Changed derailleur but...???

[Frimley111R]

Just changed the derailleur on my Boardman MTB but the top jockey wheel is hitting the cassette, no idea why. What am I doing wrong?...

[Davie]

Wind in that little Allen headed bolt that pushes against the derailleur hanger on the frame. That'll drop the rear mech down. There's alignment tools for most set ups but go with about 3mm clearance for starters. You'll likely need to tweak the cable tension etc afterwards again.

[frisbee]

Shimano have really detailed setup instructions for every component they make. Just Google the part number.

[Frimley111R]

Davie said:

Wind in that little Allen headed bolt that pushes against the derailleur hanger on the frame. That'll drop the rear mech down. There's alignment tools for most set ups but go with about 3mm clearance for starters. You'll likely need to tweak the cable tension etc afterwards again.

Ah got it, thank you.

Yes, it goes to the smallest cog on the cassette but misses the three largest.

[Frimley111R]

frisbee said:

Shimano have really detailed setup instructions for every component they make. Just Google the part number.

Ok thanks, nearly there. if only I was 12 years old again, when this type of thing took me 5 minutes!

[POIDH]

As above, you need to pull derailleur backwards using the 'B-tension' screw.
Download the Shimano instructions or fire up a Shimano derailleur instruction on YouTube