Chain lock

gary.hounsome

Hi all,

I've changed numerous components on my bikes over the years so have some technical experience. I've been late finishing off my winter bike after stripping it in the summer, I have already changed the chain and cassette and remember cutting the new chain to the length of the old. Bolted the rear derailuier back on and installed new cables.

now that I've come to tune the shifting, once in the big ring the chain will not move the lowest four gears at the back, the rear mech just locks up and is only released when shifting back to a higher gear.

I thought at first maybe the chain was too short but I measured it against the previous one!

Any advice much appreciated. Cheers

sungod

some rear mechs have a tab that rotates around the mounting bolt that needs to press against a corresponding bit on the mech hanger, if you don't get it correct the cage will just swing up into the cassette

less likely, check the chain is running on the jockey wheels and also is not going the wrong side of one of the pins/tabs on the cage

gary.hounsome

The chain is OK as I've checked it against my other bike. Is the tab your talking about a screw just above the mount bolt? I'll take it off and have another look

sungod

this sounds like the b-adjustment screw, the end should press against the tab, if it isn't then that's a problem

this may help you...

http://www.parktool.com/blog/repair-help/rear-derailleur-adjustment#article-section-5

ic.

Yep, sounds like B-screw to me, I think your mech is hitting the cassette