Can't shift to granny ring – need some help, please
Ian, it was parallel, but I twisted it over to see if I could get that extra mm just to make it shift. The chain now rubs on the mech, but still won’t shift. Can’t see how I can get the mech to actually line up with the small ring, due to the clash of the mech with the seat tube.Posted 4 years ago
Not installed a new BB, but it had new cables just before i started using it again.
It had a service at the same time, and wasn’t shifting down after the service, but I didn’t get chance to take it back.
I wonder if they changed the BB at the service, although I definitely didn’t get charged for one, and it wasn’t mentioned when I picked it up.
Robdob, that sounds like the most obvious cause. Those 3mm would make all the difference. I’ll investigate, cheers.Posted 4 years ago
I have taken the caps off the crank bolts, and realised that my ISIS crank puller wont work on a hollowtech crank 😳
It looks pretty gnarled up in there though, with mash up aluminium. I wonder if the crank bolt has been wound so tight it has crushed and moved the crank in too close to the BB. The cranks have been really creaky going uphill out of the saddle.
Time for the LBS I think.
Cheers for the help.Posted 4 years agochrisdwSubscriber
Obviously its nothing to do with cables or tension or limit screws people!
The mech is as far over as it will go (touching the seat tube), no matter what you do to cables or screws its not going to move the mech any further! So it must be that the chainrings are too far in. Whack a spacer in the BB, problem solved 🙂Posted 4 years ago
Even with no tension at all in the front mech cable, it won’t shift to the smallest ring.
It appears that the black plastic body of the mech is clashing with the seat tube, almost acting like a limit screw.
It used to shift down when I used to ride it about 5 years ago, but since I started using it again a few months ago, it has never shifted down.
Where am I going wrong?
You can see the small mark on the seat tube on the second pic, where the mech touchesPosted 4 years agoconkersMember
Has the mech been raised?Posted 4 years ago
The indentation of the outer cage plate should push the chain off the middle ring. It then widens at the bottom so it doesn’t rub while in the granny ring.
Try repositioning the mech lower down the seatpost and swing it out checking that the cage clears the big ring by about 1mm or as close as you dare. If you’ve put a larger big ring on then you might have a problem.
Conkers, yes it is set up with 1mm clearance on the big ring.
I managed to get the cranks off by putting a woodscrew through the hollow crank bolt on the other crank, and using the crank puller (with a hole punch extender) to get the crank off.
There is no wear on the splines connecting the BB to the crank, so that can’t be squashed up, as I had suspected. There does appear to be more BB axle poking through on the non-drive side compared to the drive side. Is there a way of adjusting the position of the axle in the BB so that more pokes out on the drive side?
That would solve my problems.Posted 4 years ago
Having not taken a BB out before, I was a bit confused as to where or how to install a spacer.
I have now got the BB out, and have figured it out. There is only about 10mm of thread on the cartridge, so a 3mm spacer will reduce that to 7mm, which is a bit of worry. There must be a lot of force going through that thread.
I presume BB spacers are a stock item at the LBS? We’re going on a ride tomorrow afternoon, so hope so!
Thanks everyone for your help, I’ve learnt a lot tonight.Posted 4 years ago
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