bishop130771

Hi All
Sorry to ask but I'm pulling my hair out with the acera 7/8 speed derailleur set up! Basically running 11-40 cassette (checked the derailleur is rated for up to 40 and it is apparently). End points seem ok (Is set these up manually without chain by pushing derailleur to the largest cog). Chain length is correct and I've got the indexing pretty much there now.
The issue is in the lowest gear (40T cog), I can't get the upper jockey wheel to stop touching the sprocket and no matter what I do with the b screw it doest move the cage at all.
Am I missing something here, is it the derailleur that's not suited?!

Andrew R Stewart 

Pushing the cog size to it's limits will sometimes show issues that are not present if you keep away from that limit. Can you shorten the chain and still have it fit around the largest cog/ring combo? If so this will rotate the cage and drop the guide pulley away from the large cog.

But a question- What model version of Acera der do you have? I wonder if you have confused chain wrap capacity with large cog capacity. Chain take up is often in the 35-40 "teeth" (actually links) range. My experience with your der family is that they usually have a 34T large cog limit. Your problem is exactly what I would expect you did confuse the two specs. Andy

bishop130771

Thank you so much for your reply it’s the m360 derailleur….sounds like I have got the max tolerance mixed up then?
can you recommend an 8 speed that would work with 40?
many thanks

Andrew R Stewart 

I no longer bother to learn new parts specs if I don't have to deal with them so I don't know the M360's specs. My quickie interweb search suggests this der has a 34T max cog and a 43 tooth chain wrap capacity.

You might try to find a SunRace M91 der. While it meets your needs it isn't in stock at the two LBS suppliers that I have access to. Good luck. Andy (who runs triple cranks to get his low gears)

70sSanO

You can always get a derailleur hanger extender like a Wolftooth RoadLink. I have them on my mountain bikes to be able to run a 40t.

You might lose a bit of shifting performance/speed on the smallest cogs, but for mtb riding it has never been apparent to me.

John

SoSmellyAir

The problem is even some legitimate shops mix up the two specifications, e.g., REI:

Shimano Acera M360 8-Speed Rear Derailleur | REI Co-op

Both max rear cog and total capacity are listed as 43T, whereas the former should be 32T or 34T.

mikethe

Maybe playing with the chain size?

Andrew R Stewart 

As someone who has suffered with dyslexia since childhood I fully know about this "typo" error. Andy

bishop130771

thanks guys all very confusing to a relative novice! I've bitten the bullet on a extender to see if that cures things, I'm loathed to buy another mech nor a cassette given the cost! I like my single chain rings so I feel I really need the 11-40 range at the back...
It's annoying as I have an xt 11 speed sitting around brand new but my wheels hub won't take an 11 speed cassette!

andrewclaus

It probably won't work going that far out of range, but I've seen some people remove the B screw and put it in backwards to get just a little more range, say 36T vs 34.

Andrew R Stewart 

I hope you don't find that you trade off large cod issues with small cog ones. We've installed a few der hanger tab extenders and find that the shifting suffers with the smaller the cog. Andy