Rear derailleur installation issue

gillian

Well-Known Member
Been trying to fit a new Shimano XT rear derailleur with 11-46 sunrace cassette but having issues with derailleur (tension?)
When in 46T ring the top jockey wheel sits just on the cassette teeth but as soon as you move down the gears it's terrible and doesn't hold position at all.
Any ideas what I've done/what needs done to resolve?
 

smutchin

Cat 6 Racer
Location
The Red Enclave
Looks to me like the cable is possibly too short, but I don’t know enough about the XT mech to say for sure and it’s hard to tell from your pictures.
 

fossyant

Ride It Like You Stole It!
Location
South Manchester
Adjust the 'B' Screw - it's a small screw at the rear of the mech (not the H/L Screws) that pushes onto a tab on your frame hanger - screw this in (clockwise) to move the mech away from the frame - it may be screwed out too far.

Your cable run will look OK then.
 

I like Skol

Hold my beer and watch this....
You haven't got the hanger tabs lined up by the look of things. There is a small nob/button on the back of the mech and this has to be 'hooked' against the tooth on the frames mech hanger.
unscrew the mech out of the hanger and try again. Do this while on the smallest 11T sprocket and drop the chain off the front chain ring and you wont have to wrestle against the mech springs so much.
 

smutchin

Cat 6 Racer
Location
The Red Enclave
Adjust the 'B' Screw
I would do this first, before attaching the cable. Once the position of the mech is correctly adjusted using both B and H-L screws (so the top jockey wheel is at most 1-2mm directly below the largest sprocket), I would then attach the cable, cut to the correct length.
 
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I like Skol

Hold my beer and watch this....
I would do this first, before attaching the cable. Once the position of the mech is correctly adjusted using both B and H-L screws (so the top jockey wheel is at most 1-2mm directly below the largest sprocket), I would then attach the cable, cut to the correct length.
No use doing anything until the mech is fitted correctly.
 

Levo-Lon

Guru
You haven't got the hanger tabs lined up by the look of things. There is a small nob/button on the back of the mech and this has to be 'hooked' against the tooth on the frames mech hanger.
unscrew the mech out of the hanger and try again. Do this while on the smallest 11T sprocket and drop the chain off the front chain ring and you wont have to wrestle against the mech springs so much.

Looks like that to me too
 

Sharky

Guru
Location
Kent
You're not alone with having technical problems installing bits. I often have to have more than one attempt before I suss out what is needed.
This maybe one of the reasons why 50% of my bikes are single speed or fixed.

Good luck
 

smutchin

Cat 6 Racer
Location
The Red Enclave
No use doing anything until the mech is fitted correctly.
Well, yes, fitting the mech to the bike correctly should be the very first thing you do. Then adjust the position using the B and L screws. Then attach the cable. Then adjust the H-L screws. Then adjust the indexing.

Sounds to me like the OP has skipped straight to the last step without going through any of the other steps.

ETA: have just looked at the pic again and I can see exactly what you mean - adjusting the B screw with the mech in its current position will make no difference whatsoever! (I was looking at it on my small phone screen earlier so it wasn't obvious)
 
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fossyant

Ride It Like You Stole It!
Location
South Manchester
If you zoom in on the first picture, you can just see the tab on the hanger - you shouldn't be able to see this as this is where the B screw sits against.

Undo the mech's main bolt and pivot the mech back. I just hope you haven't bent anything.
 

I like Skol

Hold my beer and watch this....
upload_2019-7-31_10-49-46.png

IMG_20190731_100903934.jpg


This is my son's bike, 11spd XT mech to show you how it should look. The B-tension screw doesn't work against the mech hanger, there is a kind of built in hanger extension as part of the derailleur.
 
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