Forum help please 😀
KTM Aera Comp 2016. The rear derailleur was jumping around and needed replacing. I bought a brand new Deore XT M781(exact modelas before) 10 speed unit from Wiggle. Fitted it yesterday. Wh6ne going into the largest ring it makes a nasty grinding noise. Seems the jockey wheel is too close to cogs. When I screw the "B" adjuster the screw has no impact and makes no contact. There is a small plastic spacer on the "B" screw, I took this out and it now connects a very small bit when screwed fully in. Still makes a small grinding noise when shifting to largest cog. Any suggestions ? Think I am going to put the spaceer back in and start again from scratch. Unit it seated as far back as possible. I also added a new 10 speed chain. The chain is correct type and shifts well with all gears except this largest cog. Chain seems correct length (I removed 3 links)
Why was rhe previous mech jumping around? How old is the bike? I wouldnt expect to have to replace a rear mech on a 2016 bike unless it got damaged on the trail.
Sounds more like set up (in both cases?) Is the mech fitted correctly on the hanger?
Cable going into rear mech too short?
I cant think its down to the b screw being too short.
Pics would help though.
Like nairster says, If the b screw doesnt make contact then the mech has to be on the hanger wrong, or there's something wrong with the hanger or mech. Its the b screw that defines the position of the mech on the hanger, so it has to be in contact. Put another way, if you didnt have the frame in the way you can rotate the mech about 270 degrees around the hanger, but theres only 1 spot, the one where the b screw hits the b tab, thats correct.
This sounds a bit like what happened to me a few years back, if I remember rightly I removed a link from the chain to sort it out.
Sorted now. Doh..!! I had slightly underhung the mech to the frame. Reset it and "B" screw working perfectly. lesson learnt. Ben's post made me think I should take it all apart and start again.
thanks for the replies.
Chain seems correct length (I removed 3 links)
your chain measuring technique concerns me.
pics may generate some useful advice
your chain measuring technique concerns me
Not sure I follow you ? I didn't say how I measured my chain.
I offered it up against the old chain which came on the brand new bike. The new chain I have fitted was 10 speed and 116 link (now 113). I then confirmed the length by offering it up with the chain on the largest cog at the back and largest chainset on the front.
