Rear Mech Trouble

dave82uk

I have been having trouble setting up my rear mech. Recently its started skipping gears whenever I'm in a low gear. Spent this afternoon trying to re-set them but it seems as if the mechs moving too much each time i click the shifter e.g. If I adust it so that the pulley is lined up with the highest gear when i shift down into 2nd lowest gear the pulley is almost inline with the lowest gear.

I've tried two different mechs, checked cables, hanger doesn't seem bent, cables are clamped to mech correctly, shifter seems fine.

Is there anything else I'm missing?

nicklouse

what is the shifter?
what is the mech?

is the mech hanger bent?

dave82uk

Deore shifter, LX rear mech. Hanger seems fine.

nicklouse

nothing else changed?

dirty cables or too much tension in the cable.

MrChuck

Have you threaded the chain through the jockey wheels and cage properly- and round that little tab?

Of course you'd need to be pretty dopey to do that... ahem :roll:

dave82uk

Nothing else has changed, I've cleaned and lubed all the cables and tension seems fine. Only thing that has happened recently is I had the chain break a few weeks ago but I have had it shifting fine since then.

supersonic

So if you back the tesnion of slighlty it does not improve, ie an eighth of a turn at a time?

If you release all cable tension, does the mech fall back to the H stop, which should be lined up with the smallest cog.

dave82uk

No improvement if I back of the tension. I've got H and L stops adjusted. If I add just enough tension to get It to change down through the gears It then takes 2 clicks to get it to change from the largest to second largest cog.

AndyI

Have your frame checked. An LBS owner/mechanic with years of experience told me about a similar problem, couldn't find the fault, eventually discovered that the frame had a micro crack on one of the welds and when riding pressure was applied it was enough to distort the frame sufficiently to release tension on the mech cable, resulting in ghost shifting. The micro crack was only visible when pressure was applied across the joint. I hope this isn't your problem as it would be expensive to fix, and it may be a long shot, but it's worth checking. if all obvious checks have failed

supersonic

Really does sound like a cable problem, classic symptoms. I'd check each outer section, ensuring the cable glides smoothly through each piece, and there are no burrs.

dave82uk

I'll check my cables again but i'm sure there fine. Is there anything I'm missing that could cause it to index too much? If I back off the h and l limits and adjust the tension so that the puley is lined up with the small cog by the time I shift down into lowest gear I can see the puley is well past the largest cog.

supersonic

The above method would be using too much tension - using excess cable tension to align the H gear rather than its stop.

Try backing off the tension again and adjusting the H stop inwards until you hear it rattling on the next cog. Back it off until it stops.

Now try indexing.

nicklouse

as sonic says set the stops first then the tension for the shifts.

dave82uk

The problem is if I add enough tension to shift through the smaller gears when I get to the larger gears Its as if I have too much tension and vice versa.

supersonic

WHich points back to the spring tension not pushing the cable back through effectively.

Gonna be hard to say really without coming and having a look! Maybe needs another set of eyes?

nicklouse

thank god i am building two single speeds tomorrow.

supersonic

Pervert ;-)

dave82uk

Yeah, think I'll admit defeat on this one and get lbs to have a look. Cheers for help anyway.

supersonic

One of those things I'm afraid, sorry we couldn't be of more help.

konanige

Hi dont know if this will be of any help but I had a similar problem with my PlanetX Armadillo and it turned out that although the gear indexing seemed to be fine the gears wouldnt change correctly whatever I did. Of course when you find out that the rear mechs job is just to suggest to the chain that it should move in a certain direction and all the ramps and pins and machining on the chain actually do the shifting I found the solution to my problem, so with new chain and rear cluster installed hey presto luverly gear changes! Hope this is of help to you ,Good luck.