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

[RSV_Ecosse]

I took my front and rear wheels off today in order to give the bike a long overdue top to bottom clean, getting into all the nooks and cranies with that Halfords Citrus Degreaser spray stuff. Cleaned everything up a treat.

Then I put the wheels back on and fastened the QR levers all back up.

However, the rear derailleur looks strange. The bottom part of the chain rubbing the top part and the derailleur itself. This is when the gears are on the wee cogs, first/smallest on the cassette and when the gears are on the small chainring at the front. As you move up the cassette at the back to the larger cogs the chains slowly move apart and don't touch by about the 5th cog. When on the big chainring at the front they don't touch at all.

That is probably as clear as mud so I took a couple of pictures.

*Note The pics were taken of the rear derailleur whilst the bike was upside down :-

The strange thing is all I did was take the rear off and clean stuff then refit it. And I can't recall whether it was even like this before I removed it either. The wheel spins ok when pedalling but it makes a loud noise.

Wish I hadn't touched the damn thing in the first place now. I have the "Midas touch" when it comes to removing anything from my bike.

*EDIT Forgot to say - It's a Pinarello FP1 with a 50/34 Tiagra Double compact.

 

[I am Spartacus]

Have you routed the chain correctly?
I can't tell from the pics unfortunately.

 

[dan_bo]

Looks like you're chain's far far FAR too long. Or off.

 

[dellzeqq]

the chain is over the highest (as in the smallest) sprocket. Is it on the small chainring?

You look to have much too much chain, but most chains will almost double back if you're going smallest to smallest. Could you also put up a picture of the rear derailleur with the chain going over the larger chainring.

 

[RSV_Ecosse]

Strange. It was all perfectly fine until I removed the wheel today. I rode to work on it this week ( Yesterday and Tuesday ) as normal. The chain length was spot on, can it really have grew xx inches overnight??!!!.

I'll grab another pic of it over the big chainring, by that i take it you mean the big chainring at the front ( cranks )?.

In the meantime, here are another couple of pics of it still on the wee chainring at the front but having moved it up a few gears towards the larger cog on the rear cassette. As you can see, it moves apart and doesn't touch when I do that :-

 

[I am Spartacus]

Have you knocked the derailleur from its seating as you replaced?
It attaches to the bike via the allen key you see in middle pic.
The bit with the writing on should be vaguely horizontal.

 

[RSV_Ecosse]

Just checked, nope - Not knocked anything out of place when refitting. My "Tiagra" writting on the body of the derailleur is almost horizontal like yours is when the chain is on the big chainring at the front but as soon as I drop it down to the wee chainring, it goes like it is in my previous pictures.

 

[I am Spartacus]

That might be normal... the derailleur stretching like that then
On 34 ring and on smallest sprocket.. which is a combination you dont use anyway 'cos of chain line..
again I may be wrong

 

[Coco]

Is it possible the degreaser has got into the derailler pivots and prevented something from springing in place? Can you move all the moveable parts in the detailler?

 

[PpPete]

Has the "b" screw come off the rear hanger?...it's supposed to push against it to get the angle of the top part of the mech right. If something got bent slightly out of alignment the screw can slip alongside the hanger and it all looks wrong.

 

[RSV_Ecosse]

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

 

[jpembroke]

If you have a double chainset put chain on biggest chainring up front and largest sprocket at the back. Your rear mech arm should now be at an angle of approx 45 degrees. If it's towards vertical or pointing back then your chain is way too long.

 

[RSV_Ecosse]

Did as you said, big chainring on front and large cog on back :-

 

[jpembroke]

Rear mech arm should be pointing forward about 45 degrees to ground. At the moment it is vertical. Try removing a link, reconnecting and and seeing where it is then. You may need to remove 2 links but better remove too few than too many to start with.

 

[peanut]

you should never use the largest chainring with the largest sprocket anyway but looking at your image it looks like your chain may be too long . Shimano recommend the following proceedure

with the bike the right way up put the chain onto the largest front chainring and the smallest cassette sprocket.
The two jockey wheels should be vertically inline with one another and directly under the centre of the rear wheel axle.
The chain is now the correct length.

You may need to add or remove links to achieve this.

'B' tension screw adjustment.
Put the chain onto the smallest chainring and the largest cassette sprocket.Turn the crankarm backward half a turn or so.
Then adjust the 'B' screw to get the top jockey wheel as close to the cassette sprocket as possible without touching.

Then repeat with the chain on the largest chainring and the smallest sprocket. Make sure the top jockey wheel doesn't actually touch the sprocket.

You may find that your rear mech return tension spring has weakened over time. It can be adjusted by dismantling the rear mech and tightening the spring but not a job for the faint hearted.

new mechs are cheap enough and are the heart of a good transmission system so if in doubt buy a new one.