I should just freewheel down the hill once my legs start spinning too fast?.

/confused

You'll be on the smallest cog at the back when doing this. You shouldn't need to use the big to big combo at all as using a mid to mid selection will give you a similar gearing.

The way I understand it, when using the smallest front ring you should use the largest 3 at the rear. When using the middle ring you can use the biggest to about 5th. When using the largest front ring you should use the smallest 3 cogs on the rear. The reason for this is to reduce chain wear.

 

[youngoldbloke]

E.g. if I'm descending a steep hill at a fast speed, say above 30mph, I usually just click through the gears when I'm on the big ring at the front so that I go all the way to the big cog at the back so that my legs are not spinning at a million miles an hour and I can still pedal to keep the speed up. So essentially I shouldn't be doing that, using all the gears?. I should just freewheel down the hill once my legs start spinning too fast?.

/confused

- I'm confused too - don't you mean on big ring at front click through to small cog at back - which is a perfectly sensible OK thing to do. There is no law saying thou shalt not use big/big or small/small, but if you do you might find the chain fouls the cage of the front changer due to the extreme chain line, and some say that wear on the cogs/chainrings might be accelerated if you make a habit of it

 

[RSV_Ecosse]

Whoops!!!. Bit of a Blonde moment there - I now realise I mean't small cog at the back for descending at speed, not the big 'un.

Sorry!!. Thanks for clarifying that.

 

[peanut]

I've read this sort of thing before, it's to do with the line the chain runs in, yeah?. But what confuses me is essentially what you are saying is that there are some gears on my bike I can't and should never use?. E.g. if I'm descending a steep hill at a fast speed, say above 30mph, I usually just click through the gears when I'm on the big ring at the front so that I go all the way to the big cog at the back so that my legs are not spinning at a million miles an hour and I can still pedal to keep the speed up. So essentially I shouldn't be doing that, using all the gears?. I should just freewheel down the hill once my legs start spinning too fast?.

/confused

think you are getting confused.

The smallest sprocket at the back is the fastest whatever chainring you use at the front.
If you are riding downhill you should be in the largest ring at the front and the smallest at the back ie the highest ratio.

The reason you should not use big ring big sprocket is because of bad chain alignment and your rear mech will be on its limit of travel .
Better to find a similar gear ratio by using the small chainring and a larger sprocket.

 

[peanut]

n00b question - Where's the "B-Screw" and what am I looking for?.

the 'B' screw is on the backplate of the rear mech fixing bolt. It adjust the rear mech return tension which keeps your chain tight on the sprockets .

 

[peanut]

To be honest I think it might be an answer just to take it to my LBS and get them to sort it out as I am baffled as why this has happened. I will whip a couple of links out, one at a time, to see if that helps before I phone them though.

yes that sounds the best bet as you clearly have no understanding of setting up and using gears.
Don't remove chainlinks it will solve nothing. Follow the Shimano guide

 

[bonj2]

i suggest either:
* before you decided to service it, you'd never actually used the small chainring, so this problem never surfaced
* you took the chain off but when putting it back on inadvertently picked up a completely different one

but whatever it was like before, and wherever the solution the mystery of why this problem has suddenly materialized may lie, there's no escaping the fact that the chain on that bike is far, FAR too long. That's a physical fact, and needs no qualification by way of the sequence of steps by which that may have come about.

Take the chain off. Leave the back wheel on.
pass the chain round the biggest sprocket and the biggest chain ring but NOT round the mech. Mark how long the chain needs to be to do this with your thumb. The ideal chain length is this length plus two links. You'll be taking quite a few links out.
See http://www.parktool.com/repair/readhowto.asp?id=26 (scroll down to "Chain Sizing - Largest Cog and Largest Chainring Method").
Put the chain back on.
Adjust the B-screw as here: http://www.parktool.com/repair/readhowto.asp?id=64 (scroll down to heading "B-Screw Adjustment")

take to LBS if still not happy/confused.

 

[RSV_Ecosse]

Follow the guide that I spent half an hour typing out for you.

LOL...Could you not have just did the good auld "Copy & Paste"?.

Will get on with the link removal after breakfast and report back.

 

[peanut]

LOL...Could you not have just did the good auld "Copy & Paste"?.

no because I didn't think you would understand the Shimano technical guide so I wrote it out in simple language for you


The Shimano technical guide is a pdf file with a picture guide and isn't easy to follow tbh so I thought it would be easier for you to follow a written guide

 

[RSV_Ecosse]

LOL....no worries. I'm fine using the gears but when it comes to adjusting anything or servicing the thing I just haven't got the know-how or experience to do so. I suppose this will come with time.

Strange thing is I can service and repair a 1000cc Superbike without batting an eyelid. I removed and rebuilt my rear Ohlins shock last month so it's not that I'm a complete mechanical failure. Except when it comes to cycling.

 

[MartinC]

It's hard to tell from the photos but your mech looks bent to me. The parallelogram looks like it's been twisted downwards. Try posting some more photos from different angles.

 

[Speck]

no because I didn't think you would understand the Shimano technical guide so I wrote it out in simple language for you


The Shimano technical guide is a pdf file with a picture guide and isn't easy to follow tbh so I thought it would be easier for you to follow a written guide

He should have had Campag Nick

 

[MartinC]

Looked at your pictures again. Is the problem that the B Tension spring has broken? If you try and move the bottom end of the parallogram down and back by hand (like you do when you take the wheel out) you should feel some resistance and it should spring back when the pressure is off.