XT M739 rear mech jockey wheel hitting underside of cassette

[REKIBorter]

I have an 8 speed XT M739 SGS rear mech and a SRAM PG850 cassette 11-32T. The specs say the mech should work with this combination even though it is the extreme end of its capacity. The front chain rings are 22-32-42 which are also within range but again at the furthest end.

In the largest gear the top jockey wheel hits the underside of the cassette. I have adjusted the 'b' screw until it is screwed right in but still happens.

Any words of wisdom out there in RB land, or should I give up and get a 11-28T cassette?


XT M739 SGS
Front difference 20T
Total capacity 39T
Max. rear sprocket 32T
Min. rear sprocket 11T

 

[lewis1641]

are the top and bottom jockey wheels in the right way round? i learned the other day that they are different top and bottom

 

[REKIBorter]

Have no reason to think they are not in the right way round. The mech and cassette worked together on another bike without any problems.

 

[Radar]

Take it off, put all the screws back in their 'factory settings', make a cup of tea, watch a movie (sorry no Charlton Heston films on this weekend - even though the laws of Easter film scheduling dictate that there MUST be a biblical epic/Spartacus/Romans were bad film on terrestial TV). Then rebuild and the magic pixies will have sorted it. Always works for front mechs, see no reason why it shouldn't for rears.

 

[legrandefromage]

add a couple of chain links

 

[fingers]

Have you adjusted the 'b' tension screw?

 

[Skeelsie]

Another vote for chain length.

 

[andrewl]

Its all about chain length.

The often misunderstood B tension does not move the jockey wheel closer/further from the cassette.

 

[andrewl]

add a couple of chain links

I was thinking remove one...

 

[chaser]

Removing links will make it worse.

Try the b tension screw, it's the one behind the pivot bolt that stews into the dropout.

The other posibility is that the spring on this pivot is weak or the pivot is sticky.

Hope this helps.

Chaser