Rear mech wont go to smallest cog

JimboPlob

I have recently cabled up a new frame. Its a brand new mech hanger, cables etc...

I have adjusted the limiter screws as much as I can, but the mech just wont let the chain go into the smallest cog.

Its a Dura Ace 7800 rear mech and am running a 9 speed chain and cassette.

Any ideas?

napoleond

Yes, you are using a 10 speed rear mech

mcp73

I was under the impression that rear mechs are 'dumb', i.e. they move as determined by the cable pull from the shifter. Is this not the case?

zx6man

Sorry to ask, the shifters are 9 speed?

nicklouse

JimboPlob wrote:

I have recently cabled up a new frame. Its a brand new mech hanger, cables etc...

I have adjusted the limiter screws as much as I can, but the mech just wont let the chain go into the smallest cog.

Its a Dura Ace 7800 rear mech and am running a 9 speed chain and cassette.

Any ideas?

bent mech hanger/frame?
mech fitted correctly?
too much tension in the cable?
take chain off and disconect the cable and check that the mech moves cleanly with no obstruction.

JimboPlob

10 speed rear mech, 9 speed shifters.. But, shifting to all other gears works flawlesly.

Taking all tension out of cable doesnt work. Its a brand new mech hanger.

smidsy

So 9 speed STI's, 9 speed cassette, 9 speed chain.

Yes the rear mech is 'dumb' and the cable pull is indeed the thing that determines the amount of 'jump' between cogs.

I take it that you have a spare click left in the STI when you get to the penultimate gear (i.e the STI has another gear left in it).

If so then the rear mech limit has to be the answer.

If not adjust the barrell adjuster so it forces the chain onto the last cog which will then put the STI and chain position in sink with one another. You should then be able to select all the cassette.

nicklouse

JimboPlob wrote:

Its a brand new mech hanger.

means little.
again disconnect every thing and see what it does.

as it will highlight what you have done wrong if anything.

Monty Dog

Disconnect gear cable from mech and see if it runs in the small sprocket - adjust stop screw if needed. Visually check to see if the jockey wheel cage is vertically aligned. No problem using a 10 speed Shimano mech with 9 speed road shifter /drivetrain as cable-pull ratio is the same.

JimboPlob

When everything is disconnected, the limit screw will not allow the rear mech to put the chain into the smallest cog. Its like the limit screw doesn't allow it to go far enough out. Yes, I am sure I am turning the correct limit screw. if I tighten it, the rear mech visibly moves inwards.

I can visually see the jockey wheel will not physically move out far enough to ever get the chain onto the smallest cog.

nicklouse

JimboPlob wrote:

When everything is disconnected, the limit screw will not allow the rear mech to put the chain into the smallest cog. Its like the limit screw doesn't allow it to go far enough out. Yes, I am sure I am turning the correct limit screw. if I tighten it, the rear mech visibly moves inwards.

I can visually see the jockey wheel will not physically move out far enough to ever get the chain onto the smallest cog.

then bent frame/mech hanger or mech.

JimboPlob

I suspect its the mech. Is there any way to bend the mech back?

zx6man

Is the framestays at the back a different width, needing spaces on the axle to make the cassette sit in the correct place?

Monty Dog

Doubt it's anything to do with drop-out width/spacing - the rear mech cage should be able to move outboard of the frame if correctly aligned. Sounds like the gear hanger is bent - ask your LBS to check rear hanger alignment, it's a simple job